Primary tumors and other masses of the cerebellum and fourth ventricle: Differential diagnosis by computed tomography

Summary

Seventy-three tumors of the cerebellum and fourth ventricle were analyzed by computed tomography to establish criteria for identifying the location and histology of the tumor. Brain stem tumors and metastases were excluded from the study. Tumors within the fourth ventricle are usually central in location, have a lucent halo and show no evidence of a separate, displaced fourth ventricle. Tumors within the cerebellar hemispheres are usually eccentric in location, lack a halo and displace the fourth ventricle. Ependymomas may be distinguished from classical medulloblastomas because they calcify more frequently, have small lucent zones, and extend into the cisterns of the cerebellopontine angles. Hemangioblastomas may be distinguished from cerebellar astrocytomas because they are usually not calcified, are smaller than astrocytomas and often exhibit central necrosis of smaller tumors than astrocytomas. In many cases, cerebellar sarcomas (desmoplastic medulloblastomas) may be distinguished from astrocytomas by their homogeneously increased attenuation homogeneous contrast enhancement and lack of calcification. In this series, all intraventricular lesions with ring blushes after contrast enhancement, and all but one intraventricular lesion with well defined lucencies, were ependymomas. All calcified extraventricular lesions were astrocytomas. No medulloblastoma, ependymoma or cerebellar sarcoma demonstrated homogeneously decreased attenuation and none was a predominantly cystic mass. The criteria presented tend to localize and identify accurately the vast majority of intraventricular and hemispheric masses, in the posterior fossa.