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Two distinct populations of Chiari I malformation based on presence or absence of posterior fossa crowdedness on magnetic resonance imaging.
J Neurosurg. 2017 Jun; 126(6):1934-1940.JN

Abstract

OBJECTIVE

A subset of patients with Chiari I malformation demonstrate patent subarachnoid spaces around the cerebellum, indicating that reduced posterior fossa volume alone does not account for tonsillar descent. The authors distinguish two subsets of Chiari I malformation patients based on the degree of "posterior fossa crowdedness" on MRI.

METHODS

Two of the coauthors independently reviewed the preoperative MR images of 49 patients with Chiari I malformation and categorized the posterior fossa as "spacious" or "crowded." Volumetric analysis of posterior fossa structures was then performed using open-source DICOM software. The preoperative clinical and imaging features of the two groups were compared.

RESULTS

The posterior fossae of 25 patients were classified as spacious and 20 as crowded by both readers; 4 were incongruent. The volumes of the posterior fossa compartment, posterior fossa tissue, and hindbrain (posterior fossa tissue including herniated tonsils) were statistically similar between the patients with spacious and crowed subtypes (p = 0.33, p = 0.17, p = 0.20, respectively). However, patients in the spacious and crowded subtypes demonstrated significant differences in the ratios of posterior fossa tissue to compartment volumes as well as hindbrain to compartment volumes (p = 0.001 and p = 0.0004, respectively). The average age at surgery was 29.2 ± 19.3 years (mean ± SD) and 21.9 ± 14.9 years for spacious and crowded subtypes, respectively (p = 0.08). Syringomyelia was more prevalent in the crowded subtype (50% vs 28%, p = 0.11).

CONCLUSIONS

The authors' study identifies two subtypes of Chiari I malformation, crowded and spacious, that can be distinguished by MRI appearance without volumetric analysis. Earlier age at surgery and presence of syringomyelia are more common in the crowded subtype. The presence of the spacious subtype suggests that crowdedness alone cannot explain the pathogenesis of Chiari I malformation in many patients, supporting the need for further investigation.

Authors+Show Affiliations

Department of Neurological Surgery, University of Virginia Health System, Charlottesville, Virginia.Department of Neurological Surgery, University of Virginia Health System, Charlottesville, Virginia.Department of Neurological Surgery, University of Virginia Health System, Charlottesville, Virginia.Department of Neurological Surgery, University of Virginia Health System, Charlottesville, Virginia.

Pub Type(s)

Journal Article

Language

eng

PubMed ID

27588590

Citation

Taylor, Davis G., et al. "Two Distinct Populations of Chiari I Malformation Based On Presence or Absence of Posterior Fossa Crowdedness On Magnetic Resonance Imaging." Journal of Neurosurgery, vol. 126, no. 6, 2017, pp. 1934-1940.
Taylor DG, Mastorakos P, Jane JA, et al. Two distinct populations of Chiari I malformation based on presence or absence of posterior fossa crowdedness on magnetic resonance imaging. J Neurosurg. 2017;126(6):1934-1940.
Taylor, D. G., Mastorakos, P., Jane, J. A., & Oldfield, E. H. (2017). Two distinct populations of Chiari I malformation based on presence or absence of posterior fossa crowdedness on magnetic resonance imaging. Journal of Neurosurgery, 126(6), 1934-1940. https://doi.org/10.3171/2016.6.JNS152998
Taylor DG, et al. Two Distinct Populations of Chiari I Malformation Based On Presence or Absence of Posterior Fossa Crowdedness On Magnetic Resonance Imaging. J Neurosurg. 2017;126(6):1934-1940. PubMed PMID: 27588590.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Two distinct populations of Chiari I malformation based on presence or absence of posterior fossa crowdedness on magnetic resonance imaging. AU - Taylor,Davis G, AU - Mastorakos,Panagiotis, AU - Jane,John A,Jr AU - Oldfield,Edward H, Y1 - 2016/09/02/ PY - 2016/9/3/pubmed PY - 2019/8/27/medline PY - 2016/9/3/entrez KW - Chiari I malformation KW - HR = herniated tissues (tonsils) not confined to the posterior fossa compartment KW - PFC + HR = total hindbrain content contained within the posterior fossa and the component that has herniated KW - PFC = volume of the tissue contents within the posterior fossa compartment KW - PFV = posterior fossa volume KW - diagnostic and operative techniques KW - posterior fossa decompression KW - posterior fossa volume KW - syringomyelia SP - 1934 EP - 1940 JF - Journal of neurosurgery JO - J Neurosurg VL - 126 IS - 6 N2 - OBJECTIVE A subset of patients with Chiari I malformation demonstrate patent subarachnoid spaces around the cerebellum, indicating that reduced posterior fossa volume alone does not account for tonsillar descent. The authors distinguish two subsets of Chiari I malformation patients based on the degree of "posterior fossa crowdedness" on MRI. METHODS Two of the coauthors independently reviewed the preoperative MR images of 49 patients with Chiari I malformation and categorized the posterior fossa as "spacious" or "crowded." Volumetric analysis of posterior fossa structures was then performed using open-source DICOM software. The preoperative clinical and imaging features of the two groups were compared. RESULTS The posterior fossae of 25 patients were classified as spacious and 20 as crowded by both readers; 4 were incongruent. The volumes of the posterior fossa compartment, posterior fossa tissue, and hindbrain (posterior fossa tissue including herniated tonsils) were statistically similar between the patients with spacious and crowed subtypes (p = 0.33, p = 0.17, p = 0.20, respectively). However, patients in the spacious and crowded subtypes demonstrated significant differences in the ratios of posterior fossa tissue to compartment volumes as well as hindbrain to compartment volumes (p = 0.001 and p = 0.0004, respectively). The average age at surgery was 29.2 ± 19.3 years (mean ± SD) and 21.9 ± 14.9 years for spacious and crowded subtypes, respectively (p = 0.08). Syringomyelia was more prevalent in the crowded subtype (50% vs 28%, p = 0.11). CONCLUSIONS The authors' study identifies two subtypes of Chiari I malformation, crowded and spacious, that can be distinguished by MRI appearance without volumetric analysis. Earlier age at surgery and presence of syringomyelia are more common in the crowded subtype. The presence of the spacious subtype suggests that crowdedness alone cannot explain the pathogenesis of Chiari I malformation in many patients, supporting the need for further investigation. SN - 1933-0693 UR - https://www.unboundmedicine.com/medline/citation/27588590/Two_distinct_populations_of_Chiari_I_malformation_based_on_presence_or_absence_of_posterior_fossa_crowdedness_on_magnetic_resonance_imaging_ L2 - https://thejns.org/doi/10.3171/2016.6.JNS152998 DB - PRIME DP - Unbound Medicine ER -