Phenotypic definition of Chiari type I malformation coupled with high-density SNP genome screen shows significant evidence for linkage to regions on chromosomes 9 and 15

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.

Chiari I malformation: management evolution and technical innovation

BACKGROUND AND DEFINITION

In recent years thanks to the growing use of radiological assessment, Chiari I malformation became one of the major diseases for a neurosurgeon to deal with. CIM can be classified according to the extent of cerebellar tonsil tip into the foramen magnum being a protrusion over five mm considered pathological. Such a disease is a heterogeneous condition with a multifactorial pathogenetic mechanism that can subdivided into a primary and secondary form. Regardless of the form, it seems that CIM is the result of an imbalance between the volume of the braincase and its content. Acquired CIMs are secondary to conditions causing intracranial hypertension or hypotension while the pathogenesis of primary forms is still controversial.

PATHOGENESIS AND TREATMENT

There are several theories in the literature but the most accepted one implies an overcrowding due to a small posterior cranial fossa. While asymptomatic CIM do not need treatment, symptomatic ones prompt for surgical management. Several techniques are proposed being the dilemma centered in the need for dural opening procedures and bony decompression ones.

CONCLUSION

Alongside the paper, the authors will address the novelty presented in the literature on management, diagnosis and pathogenesis in order to offer a better understanding of such a heterogeneous pathology.

A likely HOXC4 predisposition variant for Chiari malformations

OBJECTIVE

Inherited variants predisposing patients to type 1 or 1.5 Chiari malformation (CM) have been hypothesized but have proven difficult to confirm. The authors used a unique high-risk pedigree population resource and approach to identify rare candidate variants that likely predispose individuals to CM and protein structure prediction tools to identify pathogenicity mechanisms.

METHODS

By using the Utah Population Database, the authors identified pedigrees with significantly increased numbers of members with CM diagnosis. From a separate DNA biorepository of 451 samples from CM patients and families, 32 CM patients belonging to 1 or more of 24 high-risk Chiari pedigrees were identified. Two high-risk pedigrees had 3 CM-affected relatives, and 22 pedigrees had 2 CM-affected relatives. To identify rare candidate predisposition gene variants, whole-exome sequence data from these 32 CM patients belonging to 24 CM-affected related pairs from high-risk pedigrees were analyzed. The I-TASSER package for protein structure prediction was used to predict the structures of both the wild-type and mutant proteins found here.

RESULTS

Sequence analysis of the 24 affected relative pairs identified 38 rare candidate Chiari predisposition gene variants that were shared by at least 1 CM-affected pair from a high-risk pedigree. The authors found a candidate variant in HOXC4 that was shared by 2 CM-affected patients in 2 independent pedigrees. All 4 of these CM cases, 2 in each pedigree, exhibited a specific craniocervical bony phenotype defined by a clivoaxial angle less than 125°. The protein structure prediction results suggested that the mutation considered here may reduce the binding affinity of HOXC4 to DNA.

CONCLUSIONS

Analysis of unique and powerful Utah genetic resources allowed identification of 38 strong candidate CM predisposition gene variants. These variants should be pursued in independent populations. One of the candidates, a rare HOXC4 variant, was identified in 2 high-risk CM pedigrees, with this variant possibly predisposing patients to a Chiari phenotype with craniocervical kyphosis.

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.

On the association between Chiari malformation type 1, bone mineral density and bone related genes

Background

Chiari malformation type 1 (C1M) is a neurological disease characterized by herniation of the cerebellar tonsils below the foramen magnum. Cranial bone constriction is suspected to be its main cause. To date, genes related to bone development (e.g. DKK1 or COL1A2) have been associated with C1M, while some bone diseases (e.g. Paget) have been found to cosegregate with C1M. Nevertheless, the association between bone mineral density (BMD) and C1M has not been investigated, yet. Here, we systematically investigate the association between C1M and BMD, and between bone related genes and C1M.

Methods

We have recruited a small cohort of C1M patients (12 unrelated patients) in whom we have performed targeted sequencing of an in-house bone-related gene panel and BMD determination through non-invasive DXA.

Results

In the search for association between the bone related genes and C1M we have found variants in more than one C1M patient in WNT16, CRTAP, MYO7A and NOTCH2. These genes have been either associated with craniofacial development in different ways, or previously associated with C1M (MYO7A). Regarding the potential link between BMD and C1M, we have found three osteoporotic patients and one patient who had high BMD, very close to the HBM phenotype values, although most patients had normal BMD.

Conclusions

Variants in bone related genes have been repeatedly found in some C1M cases. The relationship of bone genes with C1M deserves further study, to get a clearer estimate of their contribution to its etiology. No direct correlation between BMD and C1M was observed.

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We used an in-house bone gene panel to investigate a small cohort of C1M patients.

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Variants in WNT16, CRTAP, MYO7A and NOTCH2 were found in more than one C1M patient.

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No clear relationship was found between C1M and BMD in this small C1M cohort.

Are Two-Dimensional Morphometric Measures Reflective of Disease Severity in Adult Chiari I Malformation?

BACKGROUND

Two-dimensional (2D) morphometric measures have been previously used to diagnose Chiari I malformation (CMI) and distinguish patients from healthy subjects. There is, however, a paucity of literature regarding whether morphometric differences exist across the range of CMI disease severity. We evaluated whether 2D morphometrics demonstrate significant changes across standardized grades of CMI severity in adults.

METHODS

This retrospective observational study comprised 76 patients with symptomatic CMI with or without syringomyelia. Patients matched for age, sex, and body mass index were selected from each of the 3 severity grades of the Chiari Severity Index (CSI). The study used 17 2D craniocervical and posterior fossa morphometric variables that were previously found to differentiate patients with CMI from healthy subjects. The measurements were performed on midsagittal T1-weighted magnetic resonance imaging sequences using 2 custom in-house software tools, MorphPro and CerePro, and compared across CSI grades.

RESULTS

Analysis of variance showed that none of the 17 morphometric variables were significantly different across the 3 CSI grades (P > 0.003). Bayes factor 10 scores ranged from 0.11 to 0.82. Of variables, 9 had Bayes factor 10 scores between 0.10 and 0.30, while 8 had scores between 0.30 and 1. None of the Bayes factor 10 scores provided support for the alternative hypothesis that the morphometric measures differed across the CSI grades.

CONCLUSIONS

Our study indicated that 2D morphometrics are not reflective of CMI disease severity as indicated by the CSI grading system. The findings of our study support the need for further investigation into whether non-2D morphometric variables can be used as markers of disease severity.

