Editorial

Abstract

Determining the incidence of intracerebral hemorrhagic complications caused by functional neurosurgical procedures—and what should be done to avoid them—has proven to be a controversial issue since the early days of stereotaxy. Most surgeons performing modern functional neurosurgery would probably agree, thankfully, that hemorrhages are rare events. Nevertheless, the real potential for these uncommon occurrences to produce devastating neurological morbidity or death in patients with degenerative but otherwise nonlethal conditions, rightly continues to be a source of concern. In their study, “Reducing hemorrhagic complications in functional neurosurgery: a large case series and systematic literature review,” Zrinzo et al.1 bring their considerable institutional experience to bear on the issue. The study consists of 2 parts. In the first, the authors report on the incidence of hemorrhagic complications in their own consecutive series of 214 patients they have treated with “image-guided ” implantation of deep brain stimulation (DBS) systems since 2002. Secondly, they perform a “systematic review” of series published over the past decade—including both DBS and lesioning procedures—to compute a literature-wide incidence of hemorrhage in modern functional neurosurgery and to address the relative contribution to hemorrhagic risk of several clinical and surgical factors. Ultimately, they find that the incidence of hemorrhage following functional neurosurgical interventions is about 5%, with symptomatic or permanently disabling hemorrhages being even less likely (2.1% and 1.1%, respectively). Hypertension and increasing age appear to be the most significant patient-related risk factors. The authors also conclude that using microelectrode recording (MER) or transgressing either sulci or the ventricles during surgery may increase the risk of hemorrhage and can be avoided by adopting an “image-guided” technique such as theirs. Zrinzo et al.1 are to be congratulated for the record of safety they have achieved over the past decade at their institution during surgery for DBS. As they point out, their hemorrhage rate of 0.9% per patient is among the lowest reported to date. They should also be commended for attempting to sort through the substantial literature related to hemorrhage risk in functional neurosurgery, which consists almost entirely of retrospective series of variable size and quality. Tabulating these individual series in a single paper provides a useful resource for functional neurosurgeons. Furthermore, their division of risk factors for hemorrhage into patient-related and surgical categories is a logical approach that authors of future studies would be wise to adopt. As they point out, their study does have a number of important limitations. Among others, publication bias, noncontemporaneous series, varying levels of expertise of the treating center, the learning curve across centers, differences in patient selection, and the omission of data on long-term efficacy and nonhemorrhagic side effects limit the conclusions that can be drawn from this kind of analysis. Perhaps the most salient is that in a retrospective review of the literature all kinds of observations can be made but their significance can be sometimes rather dubious. Specific findings can be associative rather than causal. As a famous example, 99% of patients with cancer have eaten pickles, but not too many would go as far as to say that this is the cause of their cancer. Similarly, the observation that there are more reports of patients with some intrinsic or extrinsic attribute (for example, pickle eaters) who have had a particular negative outcome such as hemorrhage does not prove causation. No doubt the meticulous use of MR imaging–based planning as Zrinzo et al.1 advocate has the potential to reduce the number of passes made into the brain by surgical instruments, theoretically providing less occasion to induce hemorrhage. But this theoretical advantage may be offset by the need to reposition suboptimally placed electrodes or by diminished therapeutic efficacy, which is why physiological targeting using MER remains so widespread even in this era of rapid improvements in imaging quality. Functional neurosurgery is still waiting for an unbiased, methodologically sound study that establishes the superiority of one approach over the other. Unfortunately, it is unlikely that a randomized controlled trial designed to ascertain the true hemorrhage risk conferred by various clinical and surgical factors will ever be undertaken; any such trial is doomed to be underpowered because hemorrhage is such a rare outcome and open to criticism because surgical methods are far from standardized across functional neurosurgery centers. As a result, all we can really say is that Zrinzo and colleagues have made a good attempt to address this issue, that their particular brand of “image-guided” approach to DBS surgery works well for them, and that the debate goes on.