How Mini Can Minipterional Craniotomies Get?

Abstract

To the Editor: In their recent article, Caplan et al1 revisit the minipterional approach to aneurysms of the anterior circulation as an acceptable alternative to the traditional pterional craniotomy standardized by Yasargil.2,3 This report is yet another illustration of the current effort in aneurysm microsurgery to adopt a minimally invasive stance.4-7 However, although intuitively plausible, it is not yet clear whether minicraniotomies truly do lead to better results; too small might in fact lead to worse outcomes, related to potential intraoperative difficulties due to an inadequate exposure and the need for greater tissue retraction. The authors point out that a new approach should not sacrifice surgical efficacy for shorter hospital stays (which might in fact be longer than usual if approach-related complications occur) or for the sake of cosmetics. In other words, a novel approach has to, at least, meet the same previously achieved results. This consideration implies that the identification of the core elements for aneurysm clipping is required, and that a surgical approach be strictly limited to these for it to be truly minimally invasive.4 We see these core elements as the following: the surgeon's experience; the aneurysm's angio-architecture and that of neighboring vessels; the surgeon's representation of the angio-architecture8 and of the patient's anatomy; and surgical instruments. Cadaver studies and virtual reality laboratories remain interesting methods of exploring these issues, but they are performed “out of the operating theater.” Once in the operating room again, each new patient, bearing a different aneurysm conformation, represents a unique new challenge. Our recently reported experience with a neuronavigated augmented-reality-based setup, allowing image injection into the microscope's eyepiece to guide aneurysm clipping,9intraoperatively addresses the above-mentioned issues for each individual patient. The skin incision and craniotomy are tailored to the injected images of the patient's aneurysm, of the bony anatomy, and of the sylvian fissure; this information allows anticipating on the required work space and the best route of dissection by taking into account the given patient's anatomic particularities. For the sake of clarity, we included in our report9 illustrations of some of our earlier cases where exposition was wider. However, as our confidence in the setup grew, the performed incisions and craniotomies became smaller, as illustrated in the Figure.FIGURE: Forty-six-year-old female patient who underwent clipping of an unruptured right middle cerebral artery bifurcation aneurysm. The craniotomy was tailored to the injected images, into the operating microscope's eyepiece, of the sylvian fissure and of the segmented aneurysm (A), indicating the location of the underlying real-world aneurysm. B, after aneurysm clipping and aneurysm dome electrocoagulation. Note that the craniotomy is perfectly centered on the anterior sylvian fissure. C, demonstration of the minimal extent of arachnoid dissection, once again guided by image injection. D, 3-dimensional reconstruction of the skull from CT, illustrating the small size of minipterional craniotomies with the use of this technique; diameter of the craniotomy, 2.7 cm. E, postoperative photograph of the surgical wound. A temporal interfascial dissection is usually performed to avoid lesion to the facial nerve.Although Caplan et al do not report on the average size of the craniotomies they performed, information gleaned from their Figure indicates that it is 5 × 3.5 cm. The diameter of the craniotomy in the present figure here, showing a customized augmented reality-guided craniotomy, is 2.7 cm, corresponding to the diameter of an enlarged burr hole. In fact, we found that, when using augmented reality during the surgery of unruptured aneurysms, the main limiting factor to performing even smaller craniotomies was the relative bulkiness of the clip applier. We therefore opted for a clip applier with an inner opening mechanism (Peter Lazic GmbH, Mikrochirurgische Instrumente; Tuttlingen, Germany), instead of the traditional models where the jaws of the clip applier encompass the clip from the outside, so as to gain on space. Furthermore, we usually refrain from using self-retaining retractors. As also reported, postoperative outcome in our patients is similar, and, in any case, not worse than that of patients before we started using augmented reality.9 Finally, as stated by Caplan et al, patient selection for minipterional craniotomies is essential, and patients with ruptured aneurysms are obviously unfavorable candidates. In line with considerations from Davies and Lawton,4 craniotomy size should no longer be standardized but rather tailored to the individual patient's needs and anatomy, as well as to the surgeon's experience and the instruments at hand. Minipterional craniotomies can therefore vary in size and shape and location. In our experience, the augmented reality-based setup that we reported on can greatly help in planning and performing individualized approaches, no more and no less than what is actually needed, which is in fact the underlying definition of minimal invasiveness. Disclosure The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article.