Macro cisterna magna: a marker for maldevelopment of the brain?

Enlargement of the cisterna magna occurs in as many as 0.4% of reported patients and generally has been believed to represent a normal variant. Differentiation from Dandy-Walker malformations and other cystic structures has been emphasized. We reviewed 1,260 consecutive computed tomography reports in patients younger than 21 years of age and examined all scans in which enlargement of the cisterna magna was considered an isolated finding. Fourteen patients were identified (incidence: 1%). The primary reasons for obtaining computed tomographic scans included various clinical conditions but excluded symptoms indicative of posterior fossa disease. Developmental or neurologic abnormalities were present in 62% of these patients. Macro cisterna magna should not be dismissed as a normal variant, although the neurologic findings may not be specifically localized to the posterior fossa. This finding may be a marker for abnormal brain function most likely due to subtle disturbances in brain development.