[Clinical significance of subthreshold cerebellar tonsil ectopia into foramen magnum and Chiari malformation type 0]

Cerebellar tonsil dislocation into foramen magnum exceeding 5 mm is traditionally considered as Chiari malformation type 1. This disease requires surgical treatment in case of severe clinical manifestations. In patients with hypoplasia of posterior cranial fossa (PCF), subthreshold tonsil dislocations or tonsil position inside the foramen magnum can result clinical signs identical to Chiari malformation type 1. These disorders are presumably referred to phenotypic variant of Chiari malformation type 1 (Chiari malformation type 0). The authors discuss the data on the prevalence and mechanisms of cerebellar tonsil ectopia into foramen magnum, the role of hereditary and environmental factors in development of PCF hypoplasia and its role in Chiari malformation type 1 and 0. Significance of MR-based morphometry of PCF in identifying the primary forms (Chiari malformation type 1 and 0), clinical and radiological signs of malformation type 0, as well as data on surgical treatment of Chiari malformation type 0 combined and non-combined with syringomyelia are analyzed. Literature data confirm validity of the concept of Chiari malformation type 0. We emphasize the need for further analysis of this problem to identify sensitive and specific diagnostic signs of Chiari malformation type 0 and determine optimal treatment strategy.

Development of Progressive Chiari I Malformation in a Child with Unilateral Sporadic Retinoblastoma

Purpose:

To report a case of progressive Chiari malformation type I (CIM) in a patient with unilateral sporadic retinoblastoma (RB) treated with intra-arterial chemotherapy (IAC) and enucleation.

Methods:

A 5-year-old male patient with a history of RB in his left eye treated with IAC and enucleation presented to our clinic for routine RB surveillance. Radiotherapy had not been used for the treatment of his RB.

Results:

A progressive herniation of cerebellar tonsils through the foramen magnum was detected on follow-up magnetic resonance imaging (MRI). Brain and cervical MRI revealed no central nervous system mass, hydrocephalus, or syringomyelia. There was no history of head trauma.

Conclusion:

Progressive CIM may occur in unilateral sporadic RB.

Long-term outcomes of surgical management in subtypes of Chiari malformation

Objective: Chiari malformations (CMs) are a heterogeneous group of disorders defined by anatomic anomalies of the cerebellum, brainstem, and craniovertebral junction (CVJ). The aims of this study are to establish the demographic and clinical features, incidence, surgical procedures, and outcomes in large series of old and new subtypes of CMs.Material and Methods: All patients were evaluated and operated on for CM-0, 1, and 1.5 between 1985 and 2016. The patients were grouped into various subtypes. Demographic data, additional diseases, clinical features, surgical procedures, complications and outcomes were recorded.Results: 191 patients who underwent various surgical procedures were evaluated. Their mean age was 37.21 ± 9.89. We detected 15 cases of CM-0 (7.8%), 121 cases of CM-1 (63.4%), 55 cases of CM-1.5 (28.8%). In total there were 191 cases, and 220 surgical procedures were performed. 29 (13.2%) of all surgical procedure was reoperations and secondary operations. SM Cyst is found to be decreased in 72 (76.5%) patients, unchanged in 14 (14.8%) and increased in 8(8.5%) of 94 patients radiologically. Clinical outcomes are better for 131 (65.8%), same for 31 (16.2%) and worse for 9 (15%).Conclusion: This study with 172 patients is a large series that includes CM-0, 1, and 1.5 subtypes. CM-1.5 also differs for symptom presentation and durations from CM-1. There are more neurological abnormalities in patients with SM. CVD alone are an effective, useful and safe surgical procedure for CM-0, CM-1 and CM-1.5. Surgical procedure, SM existence, and symptom duration have powerful effects on outcomes.

Rare functional genetic variants in COL7A1, COL6A5, COL1A2 and COL5A2 frequently occur in Chiari Malformation Type 1

Chiari Malformation Type 1 (CM-1) is characterized by herniation of the cerebellar tonsils below the foramen magnum and the presence of headaches and other neurologic symptoms. Cranial bone constriction is suspected to be the most common biologic mechanism leading to CM-1. However, other mechanisms may also contribute, particularly in the presence of connective tissue disorders (CTDs), such as Ehlers Danlos Syndrome (EDS). Accumulating data suggest CM-1 with connective tissue disorders (CTD+) may have a different patho-mechanism and different genetic risk factors than CM-1 without CTDs (CTD-). To identify CM-1 genetic risk variants, we performed whole exome sequencing on a single large, multiplex family from Spain and targeted sequencing on a cohort of 186 unrelated adult, Caucasian females with CM-1. Targeted sequencing captured the coding regions of 21 CM-1 and EDS candidate genes, including two genes identified in the Spanish family. Using gene burden analysis, we compared the frequency of rare, functional variants detected in CM-1 cases versus publically available ethnically-matched controls from gnomAD. A secondary analysis compared the presence of rare variants in these genes between CTD+ and CTD- CM-1 cases. In the Spanish family, rare variants co-segregated with CM-1 in COL6A5, ADGRB3 and DST. A variant in COL7A1 was present in affected and unaffected family members. In the targeted sequencing analysis, rare variants in six genes (COL7A1, COL5A2, COL6A5, COL1A2, VEGFB, FLT1) were significantly more frequent in CM-1 cases compared to public controls. In total, 47% of CM-1 cases presented with rare variants in at least one of the four significant collagen genes and 10% of cases harbored variants in multiple significant collagen genes. Moreover, 26% of CM-1 cases presented with rare variants in the COL6A5 gene. We also identified two genes (COL7A1, COL3A1) for which the burden of rare variants differed significantly between CTD+ and CTD- CM-1 cases. A higher percentage of CTD+ patients had variants in COL7A1 compared to CTD+ patients, while CTD+ patients had fewer rare variants in COL3A1 than did CTD- patients. In summary, rare variants in several collagen genes are particularly frequent in CM-1 cases and those in COL6A5 co-segregated with CM-1 in a Spanish multiplex family. COL6A5 has been previously associated with musculoskeletal phenotypes, but this is the first association with CM-1. Our findings underscore the contribution of rare genetic variants in collagen genes to CM-1, and suggest that CM-1 in the presence and absence of CTD symptoms is driven by different genes.

Weak Ligaments and Sloping Joints: A New Hypothesis for Development of Congenital Atlantoaxial Dislocation and Basilar Invagination

OBJECTIVE

Developmental bony craniovertebral junction (CVJ) anomalies seem to have a genetic basis and also abnormal joint morphology causing atlantoaxial dislocation (AAD) and basilar invagination (BI).

METHODS

DNA extracted polymerase chain reaction single-stranded conformation polymorphism (SSCP) performed for mutation screening of FBN1 gene (n = 50 cases+ 50 age/sex-matched normal; total: 100). Samples with a deviated pattern of bands in SSCP were sequenced to detect the type of variation. Computed tomography (CT) scans of 100 patients (15-45 years old) compared with an equal number of age/sex-matched controls (21.9 ± 8.2 years). Joint parameters studied: sagittal joint inclination (SI), craniocervical tilt (CCT), coronal joint inclination (CI).

