Posterior fossa volume and response to suboccipital decompression in patients with Chiari I malformation

Base of Skull & Spinal Canal Narrowing in an Adolescent with Autosomal Recessive Hypophosphatemic Rickets Type 2

Autosomal recessive hypophosphatemic rickets type 2 (ARHR2) is an uncommon hereditary form of rickets characterised by chronic renal phosphate loss and impaired bone mineralisation. This results from compound heterozygous or homozygous pathogenic variants in ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1), a key producer of extracellular inorganic pyrophosphate (PPi) and an inhibitor of fibroblast growth factor23 (FGF23). ENPP1 deficiency impacts FGF23 and increases its activity. Inactivating ENPP1 variants are associated with both Generalised Arterial Calcification of Infancy (GACI) and ARHR2, even within the same family. Both conditions share a deficiency of ENPP1, displaying clinical variability without a clear genotype-phenotype correlation. Whilst pathogenic ENPP1 variants are known to be associated with various phenotypes, including vascular calcification, hearing loss, ossification of the posterior longitudinal ligament (OPLL), and pseudoxanthoma elasticum (PXE), skull changes have not been reported to our knowledge. We present herein a case of a 10-year-old girl with ARHR2, due to compound heterozygous pathogenic ENPP1 variants, who was found to have papilledema on a routine eye test. Neuroimaging revealed enlarged lateral ventricles, compression of the spinal cord at the foramen magnum with Chiari 1 malformation and a retroverted odontoid peg. She underwent two endoscopic third ventriculostomy procedures to manage the hydrocephalus and a further foramen magnum decompression procedure to alleviate her headaches and neck pain concerns. Individuals with ARHR2 may experience alterations at the base of the skull, potentially leading to base of skull narrowing, chronic hydrocephalus, and Chiari malformation.

Perioperative Segmentation of the Posterior Fossa and the Keel of Goodrich in Surgical Outcomes of Chiari Malformations

BACKGROUND

Chiari I malformation (CM-I) is defined as the extension of brain tissue into the spinal cord. This study aimed to refine the methodology for the acquisition of 3-dimensional measurements of the posterior fossa and introduce occipital keel size as a new marker and its impact in patients with CM.

METHODS

In this retrospective study, all patients who underwent Chiari decompression surgery at Montefiore Medical Center from April 2012 to April 2022 were included. Perioperative clinical information was obtained in addition to maximal keel thickness (KT), foramen magnum area, and preoperative and postoperative posterior fossa volumes for each patient and age-matched controls. Volumetric measurements were obtained using artificial intelligence-based semiautomated segmentation.

RESULTS

A total of 107 patients with CM including 37 males, and 70 females were studied with a mean age of 26.56 ± 17.31 compared with 103 controls without CM. The comparison between the CM and the general population groups demonstrated a significantly increased keel size in Chiari patients. Keel size had a significant relationship with dysphagia, paresthesia, and intraoperative blood loss, while posterior volume change had a significant relationship with sex and early symptomatic improvement. The Foramen magnum area was related to tonsillar descent and more prominent in patients with spina bifida.

CONCLUSIONS

The Keel of Goodrich is a new anatomical factor that should be taken into consideration when evaluating preoperative symptoms, and intraoperative complications in patients with CM-I. Volumetric analyses demonstrated that posterior fossa volume change had a significant impact on early symptom improvement in patients with Chiari, as did the choice of operative approach. The routine use of semiautomated segmentation of the posterior fossa may help stratify Chiari patients in the future and should be implemented in routine clinical care.

Multi-Dimensional Morphometric and Volumetric Analysis of the Posterior Cranial Fossa to Study Type I Chiari Malformation

BACKGROUND

Chiari malformation type I (CM-1) is a complex disorder in which tonsillar herniation through the foramen magnum (FM) manifests with a spectrum of clinical symptoms. This work analyzes morphometric and volumetric characteristics of CM-1 patients.

METHODS

With institutional review board approval, we retrospectively reviewed a total of 72 adult CM-1 patients and 26 healthy adult volunteers who underwent volumetric magnetic resonance brain imaging. Clinical data were retrospectively extracted from the electronic medical record. We analyzed multidimensional morphometric and volumetric features within the posterior cranial fossa and correlated these features with syrinx formation and the decision to undergo surgical decompression.

RESULTS

In our study, CM-1 patients had decreased cerebellar (CBL), brainstem, and fourth ventricular volumes but larger tonsillar volume with increased total tonsillar length. CM-1 patients who underwent surgery had significantly more neural tissue within the cross-sectional area of the cisterna magna. Logistic regression demonstrated that combining neural tissue at the FM with CBL and fourth ventricular volumes led to a great degree of correlation with syrinx formation (area under the curve: 0.911).

CONCLUSIONS

Our findings suggest that the amount of tissue at the FM correlates with CM-1 patients who underwent decompressive surgery, more so than tonsillar length. Additionally, the combination of neural tissue at the FM, CBL, and fourth ventricular volumes led to a great degree of correlation with syrinx formation. Together, these findings suggest that a global compressive phenomenon within the posterior fossa leads to CM-1 symptomatology and syrinx formation.

Infant Hydrocephalus

Hydrocephalus is a neurosurgical condition that is highly prevalent in pediatric medicine. In the infant population, there is a distinct set of features that all primary pediatricians would benefit from understanding. Infant hydrocephalus can present prenatally on imaging and postnatally with symptomatic enlargement of the head and associated skull features and raised intracranial pressures. The 2 major pathophysiology models of infant hydrocephalus are the bulk flow and the intracranial pulsatility models. The most common acquired forms of hydrocephalus include posthemorrhagic hydrocephalus, postinfectious hydrocephalus, and brain tumor. The most common congenital forms of hydrocephalus include those due to myelomeningocele, aqueductal stenosis, and posterior fossa malformations. There are various evaluation and treatment algorithms for these different types of hydrocephalus, including cerebrospinal fluid shunting and endoscopic third ventriculostomy. The aim of this review was to elaborate on those features of hydrocephalus to best equip primary pediatricians to diagnose and manage hydrocephalus in infants.

Volumetric assessment of Posterior cranial fossa in a West African population

BACKGROUND AND OBJECTIVES

Posterior fossa pathologies can have potentially devastating outcomes. The volumetric capacity of this fossa, known to have ethnoregional variations, can thus be critical in determining outcomes and intervention measures and approaches to pathologies involving this region. This study aimed to evaluate the normal posterior fossa volumes within the West-African subpopulation.

METHODS

This was a descriptive study of all patients presenting for a cranial imaging study at the study location within a two-year period using a 1.5T MRI of this cranial region. Obtained data included the transverse and anteroposterior diameters, and the height of this fossa and the obtained data was analyzed. P values < 0.05 was statistically significant.

RESULTS

A total of 315 patients were recruited (165 males and 150 females). The average posterior fossa transverse diameter, anteroposterior diameter and height were 108.19 mm, 71.58 mm and 35.53 mm respectively for males, and 105.7 mm, 66.48 mm, and 34.24 mm for females respectively. The average posterior fossa volume for males (292.36 cm3) was significantly higher than for females (252.90 cm3) (p= 0.0038). The highest average posterior fossa volume was between 16-30 years for males and above 75 years for females.

CONCLUSION

Posterior cranial fossa volumes for the West African population is significantly higher than those obtained for other regions. In addition to being beneficial in some posterior fossa space occupying lesions, this larger volume can explain the relative rarity and sexual preferences of some posterior fossa congenital abnormalities like Chiari-1 malformation amongst the West African population.

Enhancing Hierarchical Transformers for Whole Brain Segmentation with Intracranial Measurements Integration

Whole brain segmentation with magnetic resonance imaging (MRI) enables the non-invasive measurement of brain regions, including total intracranial volume (TICV) and posterior fossa volume (PFV). Enhancing the existing whole brain segmentation methodology to incorporate intracranial measurements offers a heightened level of comprehensiveness in the analysis of brain structures. Despite its potential, the task of generalizing deep learning techniques for intracranial measurements faces data availability constraints due to limited manually annotated atlases encompassing whole brain and TICV/PFV labels. In this paper, we enhancing the hierarchical transformer UNesT for whole brain segmentation to achieve segmenting whole brain with 133 classes and TICV/PFV simultaneously. To address the problem of data scarcity, the model is first pretrained on 4859 T1-weighted (T1w) 3D volumes sourced from 8 different sites. These volumes are processed through a multi-atlas segmentation pipeline for label generation, while TICV/PFV labels are unavailable. Subsequently, the model is finetuned with 45 T1w 3D volumes from Open Access Series Imaging Studies (OASIS) where both 133 whole brain classes and TICV/PFV labels are available. We evaluate our method with Dice similarity coefficients(DSC). We show that our model is able to conduct precise TICV/PFV estimation while maintaining the 132 brain regions performance at a comparable level. Code and trained model are available at: https://github.com/MASILab/UNesT/wholebrainSeg.

