Tag: posterior cranial fossa

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Morphometric assessment of the posterior cranial fossa and its contents in patients with chiari malformation type I and type 0

Acta Neurochirurgica (2026) 168:117

This study presents a retrospective, landmark-based morphometric analysis of the clivus, tentorium, and posterior cranial fossa on midsagittal MRI in 326 subjects, comparing Chiari malformation Type I (CM-I), Chiari Type 0 (CM-0), and matched controls. Key measured parameters include clivus length and angle, tentorial angle, foramen magnum diameter, and area-based ratios relating cerebellum, posterior fossa, and intracranial cavity.

Findings indicate that CM-I patients exhibit clival shortening, reduced posterior cranial fossa area, altered tentorial orientation, and increased cerebellar occupancy relative to posterior fossa and brain, whereas CM-0 patients show morphometry comparable to controls. The authors conclude CM-I has distinct morphoanatomical remodeling, while CM-0 may represent a functional clinical entity without consistent structural substrate.

Definitions: CM-I is defined by ≥5 mm cerebellar tonsillar descent below the foramen magnum on MRI, while CM-0 is defined by <3 mm descent despite Chiari-like symptoms.

Design: Retrospective mid-sagittal MRI morphometry of 326 adults (CM-I n=111, CM-0 n=27, controls n=188) using multiple cranial base, posterior fossa, cerebellar, and intracranial measurements plus area-based ratios.

Key CM-I anatomy: Compared with CM-0 and controls, CM-I showed shorter clivus length, smaller posterior cranial fossa area, and larger cerebellar area; foramen magnum diameter and total brain area were similar across groups.

Crowding ratios: CM-I had higher cerebellum/posterior fossa and cerebellum/brain area ratios, indicating increased relative cerebellar occupancy despite preserved global cranial proportions.

CM-0 vs controls: CM-0 morphometric measurements were largely comparable to healthy controls, with no consistent structural differences in the main posterior fossa metrics highlighted.

Interpretation: CM-I aligns with a pattern of cranial base remodeling and posterior fossa insufficiency, whereas CM-0 may be better viewed as a functionally defined condition rather than one with a consistent structural substrate.

Reliability/statistics: Analyses used nonparametric tests (Kruskal–Wallis with Bonferroni-corrected Mann–Whitney post hoc), and interobserver measurement reliability was good–excellent (ICC 0.82–0.94).

Limitations: Morphometry was 2D mid-sagittal (not full 3D volumetry) and CSF flow dynamics (e.g., phase-contrast MRI) were not uniformly available, limiting functional assessment—especially relevant to CM-0.

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Posterior cranial fossa and cervical spine morphometric abnormalities in symptomatic Chiari type 0 and Chiari type 1 malformation patients with and without syringomyelia

Acta Neurochirurgica (2021) 163:3051–3064

To better understand how anatomical features of Chiari malformation type 0 (CM0) result in the manifestation of Chiari malformation type 1 (CM1) signs and symptoms, we conducted a morphometric study of the posterior cranial fossa (PCF) and cervical canal in patients with CM1 and CM0.

Methods This retrospective study had a STROBE design and included 120 adult patients with MRI evidence of a small PCF (SPCF), typical clinical symptoms of CM1, and a diagnosis of CM1, CM0, or SPCF-TH0-only (SPCF with cerebellar ectopia less than 2 mm and without syringomyelia). Patients were divided by MRI findings into 4 groups: SPCF-TH0-only, SPCF-TH0-syr (CM0 with SPCF and syringomyelia), SPCF-CM1-only (SPCF with cerebellar ectopia 5 mm or more without syringomyelia), and SPCF-CM1-syr (CM1 with syringomyelia). Neurological examination data and MRI parameters were analyzed.

Results All patient cohorts had morphometric evidence of a small, flattened, and overcrowded PCF. The PCF phenotype of the SPCF-TH0-only group differed from that of other CM cohorts in that the length of clivus and supraocciput and the height of the PF were longer, the upper CSF spaces of PCF were taller, and the area of the foramen magnum was smaller. The SPCF-TH0 groups had a more significant narrowing of the superior cervical canal and a smaller decrease in PCF height than the SPCF-CM1 groups.

