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

Quantification of Cerebellar Crowding in Type I Chiari Malformation

This study was focused on a semi-automated morphometric analysis of the cerebellum in the mid-sagittal plane as an alternative to tonsillar descent alone in the evaluation of Chiari malformation type 1 (CMI) patients. Morphometric analyses of posterior fossa structures were performed on mid-sagittal MRI images of 375 individuals (females, > 18 years, 235 CMI and 140 healthy controls). Twenty-six parameters including linear, angular and area measurements together with non-dimensional ratios were calculated. Eighteen parameters were found to be significantly different between CMI and control subjects. Smaller posterior cranial fossa (PCF) area in CMI subjects was attributed to a smaller PCF area anterior to the brainstem. The cerebellar area was found to be larger in CMI subjects as compared to controls (15.1%), even without inclusion of the tonsillar area below the foramen magnum (FM) (8.4%). The larger cerebellar area in CMI subjects was due to cranial-caudal elongation of the cerebellum, predominately below the fastigium. The cerebrospinal fluid spaces below the FM were smaller in CMI subjects as compared to controls. Overall, greater cerebellar crowding was identified in CMI subjects relative to healthy controls. These observations may improve our understanding of the pathophysiology of CMI in adult female patients.

Sequential Enlargement of Posterior Fossa After Duraplasty for Chiari Malformation Type 1

Objective

There are several material options for duraplasty in surgery for foramen magnum decompression (FMD). We retrospectively analyzed surgical results and the impact of sequential alteration of posterior fossa (PF) size in patients with Chiari malformation type 1 after duraplasty using local fascia.

Methods

The patients with Chiari malformation type 1 who underwent FMD with duraplasty using local fascia at our institution between 2004 and 2015 were included in the study. Some pediatric patients who underwent FMD without duraplasty and patients with insufficient follow-up data were excluded. Improvement of clinical signs, regression of syrinx, and temporal alteration of PF size were analyzed with perioperative magnetic resonance imaging. Postoperative clinical outcomes were evaluated at the final follow-up using the Chicago Chiari Outcome Scale. Correlations between the PF size alteration and size of dural patch or Chicago Chiari Outcome Scale were statistically analyzed.

Results

Twelve patients were included in this study. The mean age of the patients was 31.9 (range, 18–48) years. Syrinx was incorporated in 11 patients and regressed postoperatively in all patients. The PF was significantly enlarged sequentially over time (P < 0.05). The degree of enlargement was positively correlated with size of the fascial patch (r = 0.540). Postoperative clinical outcomes at final follow-up were positively correlated with the degree of PF enlargement (r = 0.678).

Conclusions

The PF was enlarged sequentially over time after duraplasty using local fascia. The degree of enlargement was positively correlated with the size of the fascial patch and the likelihood of a favorable postoperative outcome.

Surgical Treatment of Chiari Malformation in Adults: Comparison of Surgical Techniques Described in the Literature and Our Experience

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Autologous cervical fascia duraplasty in 123 children and adults with Chiari malformation type I: surgical technique and complications

OBJECT Techniques for combined extradural and intradural decompression with expansile duraplasty for Chiari malformation type I (CM-I) have been well described, with various allogenic and autologous materials used for duraplasty. However, the approach and surgical technique used for duraplasty in our treatment of CM-I and developed by the senior author in the 1990s has not been described. METHODS A prospective database was initiated in March 2003 to denote the use of cervical fascia for duraplasty and incorporate an ongoing detailed record of complications during the surgical treatment of children and adults with CM-I with and without syringomyelia. A total of 389 surgeries for CM-I were performed on 379 patients from March 2003 to June 2016. A total of 123 posterior procedures were performed on 123 patients in which both a posterior fossa extradural and intradural decompression with duraplasty (extra-intradural) was performed. In this paper the authors describe the surgical technique for harvesting and using cervical fascia for duraplasty in the surgical treatment of CM-I and analyze and discuss complications from a prospective database spanning 2003-2016. RESULTS The authors found that cervical fascia can be harvested in patients of all ages (2-61 years old) without difficulty, and it provides a good substitute for dura in creating an expansile duraplasty in patients with CM-I. Cervical fascia is an elastic-like material with a consistency that allows for a strong watertight closure. Harvesting the cervical fascia graft does not require any further extension of the incision superiorly or inferiorly to obtain the graft. Complications were uncommon in this study of 123 children and adults. The risk of any type of complication (aseptic meningitis, CSF leak, pseudomeningocele, infection, development of hydrocephalus, and need for ventriculoperitoneal shunt) for the 78 patients in the pediatric age group was 0%. The risk of complication in the adult group was 6.7% (1 patient with aseptic meningitis and 2 patients with CSF leak). CONCLUSIONS Autologous cervical fascia is easy to obtain in patients of all ages and provides an effective material for duraplasty in the treatment of CM-I. Complications from the combination of both an extradural and intradural decompression with autologous cervical fascia duraplasty are uncommon.

Spontaneous Intracranial Hypotension: 10 Myths and Misperceptions

OBJECTIVE

To discuss common myths and misperceptions about spontaneous intracranial hypotension (SIH), focusing on common issues related to diagnosis and treatment, and to review the evidence that contradicts and clarifies these myths.

BACKGROUND

Recognition of SIH has increased in recent years. With increasing recognition, however, has come an increased demand for management by neurologists and headache specialists, some of whom have little prior experience with the condition. This dearth of practical experience, and lack of awareness of recent investigations into SIH, produces heterogeneity in diagnostic and treatment pathways, driven in part by outdated, confusing, or unsubstantiated conceptions of the condition. We sought to address this heterogeneity by identifying 10 myths and misperceptions that we frequently encounter when receiving referrals for suspected or confirmed SIH, and to review the literature addressing these topics.

METHODS

Ten topics relevant to diagnosis and treatment SIH were generated by the authors. A search for studies addressing SIH was conducted using PubMed and EMBASE, limited to English language only, peer reviewed publications from inception to 2018. Individual case reports were excluded. The resulting studies were reviewed for relevance to the topics in question.

RESULTS

The search generated 557 studies addressing SIH; 75 case reports were excluded. Fifty-four studies were considered to be of high relevance to the topics addressed, and were included in the data synthesis. The topics are presented in the form of a narrative review.

CONCLUSIONS

The understanding of SIH has evolved over the recent decades, leading to improvements in knowledge about the pathophysiology of the condition, diagnostic strategies, and expanded treatments. Awareness of these changes, and dispelling outdated misconceptions about SIH, is critical to providing appropriate care for patients and guiding future investigations going forward.

Developments in the treatment of Chiari type 1 malformations over the past decade

Background

Chiari malformations type 1 (CM-1), a developmental anomaly of the posterior fossa, usually presents in adolescence or early adulthood. There are few studies on the national incidence of CM-1, taking into account outcomes based on concurrent diagnoses. To quantify trends in treatment and associated diagnoses, as retrospective review of the Kid's Inpatient Database (KID) from 2003-2012 was conducted.

Methods

Patients aged 0-20 with primary diagnosis of CM-1 in the KID database were identified. Demographics and concurrent diagnoses were analyzed using chi-squared and t-tests for categorical and numerical variables, respectively. Trends in diagnosis, treatments, and outcomes were analyzed using analysis of variance (ANOVA).

