[Tension pneumocephalus. A frequently misconstrued complication following neurosurgical operations].

Two cases of pneumocephalus are presented, complicating posterior fossa surgery in the sitting position and following craniotomy in the supine position. Intraoperative loss of cerebrospinal fluid, reduced cerebral volume and unnatural communications like fistulas and cerebrospinal fluid drainage are predisposing factors. Time and nitrous oxide tension affect the formation of the subdural air collection and its clinical symptoms, which are marked by a delay in the expected return to consciousness after operation or by postoperative deterioration of the neurosurgical status. CT scan or lateral skull X-ray lead to prompt diagnosis. Use of nitrous oxide is contraindicated in anaesthesia for surgical relief of tension pneumocephalus.