RESULTS

Thirty-nine samples (78%) showed sequence variants. Exon 25, 26, 27, and 28 showed variable patterns of DNA bands in SSCP, which on sequencing gives various types of DNA sequence variations in intronic region of the FBN1 gene in 14%, 14%, 6%, and 44% respectively. CT radiology:SI and CCT correlated with both BI and AAD (p < 0.01). The mean SI value in controls: 83.35° ± 8.65°, and in patients with BI and AAD:129° ± 24.05°. Mean CCT in controls: 60.2° ± 9.2°, and in patients with BI and AAD: 86.0° ± 18.1°. Mean CI in controls:110.3° ± 4.23°, and in cases: 125.15° ± 16.4°.

CONCLUSION

The study showed mutations in FBN1 gene (reported in Marfan syndrome). There is also an alteration of joint morphology, correlating with AAD and BI severity. Hence, we propose a double-hit hypothesis: the presence of weak ligaments (due to FB1 gene alterations) and abnormal joint morphology may contribute to AAD and BI.

Functional and morphological changes in hypoplasic posterior fossa

BACKGROUND

The knowledge of the development and the anatomy of the posterior cranial fossa (PCF) is crucial to define the occurrence and the prognosis of diseases where the surface and/or the volume of PCF is reduced, as several forms of craniosynostosis or Chiari type I malformation (CIM). To understand the functional and morphological changes resulting from such a hypoplasia is mandatory for their correct management. The purpose of this article is to review the pertinent literature to provide an update on this topic.

METHODS

The related and most recent literature addressing the issue of the changes in hypoplasic PCF has been reviewed with particular interest in the studies focusing on the PCF characteristics in craniosynostosis, CIM, and achondroplasia.

RESULTS AND CONCLUSIONS

In craniosynostoses, namely, the syndromic ones, PCF shows different degrees of hypoplasia, according to the different pattern and timing of early suture fusion. Several factors concur to PCF hypoplasia and contribute to the resulting problems (CIM, hydrocephalus), as the fusion of the major and minor sutures of the lambdoid arch, the involvement of the basal synchondroses, and the occlusion of the jugular foramina. The combination of these factors explains the variety of the clinical and radiological phenotypes. In primary CIM, the matter is complicated by the evidence that, in spite of impaired PCF 2D measurements and theories on the mesodermal defect, the PCF volumetry is often comparable to healthy subjects. CIM is revealed by the overcrowding of the foramen magnum that is the result of a cranio-cerebral disproportion (altered PCF brain volume/PCF total volume). Sometimes, this disproportion is evident and can be demonstrated (basilar invagination, real PCF hypoplasia); sometimes, it is not. Some recent genetic observations would suggest that CIM is the result of an excessive growth of the neural tissue rather than a reduced growth of PCF bones. Finally, in achondroplasia, both macrocephaly and reduced 2D and 3D values of PCF occur. Some aspects of this disease remain partially obscure, as the rare incidence of hydrocephalus and syringomyelia and the common occurrence of asymptomatic upper cervical spinal cord damage. On the other hand, the low rate of CIM could be explained on the basis of the reduced area of the foramen magnum, which would prevent the hindbrain herniation.

Genome-wide identification of Chiari malformation type I associated candidate genes and chromosomal variations

Chiari malformation type I (CMI) is a brain malformation that is characterized by herniation of the cerebellum into the spinal canal. Chiari malformation type I is highly heterogeneous; therefore, an accurate explanation of the pathogenesis of the disease is often not possible. Although some studies showed the role of genetics in CMI, the involvement of genetic variations in CMI pathogenesis has not been thoroughly elucidated. Therefore, in the current study we aim to reveal CMI-associated genomic variations in familial cases.Four CMI patients and 7 unaffected healthy members of two distinct families were analyzed. A microarray analysis of the affected and unaffected individuals from two Turkish families with CMI was conducted. Analyses of single nucleotide variations (SNVs) and copy number variations (CNVs) were performed by calculation of B allele frequency (BAF) and log R ratio (LRR) values from whole genome SNV data. Two missense variations, OLFML2A (rs7874348) and SLC4A9 (rs6860077), and a 5'UTR variation of COL4A1 (rs9521687) were significantly associated with CMI. Moreover, 12 SNVs in the intronic regions of FAM155A, NR3C1, TRPC7, ASTN2, and TRAF1 were determined to be associated with CMI. The CNV analysis showed that the 11p15.4 chromosome region is inherited in one of the families. The use of familial studies to explain the molecular pathogenesis of complex diseases such as CMI is crucial. It has been suggested that variations in OLFML2A, SLC4A9, and COL4A1 play a role in CMI molecular pathogenesis. The CNV analysis of individuals in both families revealed a potential chromosomal region, 11p15.4, and risk regions that are associated with CMI.

Arnold‐Chiari malformation type 1 as an unusual cause of acute respiratory failure: A case report

The authors urge clinicians to consider the possibility of Arnold‐Chiari Malformation type 1 with other central causes especially in cases where acute respiratory failure is unexplainable.

Family History in Chiari Malformation Type I: Presentation and Outcome

BACKGROUND

Some patients with Chiari malformation type I (CM-1) present with a positive family history of CM-1, the significance of which remains unknown. We aimed to study whether family history affects the clinical presentation characteristics and surgical outcome of adult patients with CM-1.

METHODS

A database of adult patients with CM-1 presenting between January 1, 2006 and December 31, 2018 was used. Presenting characteristics were compared between patients with and without a family history (first, second, or third degree) of CM-1. Among surgically treated patients, perioperative and long-term outcomes, with favorable outcome defined as a Chiari Outcome Scale score ≥14, were compared between patients with and without CM-1 family history. All patients completed at least 6 months of postoperative follow-up.

RESULTS

The database consisted of 233 adult patients with CM-1, 14 of whom (6%) had a positive family history. Presenting characteristics were comparable between patients with and without a positive family history. A total of 150 patients underwent suboccipital decompression, 12 of whom (8%) had a positive family history. After a mean follow-up of 1.9 years, patients with a family history of CM-1 were significantly less likely to achieve a favorable outcome (odds ratio, 0.22; 95% confidence interval, 0.06-0.78; P = 0.019) while controlling for several covariates. Post hoc analysis showed that the difference was most significant when looking at pain symptoms.

CONCLUSIONS

Presentation characteristics are comparable between patients with and without a family history of CM-1. Patients with a positive family history may be less likely to respond favorably to suboccipital decompression.

Epidemiology of Symptomatic Chiari Malformation in Tatarstan: Regional and Ethnic Differences in Prevalence

BACKGROUND

Epidemiology can assess the effect of Chiari I malformation (CM1) on the neurological health of a population and evaluate factors influencing CM1 development.

OBJECTIVE

To analyze the regional and ethnic differences in the prevalence of CM1.

METHODS

The population of the Republic of Tatarstan (RT) in the Russian Federation was evaluated for patients with CM1 symptoms over an 11-yr period. Typical symptoms of CM1 were found in 868 patients. Data from neurological examination and magnetic resonance imaging (MRI) measurement of posterior cranial fossa structures were analyzed.