A morphometric study of the atlanto-occipital joint in adult patients with Chiari malformation type I

BACKGROUND

There are many morphometric studies on Chiari malformation type I (CMI) patients, most of which focus on the posterior cranial fossa (PCF). Less attention has been paid to the atlanto-occipital joint. In this study, we aim to evaluate the morphological characteristics of the atlanto-occipital joint in CMI patients.

MATERIALS AND METHODS

The cervical CT imaging data of adult patients diagnosed with CMI but without any bony malformation in craniovertebral junction (CVJ) who were treated by the authors between January 2014 and December 2019 were retrospectively analyzed. The equal number of sex and age-matched healthy individuals were included as the control group. The morphometric analysis was performed by measuring the length and depth of the atlanto-occipital joint, and the depth/length ratio was calculated to evaluate the curvature of the joint.

RESULTS

A total of 47 patients (15 males and 32 females) were included. The mean age of patients was 47.49 ± 9.01 years (range 19-62 years). The mean depth/length ratio of the atlanto-occipital joint in CMI patients was 0.141 ± 0.065 (range 0.027 - 0.274), which was smaller than that of control individuals (0.228 ± 0.057, range 0.069 - 0.379). And the difference was statistically significant (p < .01).

CONCLUSIONS

The atlanto-occipital joints in CMI patients are significantly flatter compared with those in healthy controls. This morphological variation could lead to differences of the atlanto-occipital stability between CMI patients and normal population, which may be related to the pathogenesis of CMI.

Morphological and ultrastructural investigation of the posterior atlanto-occipital membrane: Comparing children with Chiari malformation type I and controls

INTRODUCTION

The fibrous posterior atlanto-occipital membrane (PAOM) at the craniocervical junction is typically removed during decompression surgery for Chiari malformation type I (CM-I); however, its importance and ultrastructural architecture have not been investigated in children. We hypothesized that there are structural differences in the PAOM of patients with CM-I and those without.

METHODS

In this prospective study, blinded pathological analysis was performed on PAOM specimens from children who had surgery for CM-I and children who had surgery for posterior fossa tumors (controls). Clinical and radiographic data were collected. Statistical analysis included comparisons between the CM-I and control cohorts and correlations with imaging measures.

RESULTS

A total of 35 children (mean age at surgery 10.7 years; 94.3% white) with viable specimens for evaluation were enrolled: 24 with CM-I and 11 controls. There were no statistical demographic differences between the two cohorts. Four children had a family history of CM-I and five had a syndromic condition. The cohorts had similar measurements of tonsillar descent, syringomyelia, basion to C2, and condylar-to-C2 vertical axis (all p>0.05). The clival-axial angle was lower in patients with CM-I (138.1 vs. 149.3 degrees, p = 0.016). Morphologically, the PAOM demonstrated statistically higher proportions of disorganized architecture in patients with CM-I (75.0% vs. 36.4%, p = 0.012). There were no differences in PAOM fat, elastin, or collagen percentages overall and no differences in imaging or ultrastructural findings between male and female patients. Posterior fossa volume was lower in children with CM-I (163,234 mm3 vs. 218,305 mm3, p<0.001), a difference that persisted after normalizing for patient height (129.9 vs. 160.9, p = 0.028).

CONCLUSIONS

In patients with CM-I, the PAOM demonstrates disorganized architecture compared with that of control patients. This likely represents an anatomic adaptation in the presence of CM-I rather than a pathologic contribution.

Evaluation and Treatment of Patients with Small Posterior Cranial Fossa and Chiari Malformation, Types 0 and 1

The diagnosis of Chiari I malformation is straightforward in patients with typical signs and symptoms of Chiari I malformation and magnetic resonance imaging (MRI) confirming ≥5 mm of cerebellar tonsillar ectopia, with or without a syrinx. However, in many cases, Chiari I malformation is discovered incidentally on MRI to evaluate global headache, cervical radiculopathy, or other conditions. In those cases, the clinician must consider if cerebellar tonsillar ectopia is related to the presenting symptoms. Surgical decompression of the cerebellar tonsils and foramen magnum in patients with symptomatic Chiari I malformation effectively relieves suboccipital headache, reduces syrinx distension, and arrests syringomyelia progression. Neurosurgeons must avoid operative treatments decompressing incidental tonsillar ectopia, not causing symptoms. Such procedures unnecessarily place patients at risk of operative complications and tissue injuries related to surgical exploration. This chapter reviews the typical signs and symptoms of Chiari I malformation and its variant, Chiari 0 malformation, which has <5 mm of cerebellar tonsillar ectopia and is often associated with syringomyelia. Chiari I and Chiari 0 malformations are associated with incomplete occipital bone development, reduced volume and height of the posterior fossa, tonsillar ectopia, and compression of the neural elements and cerebrospinal fluid (CSF) pathways at the foramen magnum. Linear, angular, cross-sectional area, and volume measurements of the posterior fossa, craniocervical junction, and upper cervical spine identify morphometric abnormalities in Chiari I and Chiari 0 malformation patients. Chiari 0 patients respond like Chiari I patients to foramen magnum decompression and should not be excluded from surgical treatment because their tonsillar ectopia is <5 mm. The authors recommend the adoption of diagnostic criteria for Chiari 0 malformation without syringomyelia. This chapter provides updated information and guidance to the physicians managing Chiari I and Chiari 0 malformation patients and neuroscientists interested in Chiari malformations.

Growth patterns and ratios of posterior cranial fossa structures in the Japanese pediatric population: a study utilizing CT scans

PURPOSE

The changes in the proportion of posterior cranial fossa structures during pediatric development remain unclear. This retrospective study aimed to investigate the growth patterns and ratios of these structures using CT scans.

METHODS

Head CT scans of pediatric patients with minor head trauma from Osaka Women's and Children's Hospital between March 2006 and May 2023 were analyzed. The study segmented the intracranial volume (ICV), posterior cranial fossa volume (PCFV), cerebellum volume (CBMV), and brainstem volume (BSV). Correlation coefficients were calculated among the parameters. Patients aged 0 to 10 years were divided into 15 age-related clusters, and mean and standard deviation values were measured. Growth curves were created by plotting mean values sequentially. Ratios such as PCFV/ICV and (CBMV + BSV)/PCFV were examined. Statistical analyses, including unpaired t tests and logarithmic curve fitting, were performed.

RESULTS

A total of 234 CT scans (97 from females, 115 from infants under 1 year of age) were analyzed. Positive correlations were observed among the parameters, with the strongest between PCFV and CBMV. The growth curves for ICV, PCFV, CBMV, and BSV exhibited a two-phase process, with rapid growth until approximately 4 years of age, followed by stabilization. The ratios PCFV/ICV and (CBMV + BSV)/PCFV showed increasing trends from birth onwards, stabilizing by 4 and 1 years of age, respectively.

CONCLUSION

This study provides insights into the growth patterns and ratios of posterior cranial fossa structures in the pediatric population. The findings demonstrate a two-phase growth process and increasing trends in the examined ratios.

Decoding Chiari Malformation and Syringomyelia: From Epidemiology and Genetics to Advanced Diagnosis and Management Strategies

Chiari Malformation and Syringomyelia are neurosurgical entities that have been the subject of extensive research and clinical interest. Globally prevalent, these disorders vary demographically and have witnessed evolving temporal trends. Chiari Malformation impacts the normal cerebrospinal fluid flow, consequently affecting overall health. Key observations from canine studies offer pivotal insights into the pathogenesis of Syringomyelia and its extrapolation to human manifestations. Genetics plays a pivotal role; contemporary knowledge identifies specific genes, illuminating avenues for future exploration. Clinically, these disorders present distinct phenotypes. Diagnostically, while traditional methods have stood the test of time, innovative neurophysiological techniques are revolutionizing early detection and management. Neuroradiology, a cornerstone in diagnosis, follows defined criteria. Advanced imaging techniques are amplifying diagnostic precision. In therapeutic realms, surgery remains primary. For Chiari 1 Malformation, surgical outcomes vary based on the presence of Syringomyelia. Isolated Syringomyelia demands a unique surgical approach, the effectiveness of which is continually being optimized. Post-operative long-term prognosis and quality of life measures are crucial in assessing intervention success. In conclusion, this review amalgamates existing knowledge, paving the way for future research and enhanced clinical strategies in the management of Chiari Malformation and Syringomyelia.

