Sonographic diagnosis of ascending transtentorial herniation of posterior fossa cystic masses

We have recently made use of caranial sonography to diagnose ascending transtentorial herniation of cystic masses of the posterior cranial fossa (cerebellar cyst and encysted fourth ventricle) in two infants. Sonographic features of ascending herniation noted on both our patients included identification of a portion of cystic mass above the tentorium and a waistlike narrowing of the mass at the levelof the tentorial notch. Early identification of ascending herniation using these criteria could prevent many potentially serious neurologic complications caused by compression of vital structures around the tentorial incisura.