RESULTS

MRI evidence of CM1, defined as cerebellar tonsils lying at least 5 mm inferior to the foramen magnum, was found in 67% of symptomatic patients. Another 33% of symptomatic patients had 2 to 4 mm of tonsillar ectopia, which we defined as "borderline Chiari malformation type 1 (bCM1)." The period prevalence in the entire RT for symptomatic CM1 was 20:100 000; for bCM1 was 10:100 000; and for CM1 and bCM1 together was 30:100 000. Prevalence of patients with CM1 symptoms was greater in the northern than southern districts of Tatarstan, due to a high prevalence (413:100 000) of CM1 in the Baltasy region in one of the northern districts.

CONCLUSION

One-third of patients with typical symptoms of CM1 had less than 5 mm of tonsillar ectopia (bCM1). Assessments of the health impact of CM1-type symptoms on a patient population should include the bCM1 patient group. A regional disease cluster of patients with Chiari malformation was found in Baltasy district of RT and needs further study.

Chiari malformation type I: what information from the genetics?

PURPOSE

Chiari malformation type I (CMI), a rare disorder of the craniocerebral junction with an estimated incidence of 1 in 1280, is characterized by the downward herniation of the cerebellar tonsils of at least 5 mm through the foramen magnum, resulting in significant neurologic morbidity. Classical CMI is thought to be caused by an underdeveloped occipital bone, resulting in a posterior cranial fossa which is too small to accommodate the normal-sized cerebellum. In this review, we dissect the lines of evidence supporting a genetic contribution for this disorder.

METHODS

We present the results of two types of approaches: animal models and human studies encompassing different study designs such as whole genome linkage analysis, case-control association studies, and expression studies. The update of the literature also includes the most recent findings emerged by whole exome sequencing strategy.

RESULTS

Despite evidence for a genetic component, no major genes have been identified and the genetics of CMI is still very much unknown. One major challenge is the variability of clinical presentation within CMI patient population that reflects an underlying genetic heterogeneity.

CONCLUSIONS

The identification of the genes that contribute to the etiology of CMI will provide an important step to the understanding of the underlying pathology. The finding of a predisposing gene may lead to the development of simple and accurate diagnostic tests for better prognosis, counseling, and clinical management of patients and their relatives.

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.

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.

Cerebellar tonsil ectopia measurement in type I Chiari malformation patients show poor inter-operator reliability

Background

Type 1 Chiari malformation (CM-I) has been historically defined by cerebellar tonsillar position (TP) greater than 3–5 mm below the foramen magnum (FM). Often, the radiographic findings are highly variable, which may influence the clinical course and patient outcome. In this study, we evaluate the inter-operator reliability (reproducibility) of MRI-based measurement of TP in CM-I patients and healthy controls.

Methods

Thirty-three T2-weighted MRI sets were obtained for 23 CM-I patients (11 symptomatic and 12 asymptomatic) and 10 healthy controls. TP inferior to the FM was measured in the mid-sagittal plane by seven expert operators with reference to McRae’s line. Overall agreement between the operators was quantified by intraclass correlation coefficient (ICC).

Results

The mean and standard deviation of cerebellar TP measurements for asymptomatic (CM-Ia) and symptomatic (CM-Is) patients in mid-sagittal plane was 6.38 ± 2.19 and 9.57 ± 2.63 mm, respectively. TP measurements for healthy controls was 0.48 ± 2.88 mm. The average range of TP measurements for all data sets analyzed was 7.7 mm. Overall operator agreement for TP measurements was relatively high with an ICC of 0.83.

Conclusion

The results demonstrated a large average range (7.7 mm) of measurements among the seven expert operators and support that, if economically feasible, two radiologists should make independent measurements before radiologic diagnosis of CM-I and surgery is contemplated. In the future, an objective diagnostic parameter for CM-I that utilizes automated algorithms and results in smaller inter-operator variation may improve patient selection.

Familial Chiari Type 1: A Molecular Karyotyping Study in a Turkish Family and Review of the Literature

BACKGROUND

The etiology of Chiari I malformation (CMI) has not been fully elucidated. Therefore, we performed a genetic study of a Turkish family in which 3 sisters had a diagnosis of CMI with or without syringomyelia.

METHODS

In a family with 7 children, 4 daughters complained of occipital headaches. In 2 of these daughters, CMI had been diagnosed during their 30s, and CMI plus syrinx had been diagnosed in the other daughter in her 40s. Cranial magnetic resonance imaging of the fourth daughter who had developed headaches during her 30s showed normal findings. Because the other siblings in the family were asymptomatic, radiological examinations were not performed. The family had a history of distant consanguineous marriage between parents. Additionally, the father had died, and the mother was asymptomatic, with radiologically normal findings. Array comparative genome hybridization studies were performed for 12 persons from 3 generations of this family.

RESULTS

None of the 12 cases examined harbored copy number variations.

CONCLUSIONS

This family with 3 sisters having CMI suggested a possible autosomal recessive single-gene etiology. Cases of familial CMI are unusual but important to study because they could reveal the specific genes involved in posterior fossa/foramen magnum structure and function and provide insights into the cause of sporadic cases.

Clinical Notes on Chiari Malformation

Chiari malformations (CMs) are variant structural setup of cerebellum and brain stem at the craniovertebral junction. Normally the cerebellum and parts of the brain stem lie above the foramen magnum. When the part of the cerebellum and/or brainstem protrudes into the upper spinal canal through foramen magnum, it is defined as CM. Chiari malformations may develop when part of the skull is smaller than normal or misshapen, due to which the cerebellum herniates into spinal canal through foramen magnum. This compresses the cerebellum and brainstem affecting functions controlled by these parts and blocks the flow of cerebrospinal fluid that surrounds and cushions the brain and spinal cord. Chiari malformation may cause sensory loss, ataxia, weakness, nystagmus, spastic limbs to name a few. Thus, various morbid and mortal neurologic disorders result from CM. Therefore, sound and thorough knowledge of CM and its variant anatomy are essential for diagnosis and management of neurologic disorders. Therefore, review study has been carried out for updating and consolidating the knowledge of all the variations of CMs. Literature search was carried out using databases, SciELO, ScopeMed, MEDLINE, PubMed, and Wiley Online Library. Papers containing original data were selected and secondary references retrieved from bibliographies. Various terms related to CMs were used for net surfing. The knowledge will be of immense importance to neurologists and neurosurgeons to diagnose and treat the CMs and decrease the mortality associated with CM and to radiologists for correctly interpreting the magnetic resonance imaging.

Chiari malformation type 1 presenting as unilateral progressive foot drop: a case report and review of literature

Background

Foot drop is a disabling clinical condition with multiplicity of causes, which requires detailed evaluation to identify the exact aetiology. Here, we report an extremely rare cause of foot drop in a child, which if not recognized early, could lead to multiple complications.