Intraoperative occipital to C2 angle and external acoustic meatus-to-axis angular measurements for optimizing alignment during posterior fossa decompression and occipitocervical fusion for complex Chiari malformation

Background

Excess flexion or extension during occipitocervical fusion (OCF) can lead to postoperative complications, such as dysphagia, respiratory problems, line of sight issues, and neck pain, but posterior fossa decompression (PFD) and OCF require different positions that require intraoperative manipulation.

Objective

The objective of this study was to describe quantitative fluoroscopic morphometrics in Chiari malformation (CM) patients with symptoms of craniocervical instability (CCI) and demonstrate the intraoperative application of these measurements to achieve neutral craniocervical alignment while leveraging a single axis of motion with the Mayfield head clamp locking mechanism.

Methods

A retrospective cohort study of patients with CM 1 and 1.5 and features of CCI who underwent PFD and OCF at a single-center institution from March 2015 to October 2020 was performed. Patient demographics, preoperative presentation, radiographic morphometrics, operative details, complications, and clinical outcomes were analyzed.

Results

A total of 39 patients met the inclusion criteria, of which 37 patients (94.9%) did not require additional revision surgery after PFD and OCF. In this nonrevision cohort, preoperative to postoperative occipital to C2 angle (O-C2a) (13.5° ± 10.4° vs. 17.5° ± 10.1°, P = 0.047) and narrowest oropharyngeal airway space (nPAS) (10.9 ± 3.4 mm vs. 13.1 ± 4.8 mm, P = 0.007) increased significantly. These measurements were decreased in the two patients who required revision surgery due to postoperative dysphagia (mean difference - 16.6°° in O C2a and 12.8°° in occipital and external acoustic meatus to axis angle). Based on these results, these fluoroscopic morphometrics are intraoperatively assessed, utilizing a locking Mayfield head clamp repositioning maneuver to optimize craniocervical alignment prior to rod placement from the occipital plate to cervical screws.

Conclusion

Establishing a preoperative baseline of reliable fluoroscopic morphometrics can guide surgeons intraoperatively in appropriate patient realignment during combined PFD and OCF, and may prevent postoperative complications.

Combined Cerebrospinal Fluid Hydrodynamics and Fourth Ventricle Outlet Morphology to Improve Predictive Efficiency of Prognosis for Chiari Malformation Type I Decompression

OBJECTIVE

To identify the morphological characteristics together with cerebrospinal fluid (CSF) hydrodynamics on preoperative magnetic resonance imaging that improve the prediction of foramen magnum decompression (FMD) treatment outcome for Chiari malformations type I (CM-I) patients compared with the CSF hydrodynamics-based model.

METHODS

This retrospective study included CM-I patients who underwent FMD, phase-contrast cine magnetic resonance, and static MR between January 2018 and March 2022. The relationships of the preoperative CSF hydrodynamic quantifications derived from phase-contrast cine magnetic resonance and morphological measurements from static magnetic resonance imaging, clinical indicators with different outcomes, were analyzed with logistic regression analysis. The outcomes were determined using the Chicago Chiari Outcome Scale. The predictive performance was evaluated with receiver operating characteristic, calibration, decision curves and area under the receiver operating characteristic curve, net reclassification index, and integrated discrimination improvement and was compared with CSF hydrodynamics-based model.

RESULTS

A total of 27 patients were included. 17 (63%) had improved outcomes and 10 (37%) had poor outcomes. The peak diastolic velocity of the aqueduct midportion (odd ratio, 5.17; 95% confidence interval: 1.08, 24.70; P = 0.039) and the fourth ventricle outlet diameter (odd ratio, 7.17; 95% confidence interval: 1.07, 48.16; P = 0.043) were predictors of different prognoses. The predictive performance improved significantly than the CSF hydrodynamics-based model.

CONCLUSIONS

Combined CSF hydrodynamic and static morphologic MR measurements can better predict the response to FMD. A higher peak diastolic velocity of the aqueduct midportion and broader fourth ventricle outlet were associated with satisfying outcomes after decompression in CM-I patients.

The Chiari Malformations: A Bibliometric Analysis of the 100 Most Cited Articles

OBJECTIVE

The Chiari malformations present heterogeneous entities, raising many questions regarding their natural history, pathophysiology, treatment options, and prognosis. Bibliometric analyses have emerged as a method to assess the impact of articles in current clinical practice.

METHODS

The most cited articles were identified via Scopus Library by using the keywords "Chiari," "Arnold-Chiari," and "Chiari malformation." The 100 most cited articles were then assembled and analyzed in detail.

RESULTS

The top 100 articles yielded a mean of 155,28 citations per article, ranging from 87 to 896 citations, and from 1.63 to 38.96 per year. Years of publications ranged from 1950 to 2015. Oakes was the most cited author (n = 7), followed by Tubbs and Milhorat. The country with the highest cited articles was the United States (n = 63), followed by the United Kingdom (n = 6), Italy (n = 5), Spain (n = 5), Japan (n = 4), and Germany (n = 3). Neurosurgery is the journal with the most highly cited articles (n = 21), followed by Journal of Neurosurgery (n = 19). Most articles focused on Chiari malformation type I (n = 83). The topic discussed most often was imaging (n = 63), followed by the evaluation of treatment outcome (n = 58), clinical signs and symptoms (n = 57), and the role of surgery (n = 56).

CONCLUSIONS

The present bibliometric analysis provides a succinct appraisal of the most cited articles concerning Chiari malformation, allowing a deeper insight in this area and its main influential articles with their impact on current clinical practice and future research.

C1-2 Fusion in Atlantoaxial Dislocation and Basilar Invagination with and without Chiari Malformation: Clinical/Radiological and Craniometric Results

OBJECTIVE

Patients with Chiari malformation (CM) associated with atlantoaxial dislocation (AAD) and basilar invagination (BI) may present with a small posterior cranial fossa, but data on the volumetric analysis are lacking. Additionally, whether additional foramen magnum decompression (FMD) is needed together with atlantoaxial fusion remains controversial. This study evaluated the volumetric alterations of the posterior cranial fossa in these patients and analyzed the radiological and clinical outcomes after posterior C1-C2 reduction and fixation plus C1 posterior arch resection.

METHODS

Thirty-two adult CM patients with AAD and BI (CM-AAD/BI group) and 21 AAD and BI patients without CM (AAD/BI-only group) who received posterior atlantoaxial fusion plus C1 posterior arch resection were retrospectively studied. The clinical and radiological outcomes and volumetric measurements of the posterior cranial fossa were evaluated.

RESULTS

The majority of CM-AAD/BI patients (94%) improved clinically and radiologically at 12 mo postoperatively, and none required additional FMD. Morphological analysis revealed a significant reduction in the bony posterior cranial fossa volumes of the CM-AAD/BI group (P < 0.01) and the AAD/BI-only group (P < 0.01) relative to those of the CM group. No significant differences were observed between the CM-AAD/BI and AAD/BI groups.

CONCLUSIONS

Compared with patients with simple CM, patients with AAD/BI with or without CM demonstrated a considerably and equally reduced bony posterior cranial fossa volume. No additional FMD is needed in the treatment of CM-AAD/BI patients after posterior reduction and fusion plus C1 posterior arch resection.

Minimally invasive foramen magnum decompression using tubular retractors (MIFT) for Chiari I malformations

BACKGROUND

Chiari malformation type 1 has been traditionally treated with foramen magnum decompression and C1 arch excision with or without duroplasty depending on the surgeon's preference. Each of the various surgical modifications has its advantages and disadvantages.

METHODS

We describe a minimally invasive tubular retractor-based approach to achieve bony decompression in these cases. We have had good results comparable to the open approach.

CONCLUSIONS

Strict orientation to the midline using soft tissue landmarks in between the muscles and bony landmarks in the deeper planes is important to achieve good surgical results. Operative time decreases with expertise and is comparable to the open technique. Minimal blood loss and decreased hospital stay and an excellent cosmetic scar make this procedure more appealing.

A new supportive approach in the diagnosis of Chiari malformation type 1 in pediatric patients

PURPOSE

Chiari malformation type 1 (CM-1) is a posterior fossa anomaly characterized by herniation of the cerebellar tonsils from the foramen magnum (FM). This study compares FM, medulla spinalis (MS), and herniated cerebellar tonsils ratios by making area measurements from axial plane MRI in CM-1 patients and the control group.

METHODS

Our study evaluated 30 pediatric patients with CM-1 and 30 people in the control group. The lengths of the McRae line, twining line, and clivus line were measured on the posterior cranial fossa evaluation. The areas of FM (A_FM), MS (A_MS), and herniated cerebellar tonsils (A_TONSILS) were measured by axial images.

