Post-traumatic intracerebral pneumatocele: case report. Pneumocephalus occurs in 0.5 to 1.0% of head trauma, but may also occur after neurologic surgery, or as a result of eroding infection or neoplasm. The pathophysiology involves the presence of craniodural fistula allowing ingress of air. A ball-valve mechanism may allow air to enter but not exit the cranium, or CSF leak permits air entrance as fluid leaves the intracranial space. While a "succession splash" is considered diagnostic of pneumocephalus, most patients have nonspecific signs and symptoms such as headache. Therefore, a high index of suspicion in a patient with recent head trauma is necessary. The diagnosis is made radiographically by CT scan. This is generally performed to rule out intracranial hematoma or cerebral contusion in head trauma, but will reveal even very small quantities of air to the unsuspecting physician. Therapy is often noninvasive, allowing the craniodural defect to heal spontaneously. Selected situations require immediate operative repair of the fistula. 