Case presentation

A 6-year-old girl presented with difficulty in walking and left sided foot droop for1-month duration. On examination she had reduced muscle power in dorsiflexors and plantar flexors and diminished knee and absent ankle jerk in the left side. Sensory loss was noted in L4 and L5 dermatomes on the left side. Superficial abdominal reflex was absent on the left side while preserved in the right. Nerve conduction and electromyography revealed nerve root or spinal cord cause for the foot drop. These results prompted ordering MRI spine and brain which revealed Chiari malformation type-1 with holocord syrinx extending from the cervicomedullary junction to conus medullaris.

Conclusions

This case highlights the importance of considering broad differential diagnosis for foot drop and value of the complete neurological examination including superficial reflexes in arriving at a diagnosis. Prompt diagnosis helped to early neurosurgical referral and intervention which is an important prognostic factor.

Population-based description of familial clustering of Chiari malformation Type I

OBJECTIVE

A population-based genealogical resource with linked medical data was used to define the observed familial clustering of Chiari malformation Type I (CM-I).

METHODS

All patients with CM-I were identified from the 2 largest health care providers in Utah; those patients with linked genealogical data were used to test hypotheses regarding familial clustering. Relative risks (RRs) in first-, second-, and third-degree relatives were estimated using internal cohort-specific CM-I rates; the Genealogical Index of Familiality (GIF) test was used to test for an excess of relationships between all patients with CM-I compared with the expected distribution of relationships for matched control sets randomly selected from the resource. Pedigrees with significantly more patients with CM-I than expected (p < 0.05) based on internal rates were identified.

RESULTS

A total of 2871 patients with CM-I with at least 3 generations of genealogical data were identified. Significantly increased RRs were observed for first- and third-degree relatives (RR 4.54, p < 0.001, and RR 1.36, p < 0.001, respectively); the RR for second-degree relatives was elevated, but not significantly (RR 1.20, p = 0.13). Significant excess pairwise relatedness was observed among the patients with CM-I (p < 0.001), and borderline significant excess pairwise relatedness was observed when all relationships closer than first cousins were ignored (p = 0.051). Multiple extended high-risk CM-I pedigrees with closely and distantly related members were identified.

CONCLUSIONS

This population-based description of the familial clustering of 2871 patients with CM-I provided strong evidence for a genetic contribution to a predisposition to CM-I.

Are evoked potentials clinically useful in the study of patients with Chiari malformation Type 1?

OBJECTIVE

In this study, the authors describe the brainstem auditory evoked potential (BAEP) and somatosensory evoked potential (SSEP) alterations found in a large cohort of patients with Chiari malformation Type 1 (CM-1), the relationship between the BAEPs/SSEPs and the clinical findings, the abnormalities in patients with associated syringomyelia, and the clinical and neuroradiological risk factors that are associated with abnormal evoked potentials (EPs).

METHODS

A prospectively collected database containing 545 patients with CM-1 was queried to search for patients satisfying the following criteria: 1) an age of at least 14 years, 2) neuroradiological criteria of CM-1, 3) no prior Chiari-related surgeries, and 4) preoperative EP studies conducted at the authors' institution. The 200 patients included in this cohort were classified into CM-0, CM-1, and CM-1.5 subtypes. Linear, planimetric, and angular measurements of the posterior fossa were conducted, as well as syringomyelia measurements. Two separate multiple logistic regression models were used, one to predict the covariates associated with abnormal BAEPs, and a second model to explore the variables associated with an abnormal SSEP. In these models, the BAEPs and SSEPs were dichotomized as being normal or abnormal.

RESULTS

Headaches were the main symptom in 70.5% of the patients, and Valsalva-induced headaches were most frequent in patients with CM-1 and CM-1.5 compared with patients with CM-0 (p = 0.031). BAEPs were abnormal in 38.5% of patients, and abnormal SSEPs were found in 43.5% of the entire cohort. Syringomyelia was most frequent in patients with CM-0 (64.3%) and CM-1 (51.1%) compared with those with CM-1.5 (34.7%; p = 0.03). Age (OR 1.03, 95% CI 1.00–1.06), the degree of tonsillar herniation (OR 1.08, 95% CI 1.01–1.16), and lower cranial nerve dysfunction (OR 3.99, 95% CI 1.29–14.01) had a statistically significant correlation with abnormal BAEPs. Only age (OR 1.07, 95% CI 1.04–1.10) and the degree of tonsillar herniation (OR 1.11, 95% CI 1.04–1.19) had a statistically significant correlation with abnormal SSEPs.

CONCLUSIONS

A high percentage of patients with CM-1 exhibited EP alterations regardless of their clinical or radiological findings. These findings suggest that EPs do not add any clinically relevant information nor are they helpful in establishing which symptomatic patients with CM should undergo surgical treatment. However, BAEP and SSEP studies clearly play an important role in incidentally detected patients with CM and may help to establish objective evidence of subclinical dysfunctions. In addition, neurophysiological studies may help to define subgroups of patients who require further testing and follow-up to personalize strategies for the management of incidental and oligosymptomatic patients.

Not all cases of nyctalopia are benign: Unusual and serendipitous presentation of Arnold-Chiari Type 1 malformation at a Pediatric Tertiary Care Center

The Arnold-Chiari Type 1 malformation (CM1) is a rare congenital abnormality characterized by ectopia or caudal herniation of the cerebellar tonsils through the foramen magnum into the cervical spine, resulting in crowding at the craniocervical junction. It seldom presents in childhood with symptoms and a normal neurological examination. More typically, CM1 presents in young adult women with neurological symptoms including a headache, cervical pain, cranial nerve palsies, neurosensory deficit, and ataxia. Ocular manifestations associated with Chiari I include third and sixth cranial nerve paresis and convergence/divergence abnormalities. Papilledema is a rare manifestation of Chiari I with a clinical presentation often similar to that of idiopathic intracranial hypertension. To underscore this noteworthy complication, the authors report a case of an 8-year-old boy who presented with nyctalopia and suboccipital headaches, but was diagnosed serendipitously as a case of papilledema due to Chiari I malformation.

Inheritance of Chiari-Like Malformation: Can a Mixed Breeding Reduce the Risk of Syringomyelia?

