The incidence, volume, absorption, and timing of supratentorial pneumocephalus during posterior fossa neurosurgery conducted in the sitting position.

BACKGROUND: Supratentorial pneumocephalus (STP) is a known complication of neurosurgical procedures of the posterior fossa when conducted in the sitting position. Few studies have examined STP as differentiated from pneumocephalus in the operative field.
METHODS: Ninety-five of 106 consecutive patients had postoperative radiographic studies and median nerve somatosensory evoked potential (SSEP) recording during surgery. STP was identified on postoperative skull films or computerized tomography (CT). STP volume was measured on CT scans. SSEP changes were identified in the monitoring records.
RESULTS: STP was identified in 40 patients (42.1%). STP volume on CT scans within 4 hours of surgery ranged from 6 to 280 cm3 (cubic centimeters). An extraventricular drain or ventriculo-peritoneal shunt did not increase the incidence of STP (P=0.85). The absorption of STP in 5 patients with multiple CT scans showed an immediate reduction of 24% followed by exponential decay with an half life of 1.5 days. Four patients with an extraventricular drain or ventriculo-peritoneal shunt had excessive volume of STP when measured at 1 day or later. Six patients with significant SSEP amplitude reductions attributed to STP had volumes exceeding 90 cm3 on a CT scan within 4 hours of surgery. The onset of these changes occurred at various times from dural opening to closing.
CONCLUSIONS: STP is common after posterior fossa neurosurgical procedures conducted in the sitting position. Further studies are needed to fully characterize the absorption of air and the timing of the entry.