Frequency of meningeal enhancement caused by lumbar puncture.

A recent inquiry of whether a lumbar puncture can cause meningeal enhancement led us to the paper, “Frequency of Unexplained Meningeal Enhancement in the Brain After Lumbar Puncture,” by Mittl and Yousem (1). The conclusion that intracranial dural-arachnoidal enhancement after lumbar puncture is uncommon is not supported by the data that are presented. In their prospective study, they claim the occurrence of enhancement that may have been attributable to lumbar puncture was in 1 of 97 patients. A falsely low frequency of enhancement that may be attributable to lumbar puncture was obtained because 6 and possibly many more patients with another possible cause of meningeal enhancement were included. If any of these patients had demonstrated enhancement, the enhancement would have been attributed to the other cause and not to the lumbar puncture. To find the true frequency of enhancement caused by lumbar puncture, we need to know the number of patients who had no other possible cause for meningeal enhancement. The frequency would be the number of cases with unexplained enhancement divided by the number of patients with no other possible cause for the enhancement. Additionally, given that a lumbar puncture was a possible explanation for enhancement in 2 of their 18 cases, the conclusion that lumbar puncture is an unlikely cause of intracranial meningeal enhancement is not supported. Furthermore, because the entities that were used to explain the meningeal enhancement in the other 16 cases do not produce meningeal enhancement in 100% of affected patients, the authors have not proved that lumbar puncture did not contribute to or entirely cause the meningeal enhancement in these patients. Despite our objections to the logic used in evaluating the data in this paper, we agree with the authors that meningeal enhancement after lumbar puncture should be entertained as a diagnosis only after more serious central nervous system conditions have been excluded.