Suprasellar arachnoid cysts are benign developmental congenital collections of cerebrospinal fluid and constitute ~9% of all arachnoid cysts. 

This patient has no displaced floor of the third ventricle or hydrocephalus.

Neurological and ophthalmic examination and further MR-control are indicated for this situation at the current time. 

Differential diagnosis includes: cystic craniopharyngioma (adamantinomatous type - less likely due to the lack of a high protein content/machinery oil, and the absence of solid components and calcification); Rathke's cleft cyst (the majority is completely or mostly intrasellar) and neurocysticercosis (vesicular stage - no cyst with dot sign, lack of other lesions).