Although nearly half of all schwannomas involve the head and neck region, nasal and paranasal sinus presentations are quite rarely seen. Cystic schwannoma, characterized by cyst formation lined by S-100 protein positive membrane-like structures is very uncommonly seen in sphenoid sinus with only a single previously reported case. Here we report a young patient of cystic schwannoma of the paranasal sinuses having epicenter in the sphenoid sinus. The tumor had caused extensive erosion of the skull base and paranasal sinuses and extended intracranially that radiologically mimicked as infected mucocele causing loss of vision. This case denotes the aggressive behavior of such uncommon tumors.