Sonographic diagnosis of ascending transtentorial herniation of posterior fossa cystic masses.

In recent years, neonatal cranial sonography has been extensively used to diagnose intracranial hemorrhages, congenital anomalies, and intracranial masses despite such limiting factors as the size of the anterior fontanelle and lack of contrast enhancement similar to cranial CT [1] . While cranial CT during infancy lacks easy access to direct sagittal scanning, sonography offers multiplanar imaging capability. We have recently made use of cranial 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 level of 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.