Cerebellar Tonsillar Ischemia and Cysts in the Chiari I Malformation

Rare reports in the literature have documented the presence of a cyst at the tip of the cerebellar tonsil in patients with Chiari I malformation. The authors prospectively reviewed all new Chiari I malformation (CM I) pediatric patients who presented to their clinic during a 2-year period. Specifically, all patients were screened for ischemic or cystic lesions of the herniated cerebellar tonsils on magnetic resonance imaging (MRI). Out of 340 patients, 2.9% were found to have signal changes on MRI consistent with ischemia or cysts in the cerebellar tonsils. For both ischemic and cystic cerebellar tonsils, histologically, the tissue demonstrated loss of Purkinje cells with concomitant Bergmann gliosis. Based on the findings, cerebellar tonsillar ischemia and cysts in patients with CM I can often be seen radiologically. Histologically, these ischemic and cystic tissues are the same. Taken together, cerebellar tonsillar ischemia and cysts are on a continuum and represent chronic compression of this herniated part of the cerebellum.