Pilocytic Astrocytoma of Fornix Mimicking a Colloid Cyst: Report of 2 Cases and Review of the Literature.

BACKGROUND: Colloid cyst is a gelatin-containing cyst in the brain almost always found in the third ventricle. The specific shape and location of these cysts, a round well-delineated mass in the rostral part of the third ventricle adjacent to the foramen of Monro, on imaging are the main findings for diagnosis. Several masses of the third ventricle masquerading colloid cysts on images have been reported. Based on different surgical approaches, preoperative misdiagnosis of colloid cyst may have great impact on prognosis.

METHODS: We report 2 cases that presented with severe headache and hydrocephalus, and their preoperative images were highly indicative of colloid cyst.

RESULTS: Histopathologic investigations after tumor resection showed pilocytic astrocytoma of fornix in both cases.

CONCLUSIONS: Fifteen cases of colloid cyst misdiagnosis with other masses have been reported thus far; among them, 2 cases were pilocytic astrocytoma. In this study we report 2 other cases. Furthermore, we discuss additional clues helping to differentiate pilocytic astrocytoma from colloid cyst on images.