RESULTS

As a result of area measurements obtained from axial cross-sectional MRI, a statistically significant difference was found between CM-1 patients and the control group. According to the results of the ROC analysis, if an individual's A_MS/A_FM value is above 17.9% or the A_TONSILS/A_FM value is above 18.4%, it can be interpreted as a CM-1 patient.

CONCLUSION

It will be easier to diagnose the patient with the new approach we obtained from axial MR images in addition to sagittal MR images. This method can be a guide in some cases when the surgeons are undecided.

The Small Posterior Cranial Fossa Syndrome and Chiari Malformation Type 0

Patients showing typical Chiari malformation type 1 (CM1) signs and symptoms frequently undergo cranial and cervical MRI. In some patients, MRI documents >5 mm of cerebellar tonsillar herniation (TH) and the diagnosis of CM1. Patients with 3−5 mm TH have “borderline” CM1. Patients with less than 3 mm of TH and an associated cervical syrinx are diagnosed with Chiari “zero” malformation (CM0). However, patients reporting CM1 symptoms are usually not diagnosed with CM if MRI shows less than 3−5 mm of TH and no syrinx. Recent MRI morphometric analysis of the posterior fossa and upper cervical spine detected anatomical abnormalities in and around the foramen magnum (FM) that explain these patients’ symptoms. The abnormalities include a reduced size of the posterior fossa, FM, and upper cervical spinal canal and extension of the cerebellar tonsils around the medulla rather than inferior to the foramen magnum, as in CM1. These morphometric findings lead some neurologists and neurosurgeons to diagnose CM0 in patients with typical CM1 signs and symptoms, with or without cervical syringes. This article reviews recent findings and controversies about CM0 diagnosis and updates current thinking about the clinical and radiological relationship between CM0, borderline CM1, and CM1.

Surgical Management of Chiari Malformation Type I Associated with Syringomyelia: Outcome of Surgeries Based on the New Classification and Study of Cerebrospinal Fluid Dynamics

Introduction: The mainstay of treatment of syringomyelia associated with Chiari malformation type I (CM-I) is the management of CM-I to normalize the cerebrospinal fluid (CSF) flow at the foramen magnum. CM-I is classified into three independent types. Surgical treatment was selected based on the mechanism of hindbrain ptosis in each CM-I type. Materials and Methods: Foramen magnum decompression (FMD: 213 cases), expansive suboccipital cranioplasty (ESCP: 87 cases), and craniocervical fixation (CCF: 30 cases) were performed. CSF flow dynamics were assessed pre- and post-surgery using cine phase contrast magnetic resonance imaging. During surgery, CSF flow dynamics were examined using color Doppler ultrasonography (CDU). Results: ESCP and FMD demonstrated high rates of improvement in neurological symptoms and signs (82.7%), whereas CCF demonstrated a high rate of improvement in neurological symptoms (89%). The pre-operative maximum flow velocity (cm/s) was significantly lower in patients than in controls and increased post-operatively. During surgery, CDU indicated that the volume of the major cistern was 8 mL, and the maximum flow velocity was >3 mL/s. Conclusions: An appropriate surgical treatment should be selected for CM-I to correct hindbrain ptosis. In addition, it is necessary to confirm the normalization of CSF flow at the foramen of Magendie.

Generalizing deep learning brain segmentation for skull removal and intracranial measurements

Total intracranial volume (TICV) and posterior fossa volume (PFV) are essential covariates for brain volumetric analyses with structural magnetic resonance imaging (MRI). Detailed whole brain segmentation provides a non-invasive way to measure brain regions. Furthermore, increasing neuroimaging data are distributed in a skull-stripped manner for privacy protection. Therefore, generalizing deep learning brain segmentation for skull removal and intracranial measurements is an appealing task. However, data availability is challenging due to a limited set of manually traced atlases with whole brain and TICV/PFV labels. In this paper, we employ U-Net tiles to achieve automatic TICV estimation and whole brain segmentation simultaneously on brains w/and w/o the skull. To overcome the scarcity of manually traced whole brain volumes, a transfer learning method is introduced to estimate additional TICV and PFV labels during whole brain segmentation in T1-weighted MRI. Specifically, U-Net tiles are first pre-trained using large-scale BrainCOLOR atlases without TICV and PFV labels, which are created by multi-atlas segmentation. Then the pre-trained models are refined by training the additional TICV and PFV labels using limited BrainCOLOR atlases. We also extend our method to handle skull-stripped brain MR images. From the results, our method provides promising whole brain segmentation and volume estimation results for both brains w/and w/o skull in terms of mean Dice similarity coefficients and mean surface distance and absolute volume similarity. This method has been made available in open source (https://github.com/MASILab/SLANTbrainSeg_skullstripped).

Assessment of patients with a Chiari malformation type I

Introduction

The prevalence of Chiari malformation type I (CM-I) has been estimated as up to 1% of the general population. The majority of patients are asymptomatic and usually do not need treatment. Symptomatic patients, and some asymptomatic patients with associated conditions, may benefit from further assessment and treatment.

Research question

The aim of this review was to describe the clinical and radiological assessment of patients presenting with a CM-I.

Material and methods

A literature search was performed using the PubMed and Embase databases focused on clinical assessment and imaging techniques used to diagnose CM-I.

Results

Following a complete clinical evaluation in patients with symptomatic CM-I and/or radiologically significant CM-I (tonsillar impaction, resulting tonsillar asymmetry and loss of CSF spaces), MRI of the brain and whole spine enables an assessment of the CM-I and potential associated or causative conditions. These include hydrocephalus, syringomyelia, spinal dysraphism, and tethered cord. Flow and Cine MRI can provide information on CSF dynamics at the craniocervical junction, and help in surgical decision-making. Hypermobility or instability at the upper cervical and craniocervical junction is less common and can be measured with CT imaging and flexion/extension or upright MRI.

Discussion and conclusion

The majority of CM-I detected are incidental findings on MRI imaging of brain or spine, and do not require intervention. Once a radiological diagnosis and concern has been raised, clinical assessment by an appropriate specialist is required. A MRI brain and cervical spine is indicated in all radiologically labelled CM-I. In symptomatic patients or cases of radiologically significant CM-I, MRI of the brain and entire spine is indicated. Further investigations should be tailored to individuals' needs.

CSF-space volumetric change following posterior fossa decompression in paediatric Chiari type-I malformation: a correlation with outcome

OBJECTIVE

We have previously reported inferior post-operative clinical outcomes in younger children with Chiari type-I malformation (CIM). We sought to quantify the CSF volumetric changes pre- and post-decompression, in a paediatric cohort, to determine whether cisternal volume change is associated with clinical outcomes.

METHODS

In this retrospective clinical study, the CSF spaces of the posterior fossa (supracerebellar/quadrigeminal, prepontine, fourth ventricle, cisterna magna) were measured on magnetic resonance images pre- and post-operatively using a semi-automated method. Additionally, we describe a novel CSF space of the upper cervical canal incorporating the subarachnoid space from the foramen magnum to the inferior cortex of the C2 body, FM-C2 cistern. Morphometric measurements included the pB-C2 distance, clivoaxial angle, clival length, clival angle and Boogard's angle. Volumetric and morphometric data were correlated with clinical outcomes at 4-12 months post-operatively as measured by the Chicago Chiari Outcome Scale (CCOS).

RESULTS

Of 59 adequate clinical cases, 57 and 36 patients had acceptable imaging for morphometric and volumetric analysis respectively. All CSF spaces measured had a significant increase in volume post-operatively (p < 0.05). There was no correlation between the change in volume or post-operative CSF volumes and CCOS. The pre-operative volume of the FM-C2 was positively correlated with total CCOS (Wald [Formula: see text], [Formula: see text]) and was significantly smaller in the 0-6-year age group (2.38 ± 1.27 ml vs. 3.67 ± 1.56 ml, p = 0.014). No morphometric measurement changed significantly after surgery or demonstrated a relationship with CCOS.

CONCLUSIONS

Volumetric changes in the CSF cisterns of the posterior cranial fossa and upper cervical canal do not correlate with the age-related differences in clinical outcomes in paediatric CIM. The pre-operative volume of the FM-C2 cistern may have a role in predicting the likelihood of a beneficial post-operative outcome in paediatric CIM.

Predicting clinical outcomes using morphometric changes in adults with complex Chiari malformation undergoing occipitocervical fusion with or without ventral decompression: patient series

BACKGROUND

The authors assessed the connection between clinical outcomes and morphometrics in patients with complex Chiari malformation (CM) who have undergone posterior fossa decompression (PFD) and subsequent occipitocervical fusion (OCF) with or without ventral decompression (VD).

