Editorial: Acoustics and hydrocephalus

Abstract

This retrospective study regarding management options in patients with hydrocephalus associated with vestibular schwannomas (VSs) comes from a center with a remarkably large surgical experience treating this tumor type.1 Their surgical technique has been exquisitely developed over many years, and is uniform among colleagues in their institution. They receive worldwide referrals and treat a greater than usual number of larger VSs. This helps to account for their significant experience with hydrocephalus in patients with this specific tumor; that is, larger tumors often present for a longer than usual period of time. Their consecutive series of 400 patients was collected over a 6-year period (an average of more than 66 cases per year). Their overall results with complete tumor removal and percentage of saved facial nerve function and preserved hearing is among the best reported in the medical literature.3 In evaluating the superb results herein reported (“The general and functional outcome of surgery showed no correlation to the presence of preoperative hydrocephalus.”), the above statements and the fact that these patients undergo operation in the semisitting position, with very experienced neuroanesthesiologists performing the anesthesia, must be taken into account. In most centers around the world, patients undergo this surgery in a supine (flat or slight reverse Trendelenberg) position, with the head turned or in a lateral position.2 Patients with hydrocephalus, even those with modestly elevated intracranial pressure (ICP), at induction of anesthesia can have their ICP severely elevated, and this may be obviated in the sitting position. Modest or marked elevation of the ICP will often make it more difficult to perform the surgical procedure safely and to accomplish the removal of the entire tumor while sparing the critical cranial nerves. My own recommendation (and I believe the procedures that are followed in most centers where patients are not operated on in the sitting position) would be as follows: 1) patients with symptomatic hydrocephalus accompanied by elevated ICP would have an external ventricular drain (EVD) placed, and when the ICP normalized in 1 or 2 days, they would be taken to surgery. The EVD would be left in place postoperatively, and then the patient would be gradually weaned from the drain. If weaning was not possible (as the authors recommend), a ventriculoperitoneal shunt would be placed. 2) Patients with asymptomatic hydrocephalus and those with normalpressure hydrocephalus (NPH) symptomatology would have an EVD placed at the beginning of anesthesia, the pressure would be kept in a normal range during the operation to mitigate elevated pressure transmission to the posterior fossa, and then after surgery the drain would be left in, and then usually removed in 1–2 days, as long as the clamped pressure permitted this. With this approach, the incidence of permanent hydrocephalus (obstructive or communicating), and CSF leakage would probably be similar to that reported herein. The authors emphasize the advantages of avoiding an EVD, but the desirability of this EVD approach in the patient who undergoes surgery in the recumbent position would be a less complex surgical procedure, with a better chance of total tumor removal, with sparing of critical cranial nerves. This is not the type of evaluation that is compatible with the design of a prospective trial. Indeed, it is a report most appropriately summarized for clinical recommendations based on clinical experience. There continues to be an important place for such published reports, and the expectation of prospective or double-blind trials in this arena is inappropriate. That is the reason my editorial contains remarks based on clinical experience, and why the recommendations the authors make based on their own observations in their own unique environment are of great value. I seriously doubt that their proposed design of a prospective trial will be successful, particularly in light of their proposal to obtain lumbar CSF to measure protein levels both before and after tumor removal: obtaining CSF in a patient with a large posterior fossa tumor remains an unquestionably dangerous procedure.