Ventrolateral Tonsillar Position Defines Novel Chiari 0.5 Classification.

TitleVentrolateral Tonsillar Position Defines Novel Chiari 0.5 Classification.
Publication TypeJournal Article
Year of Publication2020
AuthorsMorgenstern PF, Tosi U, Uribe-Cardenas R, Greenfield JP
JournalWorld Neurosurg
Date Published2020 Apr
KeywordsArnold-Chiari Malformation, Child, Preschool, Conservative Treatment, Cranial Fossa, Posterior, Decompression, Surgical, Encephalocele, Female, Follow-Up Studies, Humans, Infant, Magnetic Resonance Imaging, Male, Medulla Oblongata, Palatine Tonsil, Retrospective Studies, Treatment Outcome

BACKGROUND: Cervicomedullary compression in young children has been described in the context of Chiari type 1 malformation, with symptoms associated with the extent of tonsillar herniation below McRae line. Historically, Chiari type 1 malformation has been defined by tonsillar herniation of at least 5 mm. However, in certain populations, including very young children, Chiari symptoms may be present without this finding. A new Chiari classification is thus necessary.

METHODS: Cases involving patients up to 5 years of age evaluated for possible posterior fossa decompression were retrospectively reviewed. Preoperative symptoms, magnetic resonance imaging findings, surgical management, and short- and long-term outcome and follow-up were recorded. Tonsillar descent and presence of ventral herniation (VH) were recorded. We define VH as the tonsils crossing a line that bisects the caudal medulla at the level of the foramen magnum, thus creating a novel entity, Chiari type 0.5 malformation. Patients with ventrally herniated tonsils were compared with patients exhibiting more typical Chiari morphology.

RESULTS: Of 41 cases retrospectively reviewed, 20 met criteria for VH. These differed from cases without VH because of the predominance of medullary symptoms. In the VH cohort, 11 patients underwent surgical decompression with symptom resolution; 9 were initially managed conservatively, but 3 subsequently required surgery.

CONCLUSIONS: We define a novel Chiari entity, Chiari type 0.5 malformation, characterized by ventral tonsillar wrapping around the medulla in young children in the absence of classic Chiari type 1 malformation imaging findings. These patients are more likely to present with medullary symptoms than patients without VH. They are also more likely to require surgical decompression and respond favorably to intervention.

Alternate JournalWorld Neurosurg
PubMed ID32204296