Canine Chiari-like malformation (CM) is a complex abnormality of the skull and craniocervical junction associated with miniaturization and brachycephaly which can result in the spinal cord disease syringomyelia (SM). This study investigated the inheritance of CM in a Griffon Bruxellois (GB) family and feasibility of crossbreeding a brachycephalic CM affected GB with a mesaticephalic normal Australian terrier and then backcrossing to produce individuals free of the malformation and regain GB breed characteristics. The study family cohort (n = 27) included five founder dogs from a previous baseline study of 155 GB which defined CM as a global malformation of the cranium and craniocervical junction with a shortened skull base and increased proximity of the cervical vertebrae to the skull. T1-weighted sagittal DICOM images of the brain and craniocervical junction were analysed for five significant traits (two angles, three lines) identified from the previous study and subsequent Qualitative Trait Loci analysis. Mean measurements for mixed breed, pure-breed and baseline study groups were compared. Results indicated that mixed breed traits posed less risk for CM and SM and were useful to distinguish the phenotype. Moreover on the MR images, the filial relationships displayed by the traits exhibited segregation and those presenting the greatest risk for CM appeared additive towards the severity of the condition. The external phenotypes revealed that by outcrossing breed types and with careful selection of appropriate conformation characteristics in the first generation, it is possible to regain the GB breed standard and reduce the degree of CM. The four GB affected with SM in the study all exhibited reduced caudal skull development compared to their relatives. The craniocervical traits may be useful for quantifying CM and assessing the possibility of SM thus assisting breeders with mate selection. However, such a system requires validation to ensure appropriateness for all breeds at risk.

High Incidence of Noonan Syndrome Features Including Short Stature and Pulmonic Stenosis in Patients carrying NF1 Missense Mutations Affecting p.Arg1809: Genotype-Phenotype Correlation

Neurofibromatosis type 1 (NF1) is one of the most frequent genetic disorders, affecting 1:3,000 worldwide. Identification of genotype–phenotype correlations is challenging because of the wide range clinical variability, the progressive nature of the disorder, and extreme diversity of the mutational spectrum. We report 136 individuals with a distinct phenotype carrying one of five different NF1 missense mutations affecting p.Arg1809. Patients presented with multiple café‐au‐lait macules (CALM) with or without freckling and Lisch nodules, but no externally visible plexiform neurofibromas or clear cutaneous neurofibromas were found. About 25% of the individuals had Noonan‐like features. Pulmonic stenosis and short stature were significantly more prevalent compared with classic cohorts (P < 0.0001). Developmental delays and/or learning disabilities were reported in over 50% of patients. Melanocytes cultured from a CALM in a segmental NF1‐patient showed two different somatic NF1 mutations, p.Arg1809Cys and a multi‐exon deletion, providing genetic evidence that p.Arg1809Cys is a loss‐of‐function mutation in the melanocytes and causes a pigmentary phenotype. Constitutional missense mutations at p.Arg1809 affect 1.23% of unrelated NF1 probands in the UAB cohort, therefore this specific NF1 genotype–phenotype correlation will affect counseling and management of a significant number of patients.

Joint eQTL assessment of whole blood and dura mater tissue from individuals with Chiari type I malformation

BACKGROUND

Expression quantitative trait loci (eQTL) play an important role in the regulation of gene expression. Gene expression levels and eQTLs are expected to vary from tissue to tissue, and therefore multi-tissue analyses are necessary to fully understand complex genetic conditions in humans. Dura mater tissue likely interacts with cranial bone growth and thus may play a role in the etiology of Chiari Type I Malformation (CMI) and related conditions, but it is often inaccessible and its gene expression has not been well studied. A genetic basis to CMI has been established; however, the specific genetic risk factors are not well characterized.

RESULTS

We present an assessment of eQTLs for whole blood and dura mater tissue from individuals with CMI. A joint-tissue analysis identified 239 eQTLs in either dura or blood, with 79% of these eQTLs shared by both tissues. Several identified eQTLs were novel and these implicate genes involved in bone development (IPO8, XYLT1, and PRKAR1A), and ribosomal pathways related to marrow and bone dysfunction, as potential candidates in the development of CMI.

CONCLUSIONS

Despite strong overall heterogeneity in expression levels between blood and dura, the majority of cis-eQTLs are shared by both tissues. The power to detect shared eQTLs was improved by using an integrative statistical approach. The identified tissue-specific and shared eQTLs provide new insight into the genetic basis for CMI and related conditions.

Prevalence and heritability of symptomatic syringomyelia in Cavalier King Charles Spaniels and long-term outcome in symptomatic and asymptomatic littermates

Background

Syringomyelia (SM) is common in the Cavalier King Charles Spaniel (CKCS). Dogs with syringes express clinical signs or might be clinically silent.

Objectives

To investigate the prevalence and heritability of symptomatic SM, the association between clinical signs and magnetic resonance imaging (MRI) findings, and long‐term outcome.

Animals

All CKCS registered in the Danish Kennel Club in 2001 (n = 240).

Methods

A cross‐sectional questionnaire‐based prevalence study validated by telephone interviews and clinically investigated clinical signs of SM. Dogs were 6 years at the time of investigation. A prospective observational litter study including clinical investigations, MRI and 5‐year follow‐up of symptomatic and asymptomatic siblings. Heritability was estimated based on the scale of liability in the study population and litter cohort.

Results

The cross‐sectional study estimated a prevalence of symptomatic SM at 15.4% in the population. Thirteen symptomatic and 9 asymptomatic siblings participated in the litter study. Spinal cord syringes were confirmed in 21 of 22 littermates (95%). Syrinx diameter and mean syrinx : spinal cord ratio were significantly correlated with clinical signs (P < .01). Estimated heritability of symptomatic SM was 0.81. Symptomatic SM motivated euthanasia in 20%. Dogs with syringes, which expressed no clinical signs at the age of 6, remained asymptomatic in 14/15 cases (93%).

Conclusions and Clinical Importance

The prevalence of symptomatic SM is high and genetics have a high impact on clinical disease expression. Further investigations of factors influencing the outbreak threshold of clinical signs of SM are desirable.

The Chiari malformations: a review with emphasis on anatomical traits

Hindbrain herniations come in many forms and have been further subdivided as their original descriptions. For cerebellar tonsillar ectopia, they can be divided into two categories, acquired and congenital. Acquired hindbrain herniations are due to increased intracranial pressure caused by certain conditions such as trauma or brain tumor. Although the mechanism for their formation is not clear, congenital hindbrain herniation makes up the majority of these congenital malformations. Furthermore, these malformations are often found to harbor additional anatomical derailments in addition to the hindbrain herniation whether it be the cerebellar tonsils (Chiari I malformation) or the cerebellar vermis (Chiari II malformation). This article reviews these forms of cerebellar ectopia and describes the details of their anomalous anatomy. Moreover, this article compares and contrasts the differing embryological theories found in this literature.

Identification of Chiari Type I Malformation subtypes using whole genome expression profiles and cranial base morphometrics

Background

Chiari Type I Malformation (CMI) is characterized by herniation of the cerebellar tonsils through the foramen magnum at the base of the skull, resulting in significant neurologic morbidity. As CMI patients display a high degree of clinical variability and multiple mechanisms have been proposed for tonsillar herniation, it is hypothesized that this heterogeneous disorder is due to multiple genetic and environmental factors. The purpose of the present study was to gain a better understanding of what factors contribute to this heterogeneity by using an unsupervised statistical approach to define disease subtypes within a case-only pediatric population.