Conclusions Patients with SPCF-TH0 with and without syringomyelia developed Chiari 1 symptoms and signs. Patients with SPCF-TH0-syr (Chiari 0) had more constriction of their CSF pathways in and around the foramen magnum than patients with SPCF-TH0-only.

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Efficacy and safety of gamma knife radiosurgery for posterior cranial fossa meningioma

Neurosurgical Review (2020) 43:1089–1099

The management of posterior cranial fossa meningioma [PCFM] is challenging and many neurosurgeons advise gamma knife radiosurgery [GKRS] as a modality for its upfront or adjuvant treatment. Due to the varying radiosurgical response based on lesion location, tumor biology, and radiation dosage, we performed a pioneer attempt in doing a systematic review analyzing the treatment efficacy and safety profile of GKRS for PCFM based on current literature.

A systematic review was performed according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses [PRISMA] guidelines. A thorough literature search was conducted on PubMed, Web of science, and Cochrane data base; articles were selected systematically based on PRISMA protocol, reviewed completely, and relevant data was summarized and discussed.

A total of 18 publications pertaining to GKRS for PCFM were included with a pooled sample size of 2131 patients. The median pre-GKRS tumor volume ranged from 2.28 to 10.5 cm [3]. Primary GKRS was administered in 61.1% of the pooled study cohorts, adjuvant treatment in 32.9%, and salvage therapy in 6.5% patients. Majority of the meningiomas were WHO grade 1 tumors (99.7%). The pooled mean marginal dose in the studies was 13.6 Gy (range 12–15.2 Gy) while the mean of maximum doses was 28.6 Gy (range 25–35 Gy). Most studies report an excellent radiosurgical outcome including the tumor control rate and the progression-free survival [PFS] of over 90%. The tumor control, PFS, and adverse radiation effect [ARE] rates in author’s series were 92.3%, 91%, and 9.6%, respectively. The favorable radiosurgical outcome depends on multiple factors such as small tumor volume, absence of previous radiotherapy, tumor location, elderly patients, female gender, longer time from symptom onset, and decreasing maximal dose.

GKRS as primary or adjuvant treatment modality needs to be considered as a promising management strategy for PCFM in selected patients in view of the growing evidence of high tumor control rate, improved neurological functions, and low incidence of ARE. The use of multiple isocenters, 3-D image planning, and limit GKRS treatment to tumors less than 3.5 cm help to avoid complications and achieve the best results. The treatment decisions in PCFM cases must be tailored and should consider the factors such as radiological profile, symptom severity, performance level, and patient preference for a good outcome.

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Endoscopic Third Ventriculostomy for the Management of Chiari I and Related Hydrocephalus: Outcome and Pathogenetic Implications

Neurosurgery 68:950–956, 2011 DOI: 10.1227/NEU.0b013e318208f1f3

Hydrocephalus affects 7% to 10% of patients with Chiari I malformation (CIM). It can be successfully treated by endoscopic third ventriculostomy (ETV), possibly improving related CIM and syringomyelia.

OBJECTIVE: To confirm the effectiveness of ETV in the management of Chiari-related hydrocephalus and symptoms and to estimate the posterior cranial fossa volume (PCFV) to find the possible reasons for the success or failure of ETV.

METHODS: Fifteen patients (11 children and 4 adults) underwent ETV for hydrocephalus associated with CIM (syringomyelia was present in 6 patients). Preoperative PCFV, posterior fossa brain volume (PFBV), and PFBV/PCFV ratio were calculated in the last 12 patients in the series by a magnetic resonance imaging–based computerized method.

