Chiari type 1 deformity

• A Novel Metric for Assessing Long-Term Outcomes in Adults with Chiari Malformation Type I: Occipitocervical Dura Angulation (ODA)-Applications and Value
• Vogt Koyanagi Harada disease with bilateral disc edema diagnosed as Arnold Chiari malformation with papilledema: The blurred margin between ophthalmology and neurology
• Using Patient-Reported Outcome Measures for Adult Chiari Malformation Type 1
• Surgical Treatment of Basilar Invagination without Evident Atlantoaxial Instability (Type B) - A Systematic Review
• Chiari III Malformation: Quantification of Long-term Outcome After Early Surgery
• Difference in clinical presentation and surgical outcomes in pediatric and adult patients with Chiari malformation type 1: a single center retrospective study
• Substantiated degeneration of rectus capitis posterior minor muscle in Chiari malformation I based on multimodal observations: a prospective cohort study
• Impact of surgical timing and concomitant anomalies on neonatal meningomyelocele outcomes: a single-center experience

Chiari type 1 deformity is a hindbrain disorder associated with elongation of the cerebellar tonsils, which descend below the foramen magnum into the spinal canal.

Defined as cerebellar tonsillar herniation ≥ 5 mm below the foramen magnum ¹⁾.

The hindbrain is not malformed but deformed. Accordingly, “Chiari type 1 deformity,” not “Chiari type 1 malformation” is the correct term to characterize primary tonsillar herniation.

● a heterogeneous entity with the common feature of impaired cerebrospinal fluid circulation through the foramen magnum

● may be congenital or acquired

● evaluation: MRI of the brain and cervical spine (to R/O syringomyelia). Cine MRI to evaluate CSF flow through foramen magnum in uncertain cases

● cerebellar tonsillar herniation on MRI: criteria vary, > 5 mm below the foramen magnum is often cited, but is neither essential nor diagnostic of the condition

● treatment, when indicated, is surgical, but aspects of what that surgery should entail are controversial (enlargement of the foramen magnum is usually involved)

● associated with syringomyelia in 30–70%, which almost always improves with treatment of the Chiari malformation.

AKA primary cerebellar ectopia, AKA adult Chiari malformation (since it tends to be diagnosed in the 2nd or 3rd decade of life). A heterogeneous group of conditions, with the underlying commonality of disruption of normal CSF flow through the foramen magnum (FM). Some cases are congenital, but others are acquired (this section is kept here under developmental for historical and organizational reasons). Classically described as a rare abnormality restricted to a caudal displacement of cerebellum with tonsillar herniation below the foramen magnum (below for criteria) and “peg-like elongation of tonsils.” Unlike Chiari type 2, the medulla is not caudally displaced (some authors disagree on this point), the brainstem is not involved, lower cranial nerves are not elongated, and upper cervical nerves do not course cephalad. Syringomyelia of the spinal cord is present in 30–70% of cases.

Hydromyelia probably doesn’t occur; CSF flow has not been documented in humans, and it is generally not possible to find communication between the syrinx and the central canal in Chiari 1 patients. Hydrocephalus occurs in 7–9% of patients with Chiari type 1 malformation and syringomyelia.

Cerebellar tonsil descent below FM with impaction, while common, is no longer a sine qua non of diagnosis.

Chiari type 1 deformity is commonly seen in pediatric neurology, neuroradiology, and neurosurgery and may have various clinical presentations depending on patient age. In addition, Chiari type 1 deformity is increasingly found by neuroimaging studies as an incidental finding in asymptomatic children ²⁾.

In the past, it was estimated that the condition occurs in about one in every 1,000 births. However, the increased use of diagnostic imaging has shown that CM may be much more common. Complicating this estimation is the fact that some children who are born with the condition may not show symptoms until adolescence or adulthood, if at all. CMs are more prevalent in certain groups, including people of Celtic descent.

A statistically significant (P = .03) female predominance of the malformation was observed, with a female: male ratio of approximately 3:2.

Associated skeletal anomalies were seen in 24% of patients.

Syringomyelia was detected in 40% of patients, most commonly between the C-4 and C-6 levels. Of the 25 patients who presented with spinal symptoms, 23 (92%) proved to have a syrinx at MR imaging. When the syrinx extended into the medulla (n = 3), however, brainstem symptoms predominated. Patients with objective brain stem or cerebellar syndrome had the largest mean tonsillar herniations. Patients with tonsillar herniations greater than 12 mm were invariably symptomatic, but approximately 30% of patients with tonsils herniating 5-10 mm below the foramen magnum were asymptomatic at MR imaging. “Incidental” Chiari I malformations are thus much more common than previously recognized, and careful clinical assessment remains the cornerstone for proper diagnosis and management ³⁾.

