Spontaneous intracerebral pneumocephalus after ventriculoperitoneal shunting in patients with posterior fossa tumors: report of two cases.

Two cases of pneumocephalus after ventriculoperitoneal shunt placement in patients with posterior fossa tumors were reported. In each instance, air entered the ventricles through a porencephalic cavity in the temporal lobe that communicated with the mastoid air cells. Thinning of the petrous bone may occur secondary to chronic hydrocephalus or congenital factors. The decrease of intracranial pressure after a shunt might play a role in causing pneumocephalus. The early discovery of the site of air entrance by computed tomographic scan and the direct repair of the bone and dural defect should be mandatory.