Pneumosinus dilatans and arachnoid cyst: a unique association.

A 35-year-old female nurse presented with an 8-month history of headaches often precipitated by valsalva type maneuvers. The patient occasionally experienced tingling in her face and left arm associated with several episodes of blurred vision. The neurologic exam was normal as was the electroencephalogram. Plain skull films showed asymmetric pneumatization of sphenoid sinus (Fig. 1A). Computed tomography (CT) scan in the axial plane showed a large extra-axial lesion of the left hemisphere (Fig. 1 B) showing mass effect. Magnetic resonance (MR) imaging in the coronal imaging plane at Tl -weighting (800/20/1) showed a large arachnoid cyst of the left anterior and middle cranial fossa and ballooning of the adjacent sphenoid sinus into the lesion (Fig. 1 C). A far smaller arachnoid cyst of the right temporal lobe tip was also noted. An arachnoid cyst of the left hemisphere was confirmed surgically at the time of placement of cystoperitoneal shunt.