Spontaneous pneumocephalus.

Pneumocephalus (PC) is defined as an intracranial gas collection. The majority of cases of PC are secondary to trauma or are iatrogenic. Spontaneous, non-traumatic PC is an uncommon condition. Most cases of spontaneous PC occur in association with infection, neoplasia or disease of otogenic origin. The case of spontaneous PC being presented was felt to have resulted from air being forced into a small deficit in the posterior wall of the sphenoid sinus following an episode of nose blowing.