Methods

A collection of forty-four pediatric CMI patients were ascertained to identify disease subtypes using whole genome expression profiles generated from patient blood and dura mater tissue samples, and radiological data consisting of posterior fossa (PF) morphometrics. Sparse k-means clustering and an extension to accommodate multiple data sources were used to cluster patients into more homogeneous groups using biological and radiological data both individually and collectively.

Results

All clustering analyses resulted in the significant identification of patient classes, with the pure biological classes derived from patient blood and dura mater samples demonstrating the strongest evidence. Those patient classes were further characterized by identifying enriched biological pathways, as well as correlated cranial base morphological and clinical traits.

Conclusions

Our results implicate several strong biological candidates warranting further investigation from the dura expression analysis and also identified a blood gene expression profile corresponding to a global down-regulation in protein synthesis.

Genetic evaluation and application of posterior cranial fossa traits as endophenotypes for Chiari type I malformation

Chiari Type I Malformation (CMI) is characterized by herniation of the cerebellar tonsils through the base of the skull. Although cerebellar tonsillar herniation (CTH) is hypothesized to result from an underdeveloped posterior cranial fossa (PF), patients are frequently diagnosed by the extent of CTH without cranial morphometric assessment. We recently completed the largest CMI whole genome qualitative linkage screen to date. Despite an initial lack of statistical evidence, stratified analyses using clinical criteria to reduce heterogeneity resulted in a striking increase in evidence for linkage. The present study focused on the use of cranial base morphometrics to further dissect this heterogeneity and increase power to identify disease genes. We characterized the genetic contribution for a series of PF traits and evaluated the use of heritable, disease-relevant PF traits in ordered subset analysis (OSA). Consistent with a genetic hypothesis for CMI, much of the PF morphology was found to be heritable and multiple genomic regions were strongly implicated from OSA, including regions on Chromosomes 1 (LOD = 3.07, p = 3 × 10(-3) ) and 22 (LOD = 3.45, p = 6 × 10(-5) ) containing several candidates warranting further investigation. This study underscores the genetic heterogeneity of CMI and the utility of PF traits in CMI genetic studies.

Association of Chiari malformation and vitamin B12 deficit in a family

PURPOSE

A clear etiology of Chiari malformation is still lacking. Some associations between this disorder and genetical variations have been reported. Documented cases of familial Chiari malformation in three consecutive generations are rare. Furthermore, an association of Chiari disorder and vitamin B12 deficit has rarely been described in literature.

METHODS

In this study, three generations of a family suffering from Chiari 1 or Chiari 0 malformation have been examined with MRI, clinically and laboratory (hemograms).

RESULTS

Chiari malformation could be confirmed in all presented patients: While the F2 generation (children: 1 × ♀, 1 × ♂) and the female F1 generation (mother and sister of mother) suffered from Chiari type 1, the male F0 generation showed Chiari 0 malformation. F0 and F1 generation further presented with syringomyelia (F0: C4-D1; F1: C4-D2). All patients except the grandfather (F0) underwent surgical posterior fossa decompression to relive successfully cerebellar and hydrocephalus associated progressing clinical symptoms. The hemograms of generation 1 and 2 revealed familial vitamin B12 deficit.

CONCLUSIONS

A hereditary component is discussed in Chiari malformation, yet proved etiology is still lacking. As folic acid plays an important role in the development of the neural tube, vitamin B12 deficit might have some impact on the development of Chiari malformations.

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.

Stratified whole genome linkage analysis of Chiari type I malformation implicates known Klippel-Feil syndrome genes as putative disease candidates

Chiari Type I Malformation (CMI) is characterized by displacement of the cerebellar tonsils below the base of the skull, resulting in significant neurologic morbidity. Although multiple lines of evidence support a genetic contribution to disease, no genes have been identified. We therefore conducted the largest whole genome linkage screen to date using 367 individuals from 66 families with at least two individuals presenting with nonsyndromic CMI with or without syringomyelia. Initial findings across all 66 families showed minimal evidence for linkage due to suspected genetic heterogeneity. In order to improve power to localize susceptibility genes, stratified linkage analyses were performed using clinical criteria to differentiate families based on etiologic factors. Families were stratified on the presence or absence of clinical features associated with connective tissue disorders (CTDs) since CMI and CTDs frequently co-occur and it has been proposed that CMI patients with CTDs represent a distinct class of patients with a different underlying disease mechanism. Stratified linkage analyses resulted in a marked increase in evidence of linkage to multiple genomic regions consistent with reduced genetic heterogeneity. Of particular interest were two regions (Chr8, Max LOD = 3.04; Chr12, Max LOD = 2.09) identified within the subset of "CTD-negative" families, both of which harbor growth differentiation factors (GDF6, GDF3) implicated in the development of Klippel-Feil syndrome (KFS). Interestingly, roughly 3-5% of CMI patients are diagnosed with KFS. In order to investigate the possibility that CMI and KFS are allelic, GDF3 and GDF6 were sequenced leading to the identification of a previously known KFS missense mutation and potential regulatory variants in GDF6. This study has demonstrated the value of reducing genetic heterogeneity by clinical stratification implicating several convincing biological candidates and further supporting the hypothesis that multiple, distinct mechanisms are responsible for CMI.

Chiari malformation type I: a case-control association study of 58 developmental genes

Chiari malformation type I (CMI) is a disorder characterized by hindbrain overcrowding into an underdeveloped posterior cranial fossa (PCF), often causing progressive neurological symptoms. The etiology of CMI remains unclear and is most likely multifactorial. A putative genetic contribution to CMI is suggested by familial aggregation and twin studies. Experimental models and human morphometric studies have suggested an underlying paraxial mesoderm insufficiency. We performed a case-control association study of 303 tag single nucleotide polymorphisms (SNP) across 58 candidate genes involved in early paraxial mesoderm development in a sample of 415 CMI patients and 524 sex-matched controls. A subgroup of patients diagnosed with classical, small-PCF CMI by means of MRI-based PCF morphometry (n = 186), underwent additional analysis. The genes selected are involved in signalling gradients occurring during segmental patterning of the occipital somites (FGF8, Wnt, and retinoic acid pathways and from bone morphogenetic proteins or BMP, Notch, Cdx and Hox pathways) or in placental angiogenesis, sclerotome development or CMI-associated syndromes. Single-marker analysis identified nominal associations with 18 SNPs in 14 genes (CDX1, FLT1, RARG, NKD2, MSGN1, RBPJ1, FGFR1, RDH10, NOG, RARA, LFNG, KDR, ALDH1A2, BMPR1A) considering the whole CMI sample. None of these overcame corrections for multiple comparisons, in contrast with four SNPs in CDX1, FLT1 and ALDH1A2 in the classical CMI group. Multiple marker analysis identified a risk haplotype for classical CMI in ALDH1A2 and CDX1. Furthermore, we analyzed the possible contributions of the most significantly associated SNPs to different PCF morphometric traits. These findings suggest that common variants in genes involved in somitogenesis and fetal vascular development may confer susceptibility to CMI.