Results

Five thousand four hundred and thirty-eight patients were identified in the KID database with a primary diagnosis of CM-1 (10.5 years, 55% female). CM-1 primary diagnoses have increased over time (45 to 96 per 100,000). CM-1 patients had the following concurrent diagnoses: 23.8% syringomyelia/syringobulbia, 11.5% scoliosis, 5.9% hydrocephalus, 2.2% tethered cord syndrome. Eighty-three point four percent of CM-1 patients underwent surgical treatment, and rate of surgical treatment for CM-1 increased from 2003-2012 (66% to 72%, P<0.001) though complication rate decreased (7% to 3%, P<0.001) and mortality rates remained constant. Seventy percent of surgeries involved decompression-only, which increased neurologic complications compared to fusions (P=0.039). Cranial decompressions decreased from 2003-2012 (42.2-30.5%) while spinal decompressions increased (73.1-77.4%). Fusion rates have increased over time (0.45% to 1.8%) and are associated with higher complications than decompression-only (11.9% vs. 4.7%). Seven point four percent of patients experienced at least one peri-operative complication (nervous system, dysphagia, respiratory most common). Patients with concurrent hydrocephalus had increased; nervous system, respiratory and urinary complications (P<0.006) and syringomyelia increased the rate of respiratory complications (P=0.037).

Conclusions

CM-1 diagnoses have increased in the last decade. Despite the decrease in overall complication rates, fusions are becoming more common and are associated with higher peri-operative complication rates. Commonly associated diagnoses including syringomyelia and hydrocephalus, can dramatically increase complication rates.

Imaging of Congenital Malformations

PURPOSE OF REVIEW

Intracranial congenital malformations are anomalies of brain development caused by genetic and environmental influences. This article discusses common intracranial congenital malformations, presents the associated neuroimaging findings, and discusses how appropriate identification of intracranial anomalies can impact diagnosis and treatment.

RECENT FINDINGS

Advances in neuroimaging techniques and genetic research have led to a better understanding of the pathogenesis of many congenital malformations, adding insight into their clinical relevance and the intricate relationship between critical periods of development, genetic predisposition, and environmental insults. When one malformation is discovered, a high likelihood of more malformations exists. In some instances, the intracranial anomalies will lead to the diagnosis of a particular neurologic syndrome, which may, in turn, lead to modification of a plan of care.

SUMMARY

Knowledge of congenital malformations and their appearance on imaging sequences is essential to improve clinical outcomes and quality of life for patients.

Intradural pathology and pathophysiology associated with Chiari I malformation in children and adults with and without syringomyelia

OBJECTIVE The pathophysiology underlying tonsillar herniation and CSF obstruction in Chiari malformation Type I (CM-I) is unclear, and the cause of CM-I-associated syringomyelia is not well understood. A better understanding of this pathophysiology is important for an improved treatment strategy. Therefore, the authors sought to identify, characterize, and examine the intradural pathology and CSF flow pathophysiology in the posterior fossa and at the level of the foramen magnum that occurs in the setting of CM-I. They determined the incidence of these intradural findings and assessed differences across age, with the degree of tonsillar herniation, and in the presence and absence of syringomyelia. METHODS A prospective database initiated in March 2003 recorded all intraoperative findings during surgical treatment of children and adults with CM-I with or without syringomyelia. A total of 389 surgeries for CM-I were performed in 379 patients between March 2003 and June 2016. A total of 109 surgeries were performed in 109 patients with CM-I (without osseoligamentous abnormalities) in whom both a posterior fossa extradural and intradural decompression with duraplasty was performed (first-time intradural procedures). Using a surgical microscope, intradural pathology and obstruction of CSF channels were identified and assessed. Student t-tests and Fisher's exact tests compared groups in a series of univariate analyses, followed by multivariate logistic regression. RESULTS The following intradural pathological entities were observed (prevalence noted in parentheses). These include those that did not obstruct CSF flow channels: opacified arachnoid (33.0%), thickened arachnoid (3.7%), ischemic and gliotic tonsils (40.4%), tonsillar cysts (0.9%), and inferior descent of the fourth ventricle and cervicomedullary junction (CMJ) (78.0%). The following intradural pathological entities were observed to obstruct CSF flow channels: medialized tonsils (100%), tonsil overlying and obstructing the foramen of Magendie (21.1%), intertonsillar and tonsil to CMJ arachnoid adhesions (85.3%), vermian posterior inferior cerebellar artery branches obstructing the foramen of Magendie (43.1%), and arachnoid veils or webs obstructing or occluding the foramen of Magendie (52.3%). Arachnoid veils varied in type and were observed in 59.5% of patients with CM-I who had syringomyelia, which was significantly greater than the 33.3% of patients with CM-I without syringomyelia who had an arachnoid veil (p = 0.018). The presence of CM-I with an arachnoid veil had 3.22 times the odds (p = 0.013, 95% CI 1.29-8.07, by multivariate logistic regression) of being associated with syringomyelia, adjusting for tonsillar herniation. The inferior descent of the fourth ventricle and CMJ occurred with a greater degree of tonsillar herniation (p < 0.001) and correlated with a cervicomedullary kink or buckle on preoperative MRI. CONCLUSIONS Intradural pathology associated with CM-I with or without syringomyelia exists in many forms, is more prevalent than previously recognized in patients of all ages, and may play a role in the pathophysiology of CM-I tonsillar herniation. Arachnoid veils appear to partially obstruct CSF flow, are significantly more prevalent in cases of CM-I with syringomyelia, and therefore may play a role in the pathophysiology of CM-I-associated syringomyelia.

A points-based algorithm for prognosticating clinical outcome of Chiari malformation Type I with syringomyelia: results from a predictive model analysis of 82 surgically managed adult patients

OBJECTIVE Although various predictors of postoperative outcome have been previously identified in patients with Chiari malformation Type I (CMI) with syringomyelia, there is no known algorithm for predicting a multifactorial outcome measure in this widely studied disorder. Using one of the largest preoperative variable arrays used so far in CMI research, the authors attempted to generate a formula for predicting postoperative outcome. METHODS Data from the clinical records of 82 symptomatic adult patients with CMI and altered hindbrain CSF flow who were managed with foramen magnum decompression, C-1 laminectomy, and duraplasty over an 8-year period were collected and analyzed. Various preoperative clinical and radiological variables in the 57 patients who formed the study cohort were assessed in a bivariate analysis to determine their ability to predict clinical outcome (as measured on the Chicago Chiari Outcome Scale [CCOS]) and the resolution of syrinx at the last follow-up. The variables that were significant in the bivariate analysis were further analyzed in a multiple linear regression analysis. Different regression models were tested, and the model with the best prediction of CCOS was identified and internally validated in a subcohort of 25 patients. RESULTS There was no correlation between CCOS score and syrinx resolution (p = 0.24) at a mean ± SD follow-up of 40.29 ± 10.36 months. Multiple linear regression analysis revealed that the presence of gait instability, obex position, and the M-line-fourth ventricle vertex (FVV) distance correlated with CCOS score, while the presence of motor deficits was associated with poor syrinx resolution (p ≤ 0.05). The algorithm generated from the regression model demonstrated good diagnostic accuracy (area under curve 0.81), with a score of more than 128 points demonstrating 100% specificity for clinical improvement (CCOS score of 11 or greater). The model had excellent reliability (κ = 0.85) and was validated with fair accuracy in the validation cohort (area under the curve 0.75). CONCLUSIONS The presence of gait imbalance and motor deficits independently predict worse clinical and radiological outcomes, respectively, after decompressive surgery for CMI with altered hindbrain CSF flow. Caudal displacement of the obex and a shorter M-line-FVV distance correlated with good CCOS scores, indicating that patients with a greater degree of hindbrain pathology respond better to surgery. The proposed points-based algorithm has good predictive value for postoperative multifactorial outcome in these patients.

A morphometric assessment of type I Chiari malformation above the McRae line: A retrospective case-control study in 302 adult female subjects

PURPOSE

Type I Chiari malformation (CMI) is a radiologically-defined structural dysmorphism of the hindbrain and posterior cranial fossa (PCF). Traditional radiographic identification of CMI relies on the measurement of the cerebellar tonsils in relation to the foramen magnum with or without associated abnormalities of the neuraxis. The primary goal of this retrospective study was to comprehensively assess morphometric parameters above the McRea line in a group of female CMI patients and normal controls.

