Pneumoencephaly following lumbar puncture in association with an ethmoidal osteoma and porencephalic cyst.

A 50-year-old woman developed pneumoencephaly following a CSF examination for evaluation of dysequilibrium. Previous investigations had demonstrated a number of high signal T2 lesions on MRI of the brain. In addition, there was what was thought to be an asymptomatic cystic lesion in the left frontal lobe communicating with the lateral ventricle. After the lumbar puncture she developed extensive pneumoencephaly with pressure dilatation of the ventricular system. There was CSF rhinorrhoea. Further CT scans showed an osteoma in the ethmoidal air sinus with protrusion into the cystic area. This was the site of both the CSF leak and air entry. Caution must be taken when considering a CSF examination in the presence of either a presumed asymptomatic porencephalic cyst or ethmoid osteoma.