MRI-based morphometric analysis of posterior cranial fossa in the diagnosis of chiari malformation type I

BACKGROUND AND PURPOSE

The diagnosis of Chiari malformation type I (CMI) relies on MRI identification of a tonsillar descent (TD) through the foramen magnum, reflecting the overcrowding of an underdeveloped posterior cranial fossa (PCF). However, TD occurs in some patients with normal-sized PCF and, conversely, some patients with borderline or no TD have small PCF. We thus sought to identify a set of prototypic PCF measures for the diagnosis of CMI.

METHODS

We performed nineteen measurements of the PCF on sagittal MRI of 100 cases with cerebellar TD ≥5 mm and 50 control individuals, compared the average values in both cohorts and used logistic regression to devise a probability model to predict CMI status.

RESULTS

Significant decrements were detected for several PCF-related measures in the patients' cohort. We developed a probability model that combined seven of these parameters to predict diagnosis with 93% sensitivity and 92% specificity.

CONCLUSIONS

The addition of simple morphometric measurements in the diagnostic work-up of patients with suspected CMI may facilitate radiological diagnosis. Moreover, identification of the subset of CMI that arise from basichondrocranium underdevelopment is important for both, selection of the most appropriate therapeutic approach as well as proper CMI categorization in research studies.

Surgical Treatment of Chiari I Malformation—Analysis of Intraoperative Findings, Complications, and Outcome for 371 Foramen Magnum Decompressions

BACKGROUND:

Foramen magnum decompression is widely accepted as the treatment of choice for Chiari I malformation. However, important surgical details of the procedure are controversial.

OBJECTIVE:

This study analyzes 371 decompressions focusing on intraoperative findings, analysis of complications, and long-term outcomes.

METHODS:

Among 644 patients between 1985 and 2010, 359 patients underwent 371 decompressions. Surgery for symptomatic patients consisted of suboccipital craniectomy, C1 laminectomy, arachnoid dissection, and duraplasty. Short-term results were determined after 3 months; long-term outcomes were evaluated with Kaplan-Meier statistics.

RESULTS:

The mean age was 40 ± 16 years; mean follow-up was 49 ± 56 months; 75.8% demonstrated syringomyelia. The complication rate was 21.8% with permanent surgical morbidity of 3.2% and surgical mortality of 1.3%. Of the patients, 73.6% reported improvement after 3 months; 21% were unchanged. Overall, 14.3% demonstrated a neurological deterioration within 5 years and 15.4% within 10 years. The severity of neurological symptoms correlated with the grade of arachnoid pathology. Outcome data correlated with the number of previous decompressions, severity of arachnoid pathology, handling of the arachnoid, type of duraplasty, and surgical experience. First-time decompressions with arachnoid dissection and an alloplastic duraplasty resulted in surgical morbidity for 2.0%, a 0.9% mortality rate, postoperative improvement after 3 months for 82%, and neurological recurrence rates of 7% after 5 years and 8.7% after 10 years.

CONCLUSION:

Arachnoid pathology in Chiari I malformation has an impact on clinical symptoms and postoperative results. Decompressions with arachnoid dissection and an alloplastic duraplasty performed by surgeons experienced with this pathology offer a favorable long-term prognosis.

A further contribution to the delineation of the 17q21.31 microdeletion syndrome: central nervous involvement in two Italian patients

The 17q21.31 microdeletion syndrome is a genetic disorder characterized by intellectual disability, facial dysmorphisms and a typical behavioral phenotype. Patients are usually described as friendly and cooperative but they can also show behavioral problems such as hyperactivity, bad humor, temper tantrums and poor interaction. Central nervous system involvement includes callosal dysgenesis/absence, enlargement of lateral ventricles and abnormalities of cyngulate gyrus. We report on two Italian patients with the 17q21.31 microdeletion syndrome better emphasizing neuroimaging and neuropsychological characteristics. In particular, we carried out an assessment of intellectual efficiency and behavior that turned out to be within the mild-moderate range of mental retardation, as already reported in the literature. To the best of our knowledge this is the first report of a patient with the 17q21.31 microdeletion and a Chiari malformation type 1 coexisting with a mild anomaly of medulla oblongata. This malformation should be considered in patients with the 17q21.31 microdeletion syndrome, presenting suggestive symptoms (headache, neck pain, cerebellar signs or muscle weakness).

Clinical, radiological, and genetic similarities between patients with Chiari Type I and Type 0 malformations

OBJECT

Although Chiari Type I (CM-I) and Type 0 (CM-0) malformations have been previously characterized clinically and radiologically, there have been no studies focusing on the possible genetic link between these disorders. The goal of this study was to identify families in whom CM-0 and CM-I co-occurred and to further assess the similarities between these disorders.

METHODS

Families were ascertained through a proband with CM-I. Detailed family histories were obtained to identify first-degree relatives diagnosed with CM-0. Several criteria were used to exclude individuals with acquired forms of CM-I and/or syringomyelia. Individuals were excluded with syndromic, traumatic, infectious, or tumor-related syringomyelia, as well as CM-I due to a supratentorial mass, hydrocephalus, history of cervical or cranial surgery unrelated to CM-I, or development of symptoms following placement of a lumbar shunt. Medical records and MR images were used to characterize CM-I and CM-0 individuals clinically and radiologically.

RESULTS

Five families were identified in which the CM-I proband had a first-degree relative with CM-0. Further assessment of affected individuals showed similar clinical and radiological features between CM-0 and CM-I individuals, although CM-I patients in general had more severe symptoms and skull base abnormalities than their CM-0 relatives. Overall, both groups showed improvement in symptoms and/or syrinx size following craniocervical decompression surgery.

CONCLUSIONS

There is accumulating evidence suggesting that CM-0 and CM-I may be caused by a common underlying developmental mechanism. The data in this study are consistent with this hypothesis, showing similar clinical and radiological features between CM-0 and CM-I individuals, as well as the occurrence of both disorders within families. Familial clustering of CM-0 and CM-I suggests that these disorders may share an underlying genetic basis, although additional epigenetic and/or environmental factors are likely to play an important role in the development of CM-0 versus CM-I.

Familial Chiari malformation: case series

Chiari malformations (Types I-IV) are abnormalities of the posterior fossa that affect the cerebellum, brainstem, and the spinal cord with prevalence rates of 0.1%-0.5%. Case reports of familial aggregation of Chiari malformation, twin studies, cosegregation of Chiari malformation with known genetic conditions, and recent gene and genome-wide association studies provide strong evidence of the genetic underpinnings of familial Chiari malformation. The authors report on a series of 3 family pairs with Chiari malformation Type I: 2 mother-daughter pairs and 1 father-daughter pair. The specific genetic causes of familial Chiari malformation have yet to be fully elucidated. The authors review the literature and discuss several candidate genes. Recent advances in the understanding of the genetic influences and pathogenesis of familial Chiari malformation are expected to improve management of affected patients and monitoring of at-risk family members.