MATERIAL AND METHODS

Twenty-nine morphological measurements were taken on 302 mid-sagittal MR images of adult female CMI patients (n=162) and healthy controls (n=140). All MR images were voluntarily provided by CMI subjects through an online database and control participant images were obtained through the Human Connectome Project and a local hospital system.

RESULTS

Analyses were performed on the full dataset of adult female MR images and a restricted dataset of 229 participants that were equated for age, race, and body mass index. Eighteen group differences were identified in the PCF area that we grouped into three clusters; PCF structures heights, clivus angulation, and odontoid process irregularity. Fourteen group differences persisted after equating our CMI and control groups on demographic characteristics.

CONCLUSION

PCF structures reliably differ in adult female CMI patients relative to healthy controls. These differences reflect structural abnormalities in the osseous and soft tissue structures of the clivus, odontoid process, and cerebellum. Clinical and pathophysiological implications are discussed.

3D structural complexity analysis of cerebellum in Chiari malformation type I

Chiari malformation type I (CM-I), described by a descent of the cerebellar tonsils, is assumed to be a neurological developmental disorder. The aim of the present study was to investigate morphological variance in cerebellar sub-structures, including gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF), using magnetic resonance (MR) images with three-dimensional (3D) fractal dimension (FD) analysis in patients with CM-I. MRI data of 16 patients and 15 control subjects were obtained, and structural complexity analyses were performed using a box-counting FD algorithm. Results showed that patients with CM-I had significantly reduced FD values for WM and CSF in comparison with controls, and statistically significant differences in cerebellar GM and CSF volumes between patients and controls were found. Moreover, a significant difference was not found between the WM volumes. This may suggest that there are changes in structural complexity in WM even when its volume is unaffected. We conclude that the findings of this preliminary study indicate the possibility of using FD analysis to understand the pathophysiology of CM-I in patients.

Comparison of posterior fossa volumes and clinical outcomes after decompression of Chiari malformation Type I

OBJECTIVE Previous studies have indicated an association of Chiari malformation Type I (CM-I) and a small posterior fossa. Most of these studies have been limited by 2D quantitative methods, and more recent studies utilizing 3D methodologies are time-intensive with manual segmentation. The authors sought to develop a more automated tool to calculate the 3D posterior fossa volume, and correlate its changes after decompression with surgical outcomes. METHODS A semiautomated segmentation program was developed, and used to compare the pre- and postoperative volumes of the posterior cranial fossa (PCF) and the CSF spaces (cisterna magna, prepontine cistern, and fourth ventricle) in a cohort of pediatric patients with CM-I. Volume changes were correlated with postoperative symptomatic improvements in headache, syrinx, tonsillar descent, cervicomedullary kinking, and overall surgical success. RESULTS Forty-two pediatric patients were included in this study. The mean percentage increase in PCF volume was significantly greater in patients who showed clinical improvement versus no improvement in headache (5.89% vs 1.54%, p < 0.05) and tonsillar descent (6.52% vs 2.57%, p < 0.05). Overall clinical success was associated with a larger postoperative PCF volume increase (p < 0.05). These clinical improvements were also significantly associated with a larger increase in the volume of the cisterna magna (p < 0.05). The increase in the caudal portion of the posterior fossa volume was also larger in patients who showed improvement in syrinx (6.63% vs 2.58%, p < 0.05) and cervicomedullary kinking (9.24% vs 3.79%, p < 0.05). CONCLUSIONS A greater increase in the postoperative PCF volume, and specifically an increase in the cisterna magna volume, was associated with a greater likelihood of clinical improvements in headache and tonsillar descent in patients with CM-I. Larger increases in the caudal portion of the posterior fossa volume were also associated with a greater likelihood of improvement in syrinx and cervicomedullary kinking.

The suboccipital ligament

OBJECTIVE A fibrous structure located dorsal to the dura at the posterior craniocervical junction stretches horizontally between the bilateral occipital condyles and the upper borders of the C-1 laminae. Partially covered by the occipital bone, this structure is always encountered when the bone is removed from the foramen magnum rim during approaches to the posterior cranial fossa. Although known to surgeons, this structure has not been defined, studied, or named. The most appropriate name for this structure is "the suboccipital ligament," and a detailed rationale for this name is provided. METHODS This 3-year-long study included 10 cadaveric specimens and 39 clinical patients: 31 consecutive surgically treated patients with Chiari Type I malformations (CM-I subgroup) and 8 other patients with posterior fossa pathologies (non-CM-I subgroup). The dimensions were defined, the function of this ligament was hypothesized, size and histological composition were compared between patient subgroups, and its origin and relationship to the surrounding structures were analyzed. Possible statistical differences in the parameters between the 2 groups were also evaluated. RESULTS The suboccipital ligament consists of horizontally oriented hyaline fibers and has a median length of 35 mm, height of 10 mm, and thickness of 0.5 mm. These dimensions are not significantly different between the CM-I and non-CM-I patients. The median age of the patients was 43 years, with CM-I patients being significantly younger (median 35 years) than non-CM-I patients (median 57 years). There was no statistically significant difference in weight, height, and body mass index between patient subgroups. There was no significant correlation between the body mass index or height of the patients and the dimensions of the ligament. No statistically significant differences existed between the subgroups in terms of smoking history, alcohol consumption, and the presence of diabetes mellitus, hypertension, hydrocephalus, or headaches. The ligament tissue in the CM-I patients was disorganized with poorly arranged collagen bands and interspersed adipose tissue. These patients also had more hyalinized fibrosis and showed changes in the direction of fibers, with hyaline nodules ranging from 0 to 2+. The result of the histological evaluation of the suboccipital ligament for hyaline nodules, calcification, and ossification was graded as 2+ if present in 3 or more medium-power magnification fields (MPFs); 1+ if present in 1-2 MPFs; and 0, if present in less than 1 MPF. Histological examination of the ligaments showed structural differences between CM-I and non-CM-I patients, most notably the presence of hyaline nodules and an altered fiber orientation in CM-I patients. CONCLUSIONS The suboccipital ligament extends between the occipital condyle and the superior edge of the C-1 lamina, connecting the contralateral sides, and appears to function as a real ligament. It is ventral to the occipital bone, which covers approximately two-thirds of the height of the ligament and is loosely attached to the dura medially and more firmly laterally. Because of its distinctive anatomy, characteristics, and function, the suboccipital ligament deserves its own uniform designation and name.

[Treatment of syringomyelia associated with Chiari 1 malformation]

Syringomyelia (SM) develops due to the disturbance of cerebrospinal fluid dynamics, spinal fixation or a spinal tumor. The disturbance of cerebrospinal fluid dynamics in the area of the foramen magnum leads to the progression of SM in Chiari 1 malformation (CM1). CM1 is the most prevalent pathology of craniovertebral junction associated with SM. The prevalence of CM1 varies from 3 to 8 per 100 000 population but SM is diagnosed in 65% of patients with CM1. Clinical symptoms of CM1 and SM include pain in the occipital area, gait disturbances due to sensitive ataxia, dissociated sensory disorders, dysphagia, paresis of the extremities. In most patients, symptoms of SM progressed over the years. The diagnosis is based on MRI results of the brain and spinal cord. Phase-contrast MRI is used to study the disturbance of cerebrospinal fluid dynamics in details. Progression of SM or CM1 symptoms needs surgical treatment - decompression of the posterior cranial fossa for the recovery of normal cerebrospinal fluid dynamics.

Computed tomographic study of posterior cranial fossa, foramen magnum, and its surgical implications in Chiari malformations

Objective:

The aim of this study is to measure the height and volume of the bony part of the posterior cranial fossa (PCF) and the surface area of the foramen magnum (FM) using computed tomography (CT) scans and to correlate our clinical findings with the available current literature.