OBSERVATIONS

The authors retrospectively reviewed 33 patients with CM aged over 21 years who underwent PFD and OCF with or without endoscopic endonasal odontoidectomy at the authors’ institution (21 OCF only and 12 OCF + VD). Clivoaxial angle (CXA), pB-C2 (perpendicular line to the line between the basion and C2), atlantodental interval (ADI), basion-dens interval (BDI), basion-axial interval (BAI), and C1 canal diameter were measured on preoperative and approximately 3-month postoperative computed tomography or magnetic resonance imaging scans. Common symptoms included headache, paresthesia, and bulbar symptoms. Clinical improvement after surgery was observed in 78.8% of patients. CXA, ADI, and BDI all significantly increased after surgery, whereas pB-C2 and BAI significantly decreased. OCF + VD had a significantly more acute CXA and longer pB-C2 preoperatively than OCF only. Patients who clinically improved postoperatively showed the same significant morphometric changes, but those who did not improve showed no significant morphometric changes.

LESSONS

Patients showing improvement had greater corrections in skull base morphometrics than those who did not. Although there are various mutually nonexclusive reasons why certain patients do not improve after surgery, smaller degrees of morphometric correction could play a role.

Standardizing postoperative care for pediatric intradural Chiari decompressions to decrease length of stay

OBJECTIVE

Amid national and local budget crises, cutting costs while maintaining quality care is a top priority. Chiari malformation is a relatively common pediatric neurosurgical pathology, and postoperative care varies widely. The postoperative course can be complicated by pain and nausea, which can extend the hospital stay. In this study, the authors aimed to examine whether instituting a standardized postoperative care protocol would decrease overall patient hospital length of stay (LOS) as well as cost to families and the hospital system.

METHODS

A retrospective study of pediatric patients who underwent an intradural Chiari decompression with expansile duraplasty at a single institution from January 2016 to September 2019 was performed. A standardized postoperative care protocol was instituted on May 17, 2018. Pre- and postprotocol groups were primarily analyzed for demographics, LOS, and the estimated financial expense of the hospital stay. Secondary analysis included readmissions, opioid consumption, and follow-up.

RESULTS

The analysis included 132 pediatric patients who underwent an intradural Chiari decompression with expansile duraplasty. The preprotocol group included 97 patients and the postprotocol group included 35 patients. Patient age ranged from 0.5 to 26 years (mean 9.5 years). The mean LOS preprotocol was 55.48 hours (range 25.90-127.77 hours), and the mean postprotocol LOS was 46.39 hours (range 27.58-77.38 hours). The comparison between means showed a statistically significant decrease following protocol initiation (95% CI 1.87-16.31 hours, p = 0.014). In the preprotocol group, 21 of 97 patients (22%) were discharged the first day after surgery compared with 14 of 35 patients (40%) in the postprotocol group (p = 0.045). The estimated cost of one night on the pediatric neurosurgical intermediate ward was approximately $4500, which gives overall cost estimates for 100 theoretical cases of $927,800 for the preprotocol group and $732,900 for the postprotocol group.

CONCLUSIONS

By instituting a Chiari protocol, postoperative LOS was significantly decreased, which resulted in decreased healthcare costs while maintaining high-quality and safe care.

Ventral Tonsillar Herniation Predicts Headaches in Adults With Chiari Malformation

BACKGROUND

Radiographic characterization of Chiari malformation (CM) has historically focused on caudal tonsillar herniation (CH) below the foramen magnum. Previously, we published evidence linking ventral tonsillar herniation (VH) and medullary symptoms in very young children. We sought to extend that investigation by studying the radiographic and clinical significance of VH in adults diagnosed with CM.

METHODS

We retrospectively reviewed adults with cerebellar ectopia who underwent posterior fossa decompression with or without duraplasty (PFD/D) at our institution. VH was defined as tonsils crossing a line bisecting the caudal medulla at the level of the foramen magnum on axial MRI. Degree of VH was measured as distance between this bisecting line and the ventral tip of the herniated tonsil. Dorsal brainstem compression was qualitatively determined by assessing for obliteration of CSF space between the dorsal brainstem and the tonsils.

RESULTS

Out of 89 cases reviewed, 54 had some degree of VH. Compared with those without VH, the VH group was significantly older in age and more likely to also present with dorsal brainstem compression and headaches. No correlation was observed between degrees of CH and VH in the VH group. The degree of VH significantly decreased 3 months after PFD/D.

CONCLUSIONS

VH is relatively common in CM patients and might be an important independent radiographic metric to evaluate and consider as part of the decision-making process, especially in those presenting with Chiari-like symptomatology referable to the medulla but who do not meet the traditional criteria of cerebellar ectopia greater than 5 mm.

Feasibility of occipital condyle screw placement in patients with Chiari malformation type I: a computed tomography-based morphometric study

BACKGROUND

The occipital condyle (OC) screw is an alternative technique for occipitocervical fixation that is especially suitable for revision surgery in patients with Chiari malformation type I (CMI). This study aimed to investigate the feasibility and safety of this technique in patients with CMI.

METHODS

The CT data of 73 CMI patients and 73 healthy controls were retrospectively analyzed. The dimensions of OCs, including length, width, height, sagittal angle, and screw length, were measured in the axial, sagittal, and coronal planes using CT images. The OC available height was measured in the reconstructed oblique parasagittal plane of the trajectory.

RESULTS

The mean length, width, and height of OCs in CMI patients were 17.79 ± 2.31 mm, 11.20 ± 1.28 mm, and 5.87 ± 1.29 mm, respectively. All OC dimensions were significantly smaller in CMI patients compared with healthy controls. The mean screw length and sagittal angle were 19.13 ± 1.97 mm and 33.94° ± 5.43°, respectively. The mean OC available height was 6.36 ± 1.59 mm. According to criteria based on OC available height and width, 52.1% (76/146) of OCs in CMI patients could safely accommodate a 3.5-mm-diameter screw.

CONCLUSIONS

The OC screw is feasible in approximately half of OCs in CMI patients. Careful morphometric analyses and personalized surgical plans are necessary for the success of this operation in CMI patients.

Pathogenesis and Classification of Chiari Malformation Type I Based on the Mechanism of Ptosis of the Brain Stem and Cerebellum: A Morphometric Study of the Posterior Cranial Fossa and Craniovertebral Junction

Introduction  We investigated the mechanism of ptosis of the brain stem and cerebellum (hindbrain) in Chiari malformation type I (CM-I) and classified CM-I according to pathogenesis, based on a morphometric study of the posterior cranial fossa (PCF) and craniovertebral junction (CVJ). We discuss the appropriate surgical treatment for hindbrain ptosis. Materials and Methods  We examined 500 patients with CM-I and 100 healthy control individuals. We calculated the volume of the PCF (VPCF) and measured the axial length of the enchondral parts of the occipital bone and hindbrain. As statistical analyses, for the multiple analyses, heavy palindromic tests were used. Using three independent objective parameters, we tried to classify CM-I. Results  Three independent subtypes were confirmed (CM-I types A, B, and C). CM-I type A (167 cases): normal VPCF, normal volume of the area surrounding the foramen magnum (VSFM), and normal occipital bone size; CM-I type B (178 cases): normal VPCF, small VSFM, and small occipital bone size; and CM-I type C (155 cases): small VPCF, small VSFM, and small occipital bone size. Conclusions  Morphometric analyses of PCF and CVJ were very useful for the investigation of the mechanism of hindbrain ptosis and classifying CM-I according to pathogenesis. CM-I type A included mechanisms other than hindbrain ptosis, for example, CVJ instability, tethered cord, and increased intracranial pressure. CM-I types B and C demonstrated underdevelopment of the occipital bone. For CM-I types B and C, posterior decompression should be performed. For CM-I type A, appropriate surgical management should be selected.