Chiari type 1 deformity classification.

see Chiari type 1 deformity etiology.

Chiari malformation Type I (CM-I) related to syndromic craniosynostosis in pediatric patients has been well-studied. The surgical management consists of cranial vault remodeling with or without posterior fossa decompression. There were also cases, in whom CM-I was diagnosed prior to the craniosynostosis in early childhood.

A 16-year-old boy who admitted with symptoms related to CM-I. With careful examination and further genetic investigations, a diagnosis of Crouzon syndrome was made, of which the patient and his family was unaware before. The patient underwent surgery for posterior fossa decompression and followed-up for Crouzon's syndrome.

This is the only case report indicating a late adolescent diagnosis of Crouzon syndrome through clinical symptoms of an associated CM-I ⁴⁾.

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 Healthcare 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 ⁵⁾.

The pathophysiology of CMI is poorly understood and it remains unknown how ICP alterations relate to symptoms and radiological findings.

There is some evidence of impaired intracranial compliance as an important pathophysiological mechanism ⁶⁾.

Magnetic resonance imaging measurement of transcranial CSF flow and blood flow may lead to a better understanding of the pathophysiology of Chiari malformations and may prove to be an important diagnostic tool for guiding for the treatment of patients with Chiari I malformation ⁷⁾.

The pathogenesis of a Chiari I malformation of the cerebellar tonsils is grouped into 4 general mechanisms. ⁸⁾.

It appears that the pathogenesis of Chiari malformation with or without associated basilar invagination and/or syringomyelia is primarily related to atlantoaxial instability. The data suggest that the surgical treatment in these cases should be directed toward atlantoaxial stabilization and segmental arthrodesis. Except in cases in which there is assimilation of the atlas, inclusion of the occipital bone is neither indicated nor provides optimum stability. Foramen magnum decompression is not necessary and may be counter-effective in the long run ⁹⁾. 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.

Patients with Chiari malformation type 1 (CMI) often present with elevated pulsatile and static intracranial pressure (ICP).

Several lines of evidence suggest common pathophysiological mechanisms in Chiari malformation Type I (CMI) and idiopathic intracranial hypertension (IIH). It has been hypothesized that tonsillar ectopy, a typical finding in CMI, is the result of elevated intracranial pressure (ICP) combined with a developmentally small posterior cranial fossa (PCF).

The study of Frič and Eide showed comparable and elevated pulsatile intracranial pressure, indicative of impaired intracranial compliance, in both CMI and IIH cohorts, while static ICP was higher in the IIH cohort. The data did not support the hypothesis that reduced PCFV combined with increased ICP causes tonsillar ectopy in CMI. Even though impaired intracranial compliance seems to be a common pathophysiological mechanism behind both conditions, the mechanisms explaining the different clinical and radiological presentations of CMI and IIH remain undefined ¹⁰⁾.

see Chiari type 1 deformity Natural history.

see Chiari type 1 deformity clinical features.

Along with tonsillar herniation, imaging studies have documented additional abnormalities, including smaller and overcrowded posterior cranial fossa ^{11) 12) 13) 14) 15)}.

MRI Findings After Surgery for Chiari Malformation Type I is important when evaluating postoperative changes ¹⁶⁾.

Sagittal MRI overestimates the degree of tonsillar ectopia. Misdiagnosis may occur if sagittal imaging alone is used. The cerebellar tonsils are paramedian structures, and this should be kept in mind when interpreting midline sagittal MRI.

Chiari type 2 malformation

Chiari type 1 deformity treatment.

see Chiari type 1 deformity outcome.

Chicago Chiari Outcome Scale (CCOS)

There is currently no consensus on the safety of sports participation for patients with Chiari I malformation (CM-I).

A prospective survey was administered to 503 CM-I patients at 2 sites over a 46-month period. Data were gathered on imaging characteristics, treatment, sports participation, and any sport-related injuries. Additionally, 81 patients completed at least 1 subsequent survey following their initial entry into the registry and were included in a prospective group, with a mean prospective follow-up period of 11 months.

Of the 503 CM-I patients, 328 participated in sports for a cumulative duration of 4641 seasons; 205 of these patients participated in contact sports. There were no serious or catastrophic neurological injuries. One patient had temporary extremity paresthesias that resolved within hours, and this was not definitely considered to be related to the CM-I. In the prospective cohort, there were no permanent neurological injuries.

No permanent or catastrophic neurological injuries were observed in CM-I patients participating in athletic activities. The authors believe that the risk of such injuries is low and that, in most cases, sports participation by children with CM-I is safe ¹⁷⁾.

Chiari type 1 deformity systematic reviews and meta-analysis.

see Chiari type 1 deformity case series.

see Chiari type 1 deformity case reports.