Materials and Methods:

This cross-sectional study was conducted in a tertiary care referral hospital in the Southern part of India during the period from January 2015 to August 2015. A total of 100 CT scans of the suspected head injury patients were collected retrospectively form the basis for this study. The height, volume of PCF and the anteroposterior (AP), transverse diameter, and surface area of the FM were measured. The values of all parameters were subjected to statistical analysis using SPSS version 16.

Results:

The age of the patients were ranged between 18 and 70 years with the mean age of 41.22 ± 13.93 years. The dimensions of the posterior fossa and FM were larger in males compared to females. The mean height of the posterior fossa was 38.08 (±4.718) mm (P = 0.0001), and the mean volume of the posterior fossa was 157.23 (±6.700) mm³ (P = 0.0001). The mean AP, transverse diameter, and the surface area of the FM were 33.13 (± 3.286) mm, 29.01 (± 3.081) mm, and 763.803 (±138.276) mm², respectively.

Conclusion:

The normal dimensions of the posterior fossa and FM were less in females than males and were useful to radiologists and neurosurgeons to better their diagnostic inferences, as well as to determine the proper treatment options in Chiari malformation type I (CMI) and other posterior fossa anomalies. The posterior fossa tissue volume can be reliably measured in patients with CMI using our method. More studies were required because there were variations in dimensions among individuals of different races in different regions of the world.

Contemporary occurrence of hydrocephalus and Chiari I malformation in sagittal craniosynostosis. Case report and review of the literature

Chiari malformation type I (CM-I) and hydrocephalus are often associated with complex craniosynostosis. On the contrary, their simultaneous occurrence in monosutural synostosis is extremely rare. The pathophysiological hypothesis is that they may alter posterior fossa growth and lead to cerebellar tonsil herniation also without skull base primary involvement. Hydrocephalus is multifactorial and may be secondary to fourth ventricle outlet obstruction. The management of these cases is quite complex and not well defined. Cranial vault remodeling should be the only treatment when CM-I is asymptomatic and not related to syringomyelia. Suboccipital decompression should be reserved only in complicated CM-I, usually as a second surgical step following the correction of the supratentorial deformity. In our opinion, the associated hydrocephalus should be treated first in order to normalize intracranial hypertension before opening the cranial sutures. We report the case of a 26-month-old child that presented with sagittal craniosynostosis, hydrocephalus, and CM-I. He was managed by performing endoscopic third ventriculostomy (ETV) first and cranial vault remodeling thereafter. Clinico-radiological outcome was very satisfying. Concerning literature is reviewed; physiopathology and surgical management are discussed.

"Stealth cranioplasty:" A novel endeavor for symptomatic adult Chiari I patients with syringomyelia: Technical note, appraisal, and philosophical considerations

Aim and Objective:

In this article, we describe a novel technique of reconstruction of posterior fossa by cranioplasty with use of preshaped titanium mesh following posterior fossa decompression (PFD) for Chiari malformation type I (CMI) with syringomyelia (SM) in symptomatic adults.

Materials and Methods:

Eleven patients underwent limited PFD and expansive cranioplasty with preshaped titanium mesh, what we term as “Stealth Cranioplasty” (SCP), following arachnoid preserving duraplasty (APD) and hexagonal tenting of the duraplasty with the cranioplasty (HTDC) for the management of symptomatic adult CMI with SM. All these patients had syringes extending from 3 to >10 vertebral levels.

Results:

Seven male and four female symptomatic CMI adult patients, between age ranges of 22 and 44 years (mean 29.45 years), presented with different neurological symptoms related to CMI and SM for 6–84 months (mean 37.09 months). All the patients underwent PFD, APD followed by SCP and HTDC and were followed up for 7–54 months (mean 35.90 months). Of 11 patients, 8 patients improved according to the Chicago Chiari Outcome Scale (CCOS) with score of 13–15 while 3 patients remained unchanged with CCOS of 12, and there was no worsening. There was no complication related to Chiari surgery in any of the patients. All the patients had good reestablishment of cisterna magna. Two patients had marked reduction of syrinx while eight patients had moderate-to-mild reduction and one patient had no change of syrinx. None of the patients needed redo surgery.

Conclusion:

SCP is an effective, fruitful, and cost-effective technique for the management of symptomatic adult CMI with SM. This technique has the advantages of preventing complications and recurrences in addition to the improvement of symptoms by addressing the basic pathology.

Simultaneous total intracranial volume and posterior fossa volume estimation using multi-atlas label fusion

Total intracranial volume (TICV) is an essential covariate in brain volumetric analyses. The prevalent brain imaging software packages provide automatic TICV estimates. FreeSurfer and FSL estimate TICV using a scaling factor while SPM12 accumulates probabilities of brain tissues. None of the three provide explicit skull/CSF boundary (SCB) since it is challenging to distinguish these dark structures in a T1-weighted image. However, explicit SCB not only leads to a natural way of obtaining TICV (i.e., counting voxels inside the skull) but also allows sub-definition of TICV, for example, the posterior fossa volume (PFV). In this article, they proposed to use multi-atlas label fusion to obtain TICV and PFV simultaneously. The main contributions are: (1) TICV and PFV are simultaneously obtained with explicit SCB from a single T1-weighted image. (2) TICV and PFV labels are added to the widely used BrainCOLOR atlases. (3) Detailed mathematical derivation of non-local spatial STAPLE (NLSS) label fusion is presented. As the skull is clearly distinguished in CT images, we use a semi-manual procedure to obtain atlases with TICV and PFV labels using 20 subjects who both have a MR and CT scan. The proposed method provides simultaneous TICV and PFV estimation while achieving more accurate TICV estimation compared with FreeSurfer, FSL, SPM12, and the previously proposed STAPLE based approach. The newly developed TICV and PFV labels for the OASIS BrainCOLOR atlases provide acceptable performance, which enables simultaneous TICV and PFV estimation during whole brain segmentation. The NLSS method and the new atlases have been made freely available. Hum Brain Mapp 38:599-616, 2017. © 2016 Wiley Periodicals, Inc.

Two distinct populations of Chiari I malformation based on presence or absence of posterior fossa crowdedness on magnetic resonance imaging

OBJECTIVE A subset of patients with Chiari I malformation demonstrate patent subarachnoid spaces around the cerebellum, indicating that reduced posterior fossa volume alone does not account for tonsillar descent. The authors distinguish two subsets of Chiari I malformation patients based on the degree of "posterior fossa crowdedness" on MRI. METHODS Two of the coauthors independently reviewed the preoperative MR images of 49 patients with Chiari I malformation and categorized the posterior fossa as "spacious" or "crowded." Volumetric analysis of posterior fossa structures was then performed using open-source DICOM software. The preoperative clinical and imaging features of the two groups were compared. RESULTS The posterior fossae of 25 patients were classified as spacious and 20 as crowded by both readers; 4 were incongruent. The volumes of the posterior fossa compartment, posterior fossa tissue, and hindbrain (posterior fossa tissue including herniated tonsils) were statistically similar between the patients with spacious and crowed subtypes (p = 0.33, p = 0.17, p = 0.20, respectively). However, patients in the spacious and crowded subtypes demonstrated significant differences in the ratios of posterior fossa tissue to compartment volumes as well as hindbrain to compartment volumes (p = 0.001 and p = 0.0004, respectively). The average age at surgery was 29.2 ± 19.3 years (mean ± SD) and 21.9 ± 14.9 years for spacious and crowded subtypes, respectively (p = 0.08). Syringomyelia was more prevalent in the crowded subtype (50% vs 28%, p = 0.11). CONCLUSIONS The authors' study identifies two subtypes of Chiari I malformation, crowded and spacious, that can be distinguished by MRI appearance without volumetric analysis. Earlier age at surgery and presence of syringomyelia are more common in the crowded subtype. The presence of the spacious subtype suggests that crowdedness alone cannot explain the pathogenesis of Chiari I malformation in many patients, supporting the need for further investigation.