Surgical Management of Chiari Malformations: Preliminary Results of Surgery According to the Mechanisms of Ptosis of the Brain Stem and Cerebellum

Introduction  We classified Chiari malformation type I (CM-I) according to the mechanism of ptosis of the brain stem and cerebellum, based on a morphometric study of the posterior cranial fossa (PCF) and craniovertebral junction (CVJ). Surgery was performed to manage the mechanism of the hindbrain ptosis. Materials and Methods  We calculated the volume of the PCF (VPCF) and the area surrounding the foramen magnum (VSFM) and measured the axial length of the enchondral parts of the occipital bone (occipital bone size) and the hindbrain. According to these measures, we classified CM-I into type A (normal VPCF, normal VSFM, and normal occipital bone size), type B (normal VPCF, small VSFM, and small occipital bone size), and type C (small VPCF, small VSFM, and small occipital bone size). Foramen magnum decompression (FMD) (280 cases) was performed on CM-I types A and B. Expansive suboccipital cranioplasty (ESCP) was performed on CM-I type C. Posterior craniocervical fixation (CCF) was performed in cases with CVJ instability. Lysis of the adhesion and/or sectioning of the filum terminale were performed on cases with tethered cord syndrome. Results  Both ESCP and FMD had a high rate of improvement of neurological symptoms (87%) and recovery rate. There was only small number of complications. CCF had a high rate of improvement of neurological symptoms (88%) and joint stabilization. Conclusion  In the management of Chiari malformation, appropriate surgical methods that address ptosis of the hindbrain should be chosen. Each surgical approach resulted in a good improvement of neurological symptoms.

The 270° Circumferential Microsurgical Decompression of the Foramen Magnum in Adult Chiari Malformation Type I: Single Surgeon Series of 130 Patients with Syringomyelia, Neurologic, and Headache Outcomes

OBJECTIVE

Chiari malformation type I (CM-I) is a craniocervical junction disorder associated with descent of the cerebellar tonsils >5 mm. The prevalence of CM-I is common, including 0.5%-3.5% in the general population, 0.56%-0.77% on magnetic resonance imaging, and 0.62% in anatomic dissection studies. We sought to measure our surgical outcomes related to resolution/improvement of headaches, neurologic outcomes, and syringomyelia compared with reported adult CM-I studies from 2000-2019.

METHODS

From December 2003 to June 2018, the first author (K.I.A.) performed 270° circumferential decompression on adult (>18 years) patients with CM-I. At admission and follow-up, all parameters were numerically evaluated; headaches were self-reported on the visual analog scale, neurologic condition was evaluated using Karnofsky Performance Status and European Myelopathy Score, and syrinx width (if present) was measured on magnetic resonance imaging by grades I-IV. All parameters were analyzed, compared, and statistically tested. We compared results with our previously reported and updated systematic review of operative adult CM-I studies (studies from 2000 to 2019).

RESULTS

In our series, 118/121 (98%) experienced headache improvements and 100% experienced neurologic improvements. Complete syrinx resolution was experienced by 35/43 (81%); 8 (19%) showed significant improvement. In data from reported studies (2000-2019), only 79% experienced headache resolution, 77% improvement of neurologic status, and 74% resolution/improvement of syrinx (mean).

CONCLUSIONS

Our modified 270° circumferential microsurgical foramen magnum decompression for adult CM-I appears to be beneficial in improvement of outcomes, namely in resolution of the syrinx, neurologic symptoms, and headaches. We also confirm the association of body mass index with CM-I. Further studies are needed to confirm our results.

The Perplexity Surrounding Chiari Malformations - Are We Any Wiser Now?

Chiari malformations are a diverse group of abnormalities of the brain, craniovertebral junction, and the spine. Chiari 0, I, and 1.5 malformations, likely a spectrum of the same malformation with increasing severity, are due to the inadequacy of the para-axial mesoderm, which leads to insufficient development of occipital somites. Chiari II malformation is possibly due to nonclosure of the caudal end of the neuropore, with similar pathogenesis in the rostral end, which causes a Chiari III malformation. There have been significant developments in the understanding of this complex entity owing to insights into the pathogenesis and advancements in imaging modalities and neurosurgical techniques. This article aims to review the different types and pathophysiology of the Chiari malformations, along with a description of the various associated abnormalities. We also highlight the role of ante- and postnatal imaging, with a focus on the newer techniques in the presurgical evaluation, with a brief mention of the surgical procedures and the associated postsurgical complications.

Chiari type 1-a malformation or a syndrome? A critical review

OBJECTIVE

As the understanding of pathophysiology behind Chiari malformation still is limited, the treatment of Chiari malformation type 1 remains rather empirical. This may result in suboptimal treatment strategy and outcome in many cases. In this review, we critically address whether the condition known today as Chiari malformation type I should rather be denoted Chiari syndrome.

METHODS

The current knowledge of Chiari malformation type 1 is summarized from the historical, etymological, genetic, clinical, and in particular pathophysiological perspectives.

RESULTS

There are several lines of evidence that Chiari malformation type 1 represents a condition significantly different from types 2 to 4. Unlike the other types, the type 1 should rather be considered a syndrome, thus supporting the reasons to reappraise the traditional classification of Chiari malformations.

CONCLUSION

We propose that Chiari malformation type 1 should rather be denoted Chiari syndrome, while the notation malformation is maintained for types 2-4.

Clivus length distinguishes between asymptomatic healthy controls and symptomatic adult women with Chiari malformation type I

PURPOSE

While the presence of cerebellar tonsillar descent in radiological images has been used as evidence of Chiari malformation type I (CMI), tonsillar ectopia alone is insufficient to identify individuals with symptomatic CMI. This study sought to identify differences in brain morphology between symptomatic CMI and healthy controls in adult females.

METHODS

Two hundred and ten adult females with symptomatic CMI and 90 age- and body mass index-matched asymptomatic female controls were compared using seven brain morphometric measures visible on magnetic resonance images. The CMI and control groups were divided into four subgroups based on the tonsillar position (TP) relative to the foramen magnum: group 1 was made up of healthy controls with normal TP (TP < 0 mm); group 2 was comprised of control individuals with low-lying TP (1-5 mm); group 3 was comprised of symptomatic CMI patients with low-lying TP (1-5 mm); group 4 contained symptomatic CMI patients with severe tonsillar descent (6-13 mm).

RESULTS

All morphometrics for symptomatic CMI with severe tonsillar descent were significantly different than those for both control groups. The CMI group with low-lying TP was significantly different for four measures when compared to controls with normal TP. However, only clivus length was statistically different between the CMI and healthy control groups with low-lying TP.

CONCLUSION

This study demonstrates that clivus length distinguishes adult female healthy individuals with low-lying tonsils from those with symptomatic CMI. Further investigation is required to understand the importance of a shorter clivus length on CMI symptomatology and pathophysiology.

Posterior Fossa Dimensions of Chiari Malformation Patients Compared with Normal Subjects: Systematic Review and Meta-Analysis

BACKGROUND

Chiari malformation (CM) is defined as a herniation of cerebellar tonsils below the foramen magnum and is considered to be due to underdevelopment of posterior fossa (PF) bone components. There is overcrowding of neural structures, and normal cerebrospinal fluid circulation is frequently blocked. Although several publications exist of measurements of dimensions and volumes from bone components of PF in CM, there is no systematic review evaluating quantitatively these dimensions. The aim of this study was to evaluate PF dimensions and volumes in a meta-analysis.

METHODS

An electronic search using PubMed and Google Scholar was done. Study eligibility criteria were defined by the PICO strategy, which selected patients and interventions. Studies comparing PF dimensions between patients with CM and normal subjects were selected. A meta-analysis of pooled data was done using statistical software.

RESULTS

Data for pooled analysis were obtained from 12 studies. Data synthesis was based on small published sample sizes in the majority of studies. Key findings included smaller measurements of clivus, supraoccipital bone, and PF area dimensions in patients with CM compared with normal subjects. Brainstem and cerebellar length was not different between groups.

CONCLUSIONS

This review provides evidence of smaller measurements of clivus, supraoccipital bone, and PF area dimensions in patients with CM compared with normal subjects. An implication of the key findings is that surgical treatment of CMs should consider the smaller dimensions of PF in planning.

Three-Dimensional CT Morphometric Image Analysis of the Clivus and Sphenoid Sinus in Chiari Malformation Type I

This study evaluated three-dimensional (3D) volumetric image reconstructions to identify morphological differences of the clivus and sphenoid sinus on computed tomography (CT) scans of Chiari malformation type I (CMI) and control subjects. Axial CT images of adult females for 30 CMI subjects and 30 age and body mass index (BMI) matched controls were used for this retrospective study. 3D volumetric reconstructions were created from the bone windows of axial data following image registration for position and orientation correction of the head. The volume, surface area, linear dimensions and spatial position in the x, y, and z-axes were computed separately for the clivus and the sphenoid sinus for each subject. Eleven parameters were found to be significantly different between CMI subjects compared to controls. Most notably, clivus volume was reduced by 31% on average in CMI subjects. In contrast, we found that the sphenoid sinus volume was 38% greater on average in CMI subjects. Moreover, clivus length, height, width, and thickness were 3.7, 2.8, 3.0 and 9.4 mm reduced, respectively, in CMI subjects. This is the first study to demonstrate cephalometric differences in the 3D morphology of the clivus and sphenoid sinus between CMI subjects and controls.

