Pneumosinus dilatans of the sphenoid sinus.

Four cases of pneumosinus dilatans of the sphenoid sinus are reported, supplementing the eight cases previously reported in the literature. This rare entity is characterized by expansion of a paranasal sinus that contains only air. In one patient, severe visual loss due to compression of the optic canal by the adjacent enlarged sinus was seen. Galactorrhea occurred in one patient, and three of the four patients reported headaches. There was dehiscence of the sinus roof in two cases, which apparently resulted in a cerebrospinal fluid fistula in one. Previous reports of this entity are reviewed, and the radiographic findings and clinical presentations are discussed. It is proposed that the term "pneumosinus dilatans" be used to describe all dilated, air-filled sinuses with outwardly bulging walls when the primary cause is uncertain.