Magnetic resonance imaging-based measures predictive of short-term surgical outcome in patients with Chiari malformation Type I: a pilot study

OBJECTIVE This study identifies quantitative imaging-based measures in patients with Chiari malformation Type I (CM-I) that are associated with positive outcomes after suboccipital decompression with duraplasty. METHODS Fifteen patients in whom CM-I was newly diagnosed underwent MRI preoperatively and 3 months postoperatively. More than 20 previously described morphological and physiological parameters were derived to assess quantitatively the impact of surgery. Postsurgical clinical outcomes were assessed in 2 ways, based on resolution of the patient's chief complaint and using a modified Chicago Chiari Outcome Scale (CCOS). Statistical analyses were performed to identify measures that were different between the unfavorable- and favorable-outcome cohorts. Multivariate analysis was used to identify the strongest predictors of outcome. RESULTS The strongest physiological parameter predictive of outcome was the preoperative maximal cord displacement in the upper cervical region during the cardiac cycle, which was significantly larger in the favorable-outcome subcohorts for both outcome types (p < 0.05). Several hydrodynamic measures revealed significantly larger preoperative-to-postoperative changes in the favorable-outcome subcohort. Predictor sets for the chief-complaint classification included the cord displacement, percent venous drainage through the jugular veins, and normalized cerebral blood flow with 93.3% accuracy. Maximal cord displacement combined with intracranial volume change predicted outcome based on the modified CCOS classification with similar accuracy. CONCLUSIONS Tested physiological measures were stronger predictors of outcome than the morphological measures in patients with CM-I. Maximal cord displacement and intracranial volume change during the cardiac cycle together with a measure that reflects the cerebral venous drainage pathway emerged as likely predictors of decompression outcome in patients with CM-I.

Primary Cough Headache is Associated with Posterior Fossa Crowdedness: A Morphometric MRI Study

The aetiology of primary cough headache (PCH) is obscure. The aim of this study was to investigate the magnetic resonance (MR) morphometric characteristics of the posterior cranial fossa (PCF) in patients with PCH. Eighteen consecutive patients with PCH (14M/4F, mean age 75.1 + 6.0 years) and 18 sex- and age-matched control subjects were recruited for study. Based on the midline sagittal MR images, parameters indicating posterior fossa crowdedness were measured. Compared with controls, patients with PCH had a similar size of hindbrain tissue area but a significantly smaller PCF area, resulting in a higher mean hindbrain/PCF ratio (0.78 + 0.04 vs. 0.73 + 0.06, P = 0.005). In addition, these patients also had a lower position of the cerebellar tonsillar tip, a shorter clivus length and shorter distances from the clivus to the mid-pons and from the basion to the medulla than the control group. Patients with PCH were associated with a more crowded PCF, which might be a contributing factor for the pathogenesis of this headache syndrome.

Acute Foramen Magnum Syndrome Following Single Diagnostic Lumbar Puncture: Consequence of a Small Posterior Fossa?

BACKGROUND

Type I Chiari malformation (CMI) is a rare complication of lumbar cerebrospinal fluid (CSF) drainage that is usually reported after lumbar drain or lumboperitoneal shunt placement. It usually remains asymptomatic; however, even if it becomes symptomatic, symptoms are usually mild. There are only a few reports of acute foramen magnum syndrome following continuous lumbar CSF drainage, and acute foramen magnum syndrome after a single diagnostic lumbar puncture (LP) has not been previously reported. We encountered this catastrophic complication in one of our patient.

CASE DESCRIPTION

A 30-year-old woman with a large supratentorial meningioma and associated asymptomatic CMI presented with holocranial headache. She underwent successful and uneventful excision of the tumor. However, she developed quadriplegia and respiratory arrest 48 hours following a diagnostic LP performed on postoperative day 9. She underwent urgent posterior fossa decompression after magnetic resonance imaging showed increased tonsillar impaction and swelling along with cervicomedullary compression. Postoperatively, she steadily improved and regained normal power after 3 months. Retrospective quantitative analysis of magnetic resonance imaging (MRI) revealed a small posterior fossa.

CONCLUSIONS

The association of intracranial tumors and lumbar CSF drainage with CMI is uncommon. The documentation of a small posterior fossa signifies the importance of both developmental (small posterior fossa) and acquired (intracranial tumor/lumbar CSF drainage) factors in pathogenesis of CMI. Although the extreme rarity of acute deterioration following a single LP does not warrant LP to be contraindicated in such patients, documentation of resolution of CMI with postoperative MRI before performing lumbar CSF drainage (whether therapeutic or diagnostic), might be helpful in avoiding this rare complication.

Morphometric Analysis of Predictors of Cervical Syrinx Formation in the Setting of Chiari I Malformation

BACKGROUND/AIMS

We performed a morphometric analysis of Chiari I malformations to look for predictors of cervical syrinx formation.

METHODS

Eighteen patients with Chiari I malformation and associated cervical syrinx and 16 patients with Chiari I malformation without associated cervical syrinx were included in the study. Chiari I size was obtained from the radiology report; foramen magnum diameter, cerebellar volume, posterior fossa volume and intracranial volume were calculated using OsiriX software, and average measurements were compared between the two groups.

RESULTS AND CONCLUSION

Patients with Chiari I with syrinx had an average tonsillar descent of 13.03 ± 5.31 mm compared to 9.25 ± 3.31 mm in the Chiari I without syrinx group (p < 0.05). Patients with Chiari I and syrinx also showed increased cerebellar crowding with a higher cerebellar volume to posterior fossa volume ratio; however, this difference was not significant (0.83 vs. 0.81; p = 0.1872). No difference between groups was found in posterior fossa volume, intracranial volume and foramen magnum diameter. Therefore, only Chiari I size based on the extent of tonsillar herniation was found to be a determinant of cervical syrinx formation.

Cerebellar and hindbrain motion in Chiari malformation with and without syringomyelia

OBJECTIVE

The pathogenesis of syringomyelia associated with Chiari malformation type I (CM-I) is unclear. Theories of pathogenesis suggest the cerebellar tonsils may obstruct CSF flow or alter pressure gradients, or their motion might act as a piston to increase CSF pressure in the spinal subarachnoid space. This study was performed to measure cerebellar tonsillar and hindbrain motion in CM-I and assess the potential contributions to syrinx formation.

METHODS

Sixty-four CM-I patients and 25 controls were retrospectively selected from a clinical database, and all subjects had undergone cardiac-gated cine balanced fast-field echo MRI. There were a total of 36 preoperative CM-I scans, which consisted of 15 patients with and 21 patients without syringomyelia. Nineteen patients underwent paired pre- and postoperative imaging. Anteroposterior (AP) and superoinferior (SI) movements of the tip of the cerebellar tonsils, obex, fastigium of the fourth ventricle, pontomedullary junction, and cervicomedullary junction were measured. The distance between the fastigium and tip of the tonsils was used to calculate tonsillar tissue strain (Δi/i0).

RESULTS

CM-I patients had significantly greater cerebellar tonsillar motion in both the AP and SI directions than controls (AP +0.34 mm [+136%], p < 0.001; SI +0.49 mm [+163%], p < 0.001). This motion decreased after posterior fossa decompression (AP -0.20 mm [-33%], p = 0.001; SI -0.29 mm [-36%]; p < 0.001), but remained elevated above control levels (AP +56%, p = 0.021; SI +67%, p = 0.015). Similar trends were seen for all other tracked landmarks. There were no significant differences in the magnitude or timing of motion throughout the hindbrain between CM-I patients with and without syringomyelia. Increased tonsillar tissue strain correlated with Valsalva headaches (p = 0.03).

CONCLUSIONS

Cerebellar tonsillar motion may be a potential marker of CM-I and may have use in tailoring surgical procedures. The lack of association with syringomyelia suggests that tonsillar motion alone is not the driver of syrinx formation. Tonsillar tissue strain may play a part in the pathophysiology of Valsalva headaches.

