Supracerebellar arachnoid cyst and reversible tonsillar herniation: magnetic resonance imaging and pathophysiological considerations

A large supracerebellar arachnoid cyst was associated with herniation of the cerebellar tonsils and deformity of the cervicomedullary junction in an adult. Magnetic resonance imaging showed partial restoration of normal anatomy following surgery and clinical improvement, which helped in the formulation of a etiopathogenetic hypotheses.