Pneumosinus dilatans: a discussion of four cases and the possible aetiology.

Pneumosinus dilatans is an abnormal dilatation of the paranasal sinuses, which contains only air and is lined by normal mucosa. It is a rare condition, the aetiology of which is unclear. We describe four patients who presented to our department with pneumosinus dilatans. The aetiology was either developmental hydrocephalus (n = 1), post-traumatic (n = 1) or idiopathic (n = 2). Two patients underwent surgery, and follow-up is at least 12 months to date. The radiological aspects of this rare condition and the possible aetiologies are discussed.