Stereological and Morphometric Analysis of MRI Chiari Malformation Type-1

Objective

In this study, we aimed to investigate the underlying ethiological factors in chiari malformation (CM) type-I (CMI) via performing volumetric and morphometric length-angle measurements.

Methods

A total of 66 individuals [33 patients (20-65 years) with CMI and 33 control subjects] were included in this study. In sagittal MR images, tonsillar herniation length and concurrent anomalies were evaluated. Supratentorial, infratentorial, and total intracranial volumes were measured using Cavalieri method. Various cranial distances and angles were used to evaluate the platybasia and posterior cranial fossa (PCF) development.

Results

Tonsillar herniation length was measured 9.09±3.39 mm below foramen magnum in CM group. Tonsillar herniation/concurrent syringomyelia, concavity/defect of clivus, herniation of bulbus and fourth ventricle, basilar invagination and craniovertebral junction abnormality rates were 30.3, 27, 18, 2, 3, and 3 percent, respectively. Absence of cisterna magna was encountered in 87.9% of the patients. Total, IT and ST volumes and distance between Chamberlain line and tip of dens axis, Klaus index, clivus length, distance between internal occipital protuberance and opisthion were significantly decreased in patient group. Also in patient group, it was found that Welcher basal angle/Boogard angle increased and tentorial slope angle decreased.

Conclusion

Mean cranial volume and length-angle measurement values significantly decreased and there was a congenital abnormality association in nearly 81.5 percent of the CM cases. As a result, it was concluded that CM ethiology can be attributed to multifactorial causes. Moreover, congenital defects can also give rise to this condition.

Comparison of clinical and radiological manifestations and surgical outcomes of pediatric Chiari I malformations in different age groups

PURPOSE

The aim of this study was to elucidate the differences in clinical and radiological manifestations and treatment outcomes of pediatric Chiari I malformation patients according to age.

METHODS

We retrospectively reviewed the patients who received surgery in our institution for symptomatic Chiari I malformations between January 1991 and December 2012. Fifty-four patients were identified, and their medical records were reviewed for clinical presentation, radiological findings, surgical treatment, and outcomes including complications. We divided the patients into 3 groups: Group I (n = 4) younger than 3 years old; Group II (n = 9) between 3 and 5 years old; and Group III (n = 41) older than 5 years old. Surveyed data were compared among the groups. The mean follow-up period was 82.8 months.

RESULTS

All of Group I patients presented with stem compression signs. Ventriculomegaly was common (3/4, 75%), but no syrinx or scoliosis was observed. In Group II, scoliosis was the most common presentation (5/9, 56%), and these patients rarely complained any other symptoms. Pain, such as headache (18/41, 44%), was the predominant presentation in Group III. The incidences of syrinx and scoliosis were similar in Groups II and III. There were no differences in the treatment outcomes among the groups. The spinal curve did not improve in 4 of 5 Group II patients despite their early FMD surgeries. The incidence of complications related to cerebrospinal fluid leakage was higher in the young age group.

CONCLUSIONS

The clinical and radiological manifestations of pediatric Chiari I malformation appeared to be different according to age.

Surgical History of Sleep Apnea in Pediatric Patients with Chiari Type 1 Malformation

Sleep apnea represents a relative indication for posterior fossa decompression in pediatric patients with Chiari malformation type 1. Duraplasty was associated with improvement of sleep apnea in 100% of patients and dural splitting with improvement in 50% of patients. Duraplasty and dural splitting were associated with a similar reduction in tonsillar herniation on radiographic imaging of 58% (37% excluding tonsillectomy) and 35%, respectively. Longitudinal follow-up studies of patients with either neurologic deficits or severe symptoms will further elucidate the natural history of Chiari malformation type 1 and more appropriately gauge the risk-benefit tradeoff of surgical intervention.

Fractal dimension analysis of cerebellum in Chiari Malformation type I

Chiari Malformation type I (CM-I) is a serious neurological disorder that is characterized by hindbrain herniation. Our aim was to evaluate the usefulness of fractal analysis in CM-I patients. To examine the morphological complexity features of this disorder, fractal dimension (FD) of cerebellar regions were estimated from magnetic resonance images (MRI) of 17 patients with CM-I and 16 healthy control subjects in this study. The areas of white matter (WM), gray matter (GM) and cerebrospinal fluid (CSF) were calculated and the corresponding FD values were computed using a 2D box-counting method in both groups. The results indicated that CM-I patients had significantly higher (p<0.05) FD values of GM, WM and CSF tissues compared to control group. According to the results of correlation analysis between FD values and the corresponding area values, FD and area values of GM tissues in the patients group were found to be correlated. The results of the present study suggest that FD values of cerebellar regions may be a discriminative feature and a useful marker for investigation of abnormalities in the cerebellum of CM-I patients. Further studies to explore the changes in cerebellar regions with the help of 3D FD analysis and volumetric calculations should be performed as a future work.

Magnetic resonance imaging measures of posterior cranial fossa morphology and cerebrospinal fluid physiology in Chiari malformation type I

BACKGROUND

It has been well documented that, along with tonsillar herniation, Chiari Malformation Type I (CMI) is associated with smaller posterior cranial fossa (PCF) and altered cerebrospinal fluid (CSF) flow and tissue motion in the craniocervical junction.

OBJECTIVE

This study assesses the relationship between PCF volumetry and CSF and tissue dynamics toward a combined imaging-based morphological-physiological characterization of CMI. Multivariate analysis is used to identify the subset of parameters that best discriminates CMI from a healthy cohort.

METHODS

Eleven length and volumetric measures of PCF, including crowdedness and 4th ventricle volume, 4 measures of CSF and cord motion in the craniocervical junction, and 5 global intracranial measures, including intracranial compliance and pressure, were measured by magnetic resonance imaging (MRI) in 36 symptomatic CMI subjects (28 female, 37 ± 11 years) and 37 control subjects (24 female, 36 ± 12 years). The CMI group was further divided based on symptomatology into "typical" and "atypical" subgroups.

RESULTS

Ten of the 20 morphologic and physiologic measures were significantly different between the CMI and the control cohorts. These parameters also had less variability and stronger significance in the typical CMI compared with the atypical. The measures with the most significance were clival and supraocciput lengths, PCF crowdedness, normalized PCF volume, 4th ventricle volume, maximal cord displacement (P < .001), and MR measure of intracranial pressure (P = .007). Multivariate testing identified cord displacement, PCF crowdedness, and normalized PCF as the strongest discriminator subset between CMI and controls. MR measure of intracranial pressure was higher in the typical CMI cohort compared with the atypical.

CONCLUSION

The identified 10 complementing morphological and physiological measures provide a more complete and symptomatology-relevant characterization of CMI than tonsillar herniation alone.

Demographic confounders in volumetric MRI analysis: is the posterior fossa really small in the adult Chiari 1 malformation?

OBJECTIVE

Measurement of posterior fossa volume has been proposed to have diagnostic utility and physiologic significance in the Chiari malformation type 1. This study evaluated the effects of demographics on posterior fossa volume and total intracranial volume in adult control subjects, adult patients with Chiari malformation type 1, and adult patients with idiopathic intracranial hypertension, who may share some imaging features of patients with Chiari malformation type 1.

MATERIALS AND METHODS

Twenty-eight patients with Chiari malformation type 1, 21 patients with idiopathic intracranial hypertension, and 113 control subjects underwent brain MRI including contrast-enhanced 3D gradient-recalled echo (GRE) T1-weighted imaging. Linear measurements of the posterior fossa and intracranial space were obtained. Manual segmentation of the posterior fossa and intracranial space was performed to yield posterior fossa volume and total intracranial volume. Age, sex, race, and body mass index (weight in kilograms divided by the square of height in meters; BMI) were controlled for when comparing cohorts.

