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A rounded lesion with intermediate T1 and high T2 signal is noted in the roof of the third ventricle, just behind the foramina of Monro. The choroidal veins (draining the choroid plexus of the lateral ventricle), and the thalamostriate veins (which join on each side to form the internal cerebral veins) are seen stretched over the lesion.
Lateral ventricles are distended well above that expected for this age.
Features are characteristic of a colloid cyst.
The patient went on to have a resection.
Sections show the wall and lining of a cyst. The lining is composed of simple ciliated cuboidal epithelium in which no atypical features are seen. The wall is composed of loosely compacted
collagen. The features are of a colloid cyst. No evidence of tumour is seen.
DIAGNOSIS: Third ventricle colloid cyst.