Outcome of Oculomotor Nerve Palsy from Posterior Communicating Artery Aneurysms

In Reply: We appreciate Dr. Choudhari's Letter to Editor regarding our article, “Outcome of Oculomotor Nerve Palsy from Posterior Communicating Artery Aneurysms: Comparison of Clipping and Coiling” (1). We did not elaborate on possible mechanisms underlying oculomotor nerve palsy (ONP) for two reasons. First, the study was retrospective, and the available data were insufficient to perform such an analysis. Second, the purpose of the study was to compare the efficacy of surgical and endovascular treatment based only on the manifestation of ONP caused by a posterior communicating artery (PComA) aneurysm. We agree that there are several possible mechanisms (i.e., direct compression, pulsating/throbbing effect, or an “irritating” effect). However, only direct compression has been observed intraoperatively by previous authors and us. A PComA aneurysm need not be large to compress the oculomotor nerve given the proximity between the PComA and the oculomotor nerve (2). The most important factor is the direction in which the aneurysm projects in relationship to the oculomotor nerve. Inferiorly and laterally projecting aneurysms more likely compress the nerve (2). Angiography often shows a notch at the inferior and lateral part of a PComA aneurysm dome (Fig. C2). Presumably, the notch indicates the site of oculomotor compression. Intuitively, this type of ONP will likely benefit by surgical clipping of the aneurysm. In contrast, the presence of densely packed coils could, in theory, be detrimental to the nerve by causing further compression. In our series, ONP resolved in two patients in the coiling group. However, it was less often seen in the patients with coiling compared with patients who underwent surgical treatment (1). In patients who recover after coil embolization, ONP has been attributed to the pulsating, throbbing, or irritation effect of the aneurysm. Our data, however, were unable to determine the mechanisms. Perhaps, it is impossible to identify the mechanisms of ONP with current technology.FIGURE. C2: Two-dimensional anteroposterior and lateral (A), and three-dimensional lateral (B) views of three cerebral angiograms from three cases of ONP. The common feature is the inferolateral “notch” on the aneurysm dome, presumably indicating direct compression on the ipsilateral oculomotor nerve.We are glad that the authors' experience concurs with our results. We agree that it will be ideal in choosing treatment modalities for different subgroups of patients if the mechanism of ONP in the presence of a PComA or other aneurysms can be identified and analyzed. Although it is unlikely that all mechanisms will be elucidated, a well-designed randomized multicenter trial might identify the best treatment modalities. P. Roc Chen Sepi Amin-Hanjani Felipe C. Albuquerque Cameron G. McDougall Joseph M. Zabramski Robert F. Spetzler Phoenix, Arizona