Defining, diagnosing, clarifying, and classifying the Chiari I malformations

PURPOSE

Chiari malformations (CM) have been traditionally classified into four categories: I, II, III, and IV. In light of more recent understandings, variations of the CM have required a modification of this classification.

METHODS

This article discusses the presentation, diagnostics, and treatment of the newer forms of hindbrain herniation associated with the CM type I.

RESULTS

The CM 1 is a spectrum that includes some patients who do not fall into the exact category of this entity.

CONCLUSIONS

While CM have been categorically recognized as discrete and individual conditions, newer classifications such as CM 0 and CM 1.5 exhibit some degree of continuity with CM 1; however, they require distinct and separate classification as symptoms and treatments can vary among these clinical subtypes.

Onset and Resolution of Chiari Malformations and Hydrocephalus in Syndromic Craniosynostosis following Posterior Vault Distraction

BACKGROUND

Patients with syndromic craniosynostosis have an increased incidence of progressive hydrocephalus and Chiari malformations, with few data on the relative benefit of various surgical interventions. The authors compare the incidence and resolution of Chiari malformations and hydrocephalus between patients undergoing posterior vault distraction osteogenesis (PVDO) and patients undergoing conventional cranial vault remodeling.

METHODS

Patients with syndromic craniosynostosis who underwent cranial vault surgery from 2004 to 2016 at a single academic hospital, with adequate radiographic assessments, were reviewed. Demographics, interventions, the presence of a Chiari malformation on radiographic studies and hydrocephalus requiring shunt placement were recorded. Mann-Whitney U and Fisher's exact tests were used as appropriate.

RESULTS

Forty-nine patients underwent PVDO, and 23 patients underwent cranial vault remodeling during the study period. Median age at surgery (p = 0.880), sex (p = 0.123), and types of syndrome (p = 0.583) were well matched. Patients who underwent PVDO had a decreased incidence of developing Chiari malformations postoperatively compared with the cranial vault remodeling cohort (2.0 percent versus 17.4 percent; p = 0.033). Not surprisingly, no significant difference was found between the groups with regard to the incidence of postoperative hydrocephalus requiring shunt placement (PVDO, 4.1 percent; cranial vault remodeling, 4.3 percent; p = 0.999).

CONCLUSIONS

As expected, PVDO did not significantly affect intracranial hydrodynamics to the extent that hydrocephalus shunting rates were different for patients with syndromic craniosynostosis. However, PVDO was associated with a reduced risk of developing a Chiari malformation; however, prospective evaluation is needed to determine causality.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, III.

Chiari type I and hydrocephalus

PURPOSE

The association between Chiari type I malformation (CIM) and hydrocephalus raises a great interest because of the still unclear pathogenesis and the management implications. The goal of this paper is to review the theories on the cause-effect mechanisms of such a relationship and to analyze the results of the management of this condition.

METHODS

A review of the literature has been performed, focusing on the articles specifically addressing the problem of CIM and hydrocephalus and on the series reporting about its treatment. Also, the personal authors' experience is briefly discussed.

RESULTS

As far as the pathogenesis is concerned, it seems clear that raised intracranial pressure due to hydrocephalus can cause a transient and reversible tonsillar caudal ectopia ("pressure from above" hypothesis), which is something different from CIM. A "complex" hypothesis, on the other hand, can explain the occurrence of hydrocephalus and CIM because of the venous engorgement resulting from the hypoplasia of the posterior cranial fossa (PCF) and the occlusion of the jugular foramina, leading to cerebellar edema (CIM) and CSF hypo-resorption (hydrocephalus). Nevertheless, such a mechanism can be advocated only in a minority of cases (syndromic craniosynostosis). In non-syndromic CIM subjects, the presence of hydrocephalus could be explained by an occlusion of the basal CSF pathways, which would occur completely in a minority of cases (only 7-10% of CIM patients show hydrocephalus) while it would be partial in the remaining cases (no hydrocephalus). This hypothesis still needs to be demonstrated. As far as the management is concerned, the strategy to treat the hydrocephalus first is commonly accepted. Because of the "obstructive" origin of CIM-related hydrocephalus, the use of endoscopic third ventriculostomy (ETV) is straightforward. Actually, the analysis of the literature, concerning 63 cases reported so far, reveals very high success rates of ETV in treating hydrocephalus (90.5%), CIM (78.5%), and syringomyelia symptoms (76%) as well as in giving a radiological improvement of both CIM (74%) and syringomyelia (89%). The failures of ETV were not attributable to CIM or syringomyelia. Only 11% of cases required PCF decompression after ETV.

CONCLUSIONS

The association between CIM and hydrocephalus probably results from different, multifactorial, and not yet completely understood mechanisms, which place the affected patients in a peculiar subgroup among those constituting the heterogeneous CIM population. ETV is confirmed as the best first approach for this subset of patients.

Bony decompression vs duraplasty for Chiari I malformation: does the eternal dilemma matter?

PURPOSE

The management of Chiari I malformation (CIM) still raises the problem of the optimal surgical treatment, with special regard to the "eternal dilemma" of the posterior fossa bony decompression alone (PFBD) or with duraplasty (PFBDD). The goal of the present review is to update the results (outcome and complications) of both techniques to better understand the correct indication for each of them.

METHODS

A review of the literature has been performed, focusing on the articles and the meta-analyses specifically addressing the problem of PFBD vs PFBDD. Also, the personal authors' experience is briefly discussed.

RESULTS

PFBD (usually with C1 laminectomy, often with delamination of the external dural layer) is the most commonly used technique in children, especially if syringomyelia is absent. It ensures a high success rate, with > 80% clinical improvement and about 75% reduction of the syringomyelia, and a very low risk of complications, hospital stay, and costs. A certain risk of recurrence is present (2-12%). PFBDD (with autologous tissues or dural substitutes), on the other hand, is mostly used not only in adults but also in children with large syringomyelia. It is burdened by a higher risk of complications (namely, the CSF-related ones), longer hospital stay, and higher costs; however, it warrants a better clinical improvement (> 85%) and a lower risk of reoperation (2-3.5%). Eight meta-analyses of the literature (three on pediatric series and five in adult series) and one prospective study in children, published in the last decade, largely confirm these findings.

CONCLUSION

PFBD and PFBDD are different techniques that are indicated for different types of patients. In children, PFBD has been demonstrated to represent the best choice, although some patients may require a more aggressive treatment. Therefore, the success in the management of CIM, with or without syringomyelia, depends on the correct indication to surgery and on a patient-tailored choice rather than on the surgical technique.

Comparative Volumetric Analysis of the Brain and Cerebrospinal Fluid in Chiari Type I Malformation Patients: A Morphological Study

BACKGROUND

Chiari Type I malformation (CM-I) is defined as the migration of cerebellar tonsils from the foramen magnum in the caudal direction and is characterized by the disproportion of the neural structures. The aim of this study was to investigate the brain volume differences between CM-I patients and normal population using a comparative volumetric analysis.

METHODS

140 patients with CM-I and 140 age- and sex-matched healthy controls were included in this study. The magnetic resonance imaging (MRI) data of both groups were analyzed with an automated MRI brain morphometry system. Total intracranial, cerebrum, cerebellum, brainstem, cerebrospinal fluid (CSF), and lateral ventricle volumes as well as cerebrum and cerebellum gray/white matter (GM/WM) volumes were measured. Statistical analysis was performed.

RESULTS

Both total CSF and lateral ventricle volumes and volume percentages (Pct) were found significantly higher in CM-I patients compared to the control group. However, there were significant decreases in cerebrum and cerebellum volume Pct in CM-I patients. Although there were no significant differences in cerebrum WM volumes and volume Pct, cerebrum GM volume Pct were found to be significantly lower in CM-I patients.

CONCLUSIONS

Revealing the increased CSF and lateral ventricle volume, and volume Pct supported concomitant ventricular enlargement and hydrocephalus in some CM-I patients. Decreased cerebrum GM volume Pct compared to the control group might be the underlying factor of some cortical dysfunctions in CM-I patients.

Fourth Ventricle Enlargement in Chiari Malformation Type I

OBJECTIVE

How Chiari malformation type I (CM-I) affects posterior fossa brain structures and produces various symptoms remains unclear. The fourth ventricle is surrounded by critical structures required for normal function. The foramen of Magendie can be obstructed in CM-I; therefore, fourth ventricle changes may occur. To test this hypothesis, we assessed fourth ventricle volume in CM-I compared with healthy controls.

METHODS

Using our database from 2007-2016, we studied 72 patients with CM-I and 30 age-matched healthy control subjects. Fourth and lateral ventricle volumes and posterior fossa volumes (PFV) were assessed and correlated with clinical signs and symptoms. Statistical analysis was performed.