RESULTS: All patients had symptomatic hydrocephalus (mean third ventricle diameter, 14.1 mm). Mean tonsillar ectopia was 12.7 mm. Postoperatively, hydrocephalus symptoms improved in all cases (mean third ventricle diameter, 8.3 mm); signs and symptoms of CIM and syringomyelia resolved or improved in all patients, although the malformation remained radiologically stable in half of the patients (postoperative mean tonsillar ectopia, 8.8 mm). There were no remarkable differences between cases and controls with regard to PCFV and PFBV. The PFBV/PCFV ratio was comparable in pediatric cases and controls but not among adult patients, suggesting a PCF overcrowding in the controls.

CONCLUSION: ETV is an effective treatment for hydrocephalus associated with CIM. It is successful in improving CIM and syringomyelia in patients with no overcrowding (mainly in children) or with reversible overcrowding of the PCF (mainly in adults).

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Mechanisms of cerebellar tonsil herniation in patients with Chiari malformations as guide to clinical management

Acta Neurochir (2010) 152:1117–1127.DOI 10.1007/s00701-010-0636-3

The pathogenesis of Chiari malformations is incompletely understood. We tested the hypothesis that different etiologies have different mechanisms of cerebellar tonsil herniation (CTH), as revealed by posterior cranial fossa (PCF) morphology.

Methods In 741 patients with Chiari malformation type I (CM-I) and 11 patients with Chiari malformation type II (CM-II), the size of the occipital enchondrium and volume of the PCF (PCFV) were measured on reconstructed 2D-CT and MR images of the skull. Measurements were compared with those in 80 age- and sex-matched healthy control individuals, and the results were correlated with clinical findings.

Results Significant reductions of PCF size and volume were present in 388 patients with classical CM-I, 11 patients with CM-II, and five patients with CM-I and craniosynostosis. Occipital bone size and PCFV were normal in 225 patients with CM-I and occipitoatlantoaxial joint instability, 55 patients with CM-I and tethered cord syndrome (TCS), 30 patients with CM-I and intracranial mass lesions, and 28 patients with CM-I and lumboperitoneal shunts. Ten patients had miscellaneous etiologies. The size and area of the foramen magnum were significantly smaller in patients with classical CM-I and CM-I occurring with craniosynostosis and significantly larger in patients with CM-II and CM-I occurring with TCS.

Conclusions Important clues concerning the pathogenesis of CTH were provided by morphometric measurements of the PCF. When these assessments were correlated with etiological factors, the following causal mechanisms were suggested: (1) cranial constriction; (2) cranial settling; (3) spinal cord tethering; (4) intracranial hypertension; and (5) intraspinal hypotension

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Basioccipital hypoplasia in Chiari malformation Type I

J Neurosurg 111:1046–1052, 2009. DOI: 10.3171/2009.2.JNS08284

The chronic tonsillar herniation defining Chiari malformation Type I (CMI) is thought to result from overcrowding of a normally developing hindbrain within a congenitally small posterior cranial fossa (PCF) due to occipital hypoplasia. The goals in the present study were to authenticate the cranioencephalic disproportion in a group of patients with CMI and to discuss new developmental aspects according to which part of the occipital bone was underdeveloped.

Methods. The authors retrospectively examined a group of 17 patients with CMI. Measurements of osteotento- rial and neural structures of the PCF were made on MR images of the brain. The results were compared with findings in 30 healthy controls by using the Mann-Whitney U-test.

Results. Dimensions of the neural structures did not differ between the 2 groups of patients. The mean length of the basiocciput was significantly shorter in the CMI group (19.4 mm) compared with the control group (25.7 mm; p = 0.0003). The mean diameter of the foramen magnum was larger in the CMI group, but this difference was not statistically significant. The dimensions of the supraocciput and the mean angle of the cerebellar tentorium were identical in the 2 groups.

Conclusions. Data in this study support the idea that occipital hypoplasia is the main cause of overcrowding within the PCF. Basioccipital shortness is a cardinal feature of the resultant shallow PCF and could proceed from a congenital disorder of the cephalic mesoderm of the parachordal plate or occur later in the infancy because of prema- ture stenosis of the sphenooccipital synchondrosis

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