Arachnoid cyst - Galassi type III
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Large left frontotemporal extra-axial cystic lesion measuring 8.4 x 6.6 cm in the left middle cranial fossa, which is lined by normal grey matter, favoring the diagnosis of arachnoid cyst than porencephalic cyst. It shows CSF signal intensity in all pulse sequences and no solid components.
There is displacement of the adjacent cerebral (frontal and temporal lobes) parenchyma due to its large size, with no evidence of any perilesional edematous changes.
Widening of the sella turcica. Subtle midline shift along the anterior aspect of the falx cerebri.
One important differential is epidermoid cyst, which shows restricted diffusion and won't be completely suppressed on FLAIR images. Epidermoid cyst usually encases the vessels and neural structures.