Air encephalography for hydrocephalus in the era of neuroendoscopy.

INTRODUCTION: There is often uncertainty regarding the site of the cerebrospinal fluid (CSF) block in individual patients with hydrocephalus, leading to a significant failure rate for endoscopic third ventriculostomy (ETV) when performed for unconventional pathologies such as postmeningitic and posthaemorrhagic hydrocephalus. We describe the use of lumbar air encephalography (AEG) to refine the indications for ETV in such circumstances.
METHODS: Data from AEG studies used to guide indications for ETV were collected prospectively. The technique and protocol for AEG have been modified from the historical description of the procedure in the interest of safety and to minimise discomfort. In a separate evaluation, the level of the CSF block was determined by one of the authors, who was blinded to the results of the AEG, based on conventional computerised tomographic criteria. These results are compared with those obtained from the AEG.
RESULTS: Forty-five studies were performed over a 2-year period. Thirty-seven were preinterventional, the majority of which demonstrated communicating hydrocephalus. ETV performed in five cases of non-communicating hydrocephalus was successful in each. The prediction of the level of block based on CT criteria was poor.
CONCLUSION: It is often difficult to determine whether hydrocephalus is communicating or not with conventional imaging in the absence of a clearly demonstrable lesional obstruction to the CSF pathways. We have found AEG helpful in excluding patients with communicating hydrocephalus from an inappropriate ETV. On the basis of our experience, we consider the modified procedure safe as long as a strict protocol is followed.