Differential diagnosis of intracranial cystic lesions at head US: Correlation with CT and MR imaging

The differential diagnosis of intracranial cystic lesions at head ultra-sonography (US) includes a broad spectrum of conditions: (a) normal variants, (b) developmental cystic lesions, (c) cysts due to perinatal injury, (d) vascular cystlike structures, (e) hemorrhagic cysts, and (f) infectious cysts. These lesions vary in prevalence from common (cavum of the septum pellucidum, subependymal cyst, choroid plexus cyst) to rare (vein of Galen malformation). US can provide important information about the anatomic location, size, and shape of the lesions as well as their mass effect on adjacent structures. Differential diagnosis may be difficult because there is substantial overlap of US features between many of these conditions. However, if careful attention is paid to the location and characteristics of the cyst, a more specific diagnosis may be suggested. Understanding the spectrum of appearances of the various intracranial cystic lesions at head US improves the diagnostic yield, enables one to understand their pathogenesis, and facilitates patient care.