RESULTS

Three of the 12 linear measurements significantly predicted total intracranial volume (accounting for 74% of variance), and four predicted posterior fossa volume (54% of variance). Age, race, sex, and BMI each statistically significantly influenced posterior fossa volume and total intracranial volume. No statistically significant differences in posterior fossa volume, total intracranial volume, or ratio of posterior fossa volume to total intracranial volume were seen between the Chiari malformation type 1 group and control group after controlling for demographics. Patients with idiopathic intracranial hypertension were more likely than control subjects to have smaller posterior fossa volumes (odds ratio [OR]=1.81; p=0.01) and larger total intracranial volumes (OR=1.24; p=0.06).

CONCLUSION

Linear measurements of the posterior fossa are not strong predictors of posterior fossa volume. Age, race, sex, and BMI have statistically significant effects on intracranial measurements that must be considered, particularly with respect to posterior fossa volume in Chiari malformation type 1. Even when these demographic variables are appropriately accounted for, other similarly presenting diseases may show small posterior fossa volumes.

Impact of body mass index on cerebellar tonsil position in healthy subjects and patients with Chiari malformation

OBJECT

It is unclear if there is a relationship between Chiari malformation Type I (CM-I) and body mass index (BMI). The aim of this study was to identify the relationship between BMI and cerebellar tonsil position in a random sample of people.

METHODS

Cerebellar tonsil position in 2400 subjects from a cohort of patients undergoing MRI was measured. Three hundred patients were randomly selected from each of 8 age groups (from 0 to 80 years). A subject was then excluded if he or she had a posterior fossa mass or previous posterior fossa decompression or if height and weight information within 1 year of MRI was not recorded in the electronic medical record.

RESULTS

There were 1310 subjects (54.6%) with BMI records from within 1 year of the measured scan. Of these subjects, 534 (40.8%) were male and 776 (59.2%) were female. The average BMI of the group was 26.4 kg/m(2), and the average tonsil position was 0.87 mm above the level of the foramen magnum. There were 46 subjects (3.5%) with a tonsil position ≥ 5 mm below the level of the foramen magnum. In the group as a whole, there was no correlation (R(2) = 0.004) between BMI and cerebellar tonsil position.

CONCLUSIONS

In this examination of 1310 subjects undergoing MRI for any reason, there was no relationship between BMI and the level of the cerebellar tonsils or the diagnosis of CM-I on imaging.

Incidental findings on brain and spine imaging in children

In recent years, the utilization of diagnostic imaging of the brain and spine in children has increased dramatically, leading to a corresponding increase in the detection of incidental findings of the central nervous system. Patients with unexpected findings on imaging are often referred for subspecialty evaluation. Even with rational use of diagnostic imaging and subspecialty consultation, the diagnostic process will always generate unexpected findings that must be explained and managed. Familiarity with the most common findings that are discovered incidentally on diagnostic imaging of the brain and spine will assist the pediatrician in providing counseling to families and in making recommendations in conjunction with a neurosurgeon, when needed, regarding additional treatments and prognosis.

Pediatric and adult Chiari malformation Type I surgical series 1965-2013: a review of demographics, operative treatment, and outcomes

OBJECT

Chiari malformation Type I (CM-I) is a hindbrain disorder associated with elongation of the cerebellar tonsils, which descend below the foramen magnum into the spinal canal. It occurs in children and adults. Clinical symptoms mainly develop from alterations in CSF flow at the foramen magnum and the common subsequent development of syringomyelia.

METHODS

The authors reviewed English-language reports of pediatric, adult, and combined (adult and pediatric) surgical series of patients with CM-I published from 1965 through August 31, 2013, to investigate the following: 1) geographical distribution of reports; 2) demographics of patients; 3) follow-up lengths; 4) study durations; 5) spectrum and frequency of surgical techniques; 6) outcomes for neurological status, syrinx, and headache; 7) frequency and scope of complications; 8) mortality rates; and 9) differences between pediatric and adult populations. Research and inclusion criteria were defined, and all series that contained at least 4 cases and all publications with sufficient data for analysis were included.

RESULTS

The authors identified 145 operative series of patients with CM-I, primarily from the United States and Europe, and divided patient ages into 1 of 3 categories: adult (>18 years of age; 27% of the cases), pediatric (≤18 years of age; 30%), or unknown (43%). Most series (76%) were published in the previous 21 years. The median number of patients in the series was 31. The mean duration of the studies was 10 years, and the mean follow-up time was 43 months. The peak ages of presentation in the pediatric studies were 8 years, followed by 9 years, and in the adult series, 41 years, followed by 46 years. The incidence of syringomyelia was 65%. Most of the studies (99%) reported the use of posterior fossa/foramen magnum decompression. In 92%, the dura was opened, and in 65% of these cases, the arachnoid was opened and dissected; tonsillar resection was performed in 27% of these patients. Postoperatively, syringomyelia improved or resolved in 78% of the patients. Most series (80%) reported postoperative neurological outcomes as follows: 75% improved, 17% showed no change, and 9% experienced worsening. Postoperative headaches improved or resolved in 81% of the patients, with a statistical difference in favor of the pediatric series. Postoperative complications were reported for 41% of the series, most commonly with CSF leak, pseudomeningocele, aseptic meningitis, wound infection, meningitis, and neurological deficit, with a mean complication rate of 4.5%. Complications were reported for 37% of pediatric, 20% of adult, and 43% of combined series. Mortality was reported for 11% of the series. No difference in mortality rates was seen between the pediatric and adult series.

CONCLUSIONS

Before undergoing surgical treatment for CM-I, symptomatic patients and their families should be given clear information about the success of treatment and potential complications. Furthermore, surgeons may benefit from comparing published data with their own. In the future, operative CM-I reports should provide all details of each case for the purpose of comparison.

Upward Translation of Cerebellar Tonsils following Surgical Expansion of Supratentorial Cranial Vault: A Unified Biomechanical Explanation of Chiari Type I

Cerebellar tonsils moved significantly upward in 3 patients with Chiari type I who underwent supratentorial cranial vault expansion to alleviate intracranial pressure related to multisutural craniosynostosis. The Chiari type I deformities in these patients were the biomechanical consequence of posterior fossa-cerebellar disproportion caused by supratentorial craniocerebral disproportion secondary to multisutural craniosynostosis. The authors postulate that all cases of Chiari type I deformity share the sine qua non feature of posterior fossa-cerebellar disproportion.

Factors contributing to improvement of syringomyelia after foramen magnum decompression for Chiari type I malformation

BACKGROUND

Although various surgical approaches have been proposed for treating syringomyelia associated with Chiari type I malformation, a standard method has yet to be established. we prospectively investigated the results of our surgical method: foramen magnum decompression combined with C1 laminectomy and excision of the outer layer of the dura mater.

METHODS

Twenty patients underwent surgery between 2000 and 2010 at our hospital. After surgery, the size of the syrinx decreased in 11 patients (decreased group) but remained unchanged in nine patients (unchanged group). The following parameters were compared: age at the time of surgery, duration of morbidity, improvement of preoperative symptoms, morphological type and length of the syrinx, presence or absence of scoliosis, cervical alignment, basal and clivo-axial angles, and postoperative subarachnoid space at the foramen magnum level.

RESULTS

Preoperative symptoms improved in all patients in the decreased group but in only one patient in the unchanged group. The average duration of morbidity was significantly shorter in the decreased group. Morphological examination revealed that the size of all central-type syrinxes decreased after surgery, whereas in all cases of deviated-type syrinx, size was unchanged. The average length of preoperative syrinx was significantly shorter in the decreased group. The postoperative subarachnoid space at the foramen magnum was enlarged in the entire decreased group, whereas residual narrowing of the space was observed in 44 % of patients in the unchanged group. No significant intergroup differences were observed in the other factors.