RESULTS

Patients with CM-I had larger fourth ventricle volumes compared with control subjects (1.31 vs. 0.95 mL; P = 0.012). There were no differences in lateral ventricle volume or PFV. CM-I fourth ventricle volume was associated with tonsillar descent (P = 0.030). CM-I fourth ventricle volume variance was larger than healthy controls (F_71,29 = 8.33; P < 0.0001). Patients with CM-I with severe signs and symptoms had a significantly larger fourth ventricle than patients with CM-I with mild signs and symptoms (1.565 vs. 1.015 mL; P = 0.0002).

CONCLUSIONS

The fourth ventricle can be enlarged in CM-I independent of lateral ventricle size and is associated with greater tonsillar descent. Most importantly, fourth ventricle enlargement was associated with a worse clinical and radiographic presentation independent of PFV. Fourth ventricle enlargement can affect critical structures and may be a mechanism contributing to symptoms unexplained by tonsil descent. Fourth ventricle enlargement is a useful adjunct in assessing CM-I.

Quantification of changes in brain morphology following posterior fossa decompression surgery in women treated for Chiari malformation type 1

PURPOSE

While 84% of patients surgically treated for Chiari malformation type 1 (CM1) demonstrate improved quality of life after posterior fossa decompression surgery, there are many risks associated with this surgery. Surgical planning to identify candidates likely to improve postoperatively may benefit from an improved understanding of morphological changes after decompression surgery. To evaluate these changes, we quantified 59 morphological parameters on 42 CM1 adult female patients before and after CM1 decompression surgery.

METHODS

Fifty-nine morphological parameters in the posterior cranial fossa, cranio-cervical, and intracranial regions in the midsagittal plane were evaluated using 42 T1-weighted magnetic resonance images of female CM1 patients before and after surgery, and 42 healthy female controls. Morphological differences before and after surgery were compared through the development of a technique to establish the opisthion location, a key reference point not present after surgery.

RESULTS

In addition to the expected reduction of the cranio-caudal dimension of the cerebellum, objective analyses showed a significant increase in the area of the cerebrospinal fluid spaces, posterior (6×) and inferior (2.6×) to the cerebellum (+ 112 ± 102 and + 140 ± 127 mm2, respectively). This increased area was primarily impacted by an average reduction in the occipital bone length of 24.5 ± 7.3 mm following surgery. Based on multiple angles, results demonstrated a 2°-4° anterior rotation of the cerebellum after surgery.

CONCLUSION

Our results show that decompression surgery results in significant changes in the cerebellum and cerebrospinal fluid spaces. Further investigation should determine how these morphological changes impact clinical outcomes.

Small posterior fossa in Chiari I malformation affected families is significantly linked to 1q43-44 and 12q23-24.11 using whole exome sequencing

The posterior fossa of the cranium contains the cerebellum and brainstem. Processes that reduce the volume of the posterior fossa squeeze the cerebellum and brainstem caudally, resulting in Chiari I malformation (CM1). CM1 causes neck pain, balance issues, decreased motor skills and headaches in those affected. We have posterior fossa measurements and whole exome sequence data on individuals from 7 extended families from Russia that have a family history of CM1. We performed parametric linkage analyses using an autosomal dominant inheritance model with a disease allele frequency of 0.01 and a penetrance of 0.8 for carriers and 0.0 for non-carriers. Variant-based two-point linkage analysis and gene-based linkage analysis was performed. Our results found a genome-wide significant signal on chromosome 1q43-44 (max HLOD = 3.3) in the variant-based analysis and 12q23 (max HLOD = 4.2) in the gene-based analysis. In both cases, the signal was driven by a single (different) family that contained a long, linked haplotype across the region in question. Using functional annotation, we were able to identify several rare nonsynonymous variants that were enriched in each family. The best candidate genes were rs765865412:G>A in MYBPC1 for the 12q haplotype and rs61749963:A>G in COX20 for the 1q haplotype. Good candidate variants in the 1q haplotype were also identified in CEP170 and AKT. Further laboratory work is planned to verify the causality of these genes.

Can the Etiopathogenesis of Chiari Malformation Be Craniocervical Junction Stabilization Difference? Morphometric Analysis of Craniocervical Junction Ligaments

OBJECTIVE

The craniocervical junction permits a certain amount of mobility for the cervical spine. The biomechanical properties of occipital bone-atlas joint mainly depend on the bony structure, and atlas-axis joint biomechanical properties mainly depend on ligamentous structure. The underlying etiologic factor of Chiari malformation (CM) is debatable. Nowadays, some researchers argue that stabilization difference is one of the suspicious factors for etiopathogenesis. We aim to analyze the ligamentous morphometric differences of CM.

METHODS

Magnetic resonance images of 93 adult healthy subjects (n = 93) without any craniocervical junction development abnormalities and 25 (n = 25) adult patients with craniocervical junction development abnormalities (Arnold CM) were evaluated. Length, width, and length-width ratios of ligaments were evaluated.

RESULTS

Length of transverse ligament (mean: 23 ± 3.6 [range: 12.1-31.4]) in the normal population was significantly longer than transverse ligament length in CM patients (mean: 21.3 ± 2.5 [range: 17.2-24.9]). Length of alar ligament (mean: 10.7 ± 2 [range: 5.1-15.4]) in the normal population was significantly longer than alar ligament length in CM patients (mean: 8.8 ± 3.8 [range: 1.1-16.6]) (P = 0.007).

CONCLUSIONS

Craniocervical ligaments play an important role in maintaining stability and motion capacity of this region. This study promoted better understanding of craniocervical junction anomalies and provided data that facilitate performing more precise surgical treatment.

The Incidence of Chiari Malformations in Patients with Isolated Sagittal Synostosis

Background:

We report the incidence of Chiari malformation I (CMI) in a cohort of 377 patients with isolated sagittal synostosis (ISS), which is to the best of our knowledge the largest such series reported to date.

Methods:

A retrospective review of patients seen at a single institution from 2007 to 2017 was completed. ISS, Chiari malformations (CMI and CMII) and hydrocephalus were diagnosed by a senior neuroradiologist (G.Z.). Patients who met the inclusion criteria were divided into early (group A) and late (group B) presenting groups, as well as operated (group I) and unoperated (group II) groups. The patients were further subdivided into group AI (early operated), group AII (early unoperated), group BI (late operated), and group BII (late unoperated). Once identified, patient notes were examined for the following data sets: date of birth, age of presentation, age at last follow-up, other systemic conditions as well as molecular testing results. Surgical interventions, ophthalmological, and other relevant data were recorded. Statistical analysis was run in the form of a chi-square test to identify a significant difference between each subgroup. A literature review of the incidence of Chiari malformations in patients with ISS was conducted.

Results:

Three hundred seventy-seven patients constitute the study’s total cohort (272 were males and 105 females). This cohort was divided into patients who underwent surgical repair of ISS (group 1: n = 200), and patients who did not (group 2: n = 177). The entire cohort was also divided into early (group A: n = 161) and late (group B: n = 216) presenting craniosynostosis. In the total cohort, 22/377 (5.8%) patients with CMI were identified. CMI was found in 14/200 (7.0%) patients in group I, and 8/177 (4.5%) patients in group II. CMI was found in 2/161 (1%) patients in group A, and 20/216 (9.2%) patients in group B. The incidence of CMI in group AI (early operated) was 2/151 (1.3%), in group AII (early unoperated) was 0/10, in group BI (late operated) was 11/49 (21%), and in group BII (late unoperated) was 9/167 (5.4%). Chi-square analysis revealed a significant difference between the incidence of CMI in the early-presenting (group A) and late-presenting (group B) groups (P = 0.001) and between the late-presenting operated (BI) and late-presenting unoperated (BII) groups (P = 0.001). The incidence of hydrocephalus was 1.6% (6/377) in the total cohort. However, all patients diagnosed with hydrocephalus came from group II (no surgical ISS correction). The incidence of hydrocephalus in group II was 3.3% (6/177). The incidence of hydrocephalus in group BII (late unoperated ISS) was 3.0% (5/167). The incidence of hydrocephalus in group AII (early unoperated ISS) was 9.0% (1/11).

Conclusions:

We noted the highest incidence of CMI—21%—in group BI (late-presenting operated). We noted hydrocephalus in group II (nonoperated), with the highest incidence of hydrocephalus found in the group BII (late-presenting unoperated) subgroup. We therefore recommend patients with ISS receive funduscopic examination to screen for raised intracranial pressure (ICP) associated with CMI and hydrocephalus, especially patients with late-presenting ISS.