MR and CT of masses of the anterosuperior third ventricle.

Six patients with masses of the anterosuperior portion of the third ventricle were imaged with MR and CT. Four patients had proved colloid cysts, one patient had a proved astrocytoma, and one patient had a presumed colloid cyst. Multiplanar MR imaging provided accurate localization of the anterosuperior third-ventricle mass in all cases. The MR intensity characteristics of the colloid cysts varied and the astrocytoma could not be differentiated from the colloid cysts on MR. The astrocytoma contained a calcification that was clearly demonstrated on CT but was difficult to appreciate on MR. Neither MR nor CT was useful in predicting success of stereotactic aspiration of the colloid cysts in this small series, but the presence of thin, low-viscosity cyst contents could be suggested by both examinations.