CONCLUSIONS

In patients with syringomyelia, a longer and deviated type of syrinx, a longer duration of morbidity, and postoperative residual narrowing of the subarachnoid space are associated with a poor prognosis after the surgical procedure. The pathogenesis of syringomyelia is inconsistent, and the choice of surgical technique for each pathological condition is important.

Association of increased body mass index with Chiari malformation Type I and syrinx formation in adults

Object

In this paper the authors describe an association between increased body mass index (BMI) and Chiari malformation Type I (CM-I) in adults, as well as its relationship to the development of syringomyelia.

Methods

In the period between January 2004 and December 2011, the senior author reviewed the data for all CM-I patients with or without syringomyelia and neurological deficit. Analyzed factors included clinical status (headaches and neurological signs), radiological characteristics of syringomyelia (diameter and vertical extent of syrinx), BMI, and relationship of age to BMI, syrinx diameter, and vertical extent of syrinx.

Results

Sixty consecutive adults had CM-I, 26 of whom also had syringomyelia. The mean BMI among all patients was 30.35 ± 7.65, which is Class I obesity (WHO), and was similar among patients with or without syringomyelia. Extension of the vertical syrinx was greater in overweight patients (p = 0.027) than in those with a normal body weight. Evidence of de novo syrinx formation was found in 2 patients who gained an average BMI of 10.8 points. After repeated decompression and no change in holocord syrinx width or vertical extent, a reduction in the syrinx was seen after BMI decreased 11.7 points in one individual. No correlation was found between patient age and BMI, age and vertical extension of the syrinx, and age and diameter of the syrinx.

Conclusions

An association between increased BMI and CM-I in adults was recognized. Gaining weight may influence the de novo creation of a syrinx in adults who previously had minimally symptomatic or asymptomatic CM-I, and reducing weight can improve a syrinx after unsuccessful surgical decompression. Therefore, a reduction in body weight should be recommended for all overweight and obese patients with CM-I.

"Triple R" tonsillar technique for the management of adult Chiari I malformation: surgical note

BACKGROUND

Chiari type I malformation is a congenital disorder that is characterized by the caudal extension of the cerebellar tonsils through the foramen magnum into the cervical canal and by a reduced posterior fossa volume.

METHODS

We report our surgical technique of reposition, reduction, or resection of the cerebellar tonsils for the management of Chiari I malformation. The procedure was performed in 22 adult patients, in three different centers, with a mean age of 37 years. Clinical complaints included headaches, nuchalgia, vertigo, and upper-limb weakness or numbness. Seven patients had cervical syringomyelia. Symptoms developed within a mean time of 36 months (range, 12-70 months).

RESULTS

The cerebellar tonsils were exposed through a dura mater-arachnoid incision at the atlanto-occipital space after a 0.5-cm rimming craniectomy of the occipital bone in all patients. In seven patients the tonsils were resected, in other seven were reduced by subpial coagulation and aspiration, and in the remaining eight patients the tonsils were repositioned after coagulating their surfaces. Three patients had also a posterior fossa arachnoid cyst that was fenestrated in two of them. All patients improved postoperatively. Syringomyelia was reduced in five of seven patients. The mean length of the follow-up period was 12 months.

CONCLUSIONS

Selective reposition, reduction, or resection of herniated cerebellar tonsils may improve symptoms in adult patients with Chiari I malformation.

Distribution of cerebellar tonsil position: implications for understanding Chiari malformation

OBJECT

Prior attempts to define normal cerebellar tonsil position have been limited by small numbers of patients precluding analysis of normal distribution by age group. The authors' objective in the present study was to analyze cerebellar tonsil location in every age range.

METHODS

Two thousand four hundred patients were randomly selected from a database of 62,533 consecutive patients undergoing MRI and were organized into 8 age groups. Magnetic resonance images were directly examined for tonsil location, morphology, and other features. Patients with a history or imaging findings of posterior fossa abnormalities unrelated to Chiari malformation (CM) were excluded from analysis. The caudal extent of the cerebellar tonsils was measured at the midsagittal and lowest parasagittal positions.

RESULTS

The mean tonsil height decreased slightly with advancing age into young adulthood and increased with advancing age in the adult age range. An increasing age in the adult age range was associated with a decreased likelihood of a tonsil position 5 mm or more below the foramen magnum (p = 0.0004). In general, the lowest tonsil position in each age group was normally distributed. Patients with pegged morphology were more likely to have a tonsil location at least 5 mm below the foramen magnum (85%), as compared with those having intermediate (38%) or rounded (2%) morphology (p < 0.0001). Female sex was associated with a lower mean tonsil position (p < 0.0001). Patients with a lower tonsil position also tended to have an asymmetrical tonsil position, usually lower on the right (p < 0.0001).

CONCLUSIONS

Cerebellar tonsil position follows an essentially normal distribution and varies significantly by age. This finding has implications for advancing our understanding of CM.

Automated posterior cranial fossa volumetry by MRI: applications to Chiari malformation type I

BACKGROUND AND PURPOSE

Quantification of PCF volume and the degree of PCF crowdedness were found beneficial for differential diagnosis of tonsillar herniation and prediction of surgical outcome in CMI. However, lack of automated methods limits the clinical use of PCF volumetry. An atlas-based method for automated PCF segmentation tailored for CMI is presented. The method performance is assessed in terms of accuracy and spatial overlap with manual segmentation. The degree of association between PCF volumes and the lengths of previously proposed linear landmarks is reported.

MATERIALS AND METHODS

T1-weighted volumetric MR imaging data with 1-mm isotropic resolution obtained with the use of a 3T scanner from 14 patients with CMI and 3 healthy subjects were used for the study. Manually delineated PCF from 9 patients was used to establish a CMI-specific reference for an atlas-based automated PCF parcellation approach. Agreement between manual and automated segmentation of 5 different CMI datasets was verified by means of the t test. Measurement reproducibility was established through the use of 2 repeated scans from 3 healthy subjects. Degree of linear association between PCF volume and 6 linear landmarks was determined by means of Pearson correlation.

RESULTS

PCF volumes measured by use of the automated method and with manual delineation were similar, 196.2 ± 8.7 mL versus 196.9 ± 11.0 mL, respectively. The mean relative difference of -0.3 ± 1.9% was not statistically significant. Low measurement variability, with a mean absolute percentage value of 0.6 ± 0.2%, was achieved. None of the PCF linear landmarks were significantly associated with PCF volume.

CONCLUSIONS

PCF and tissue content volumes can be reliably measured in patients with CMI by use of an atlas-based automated segmentation method.

Surgical treatment of Chiari malformation with and without syringomyelia: experience with 177 adult patients

Object

This study aims to show the relationship between clinical outcome in patients who underwent surgical decompression for Chiari malformation (CM) and postoperative imaging studies, with particular emphasis on the subarachnoid cisterns of the posterior fossa.

Methods

One hundred seventy-seven patients with CM, including 97 with syringomyelia, underwent posterior fossa decompressive surgery. Both the dura and arachnoid were opened in 150 of these patients, and 135 underwent reduction of the cerebellar tonsils. The patients' clinical signs and symptoms were evaluated at 2 time points after surgery. Their imaging studies were analyzed specifically for the size of the retrotonsillar and subtonsillar cisterns and the syringomyelic cavities. The authors evaluated the relationship between these imaging findings and clinical parameters.

Results

Clinical improvement correlated strongly with enlargement of the subarachnoid cisterns, and enlargement of the cisterns also correlated with reduction in size of the syrinx cavities. Symptoms related to syringomyelia responded to reduction in size of the syrinx cavities.

Conclusions

Surgical decompression of the posterior fossa should aim to create relatively large subarachnoid cisterns and reduce the size of the syrinx cavity. Reduction of the cerebellar tonsils by surgical means, together with duraplasty, achieves this goal and thereby improves the clinical outcome for patients with CM. An incidental observation of the study is that obesity increases the likelihood of headache in patients with CM.