In Reply

We thank Kurbanov et al for their comments on our recent article.1 Their analogy to the Tower of Babel is yet another attestation to their sophistication not only in neurosurgical anatomy but also in theology and philosophy. The purpose of the internal carotid artery (ICA) road map is to provide endoscopic skull base surgeons, regardless of their native specialty, a simple, practical, and comprehensive classification of the ICA segments as viewed from a ventral cranial perspective. Furthermore, the road map outlines numerous surgical landmarks that can be used to identify the ICA before meeting it inadvertently. Finally, the new classification constitutes a foundation for an easy categorization of endoscopic endonasal surgical approaches to the skull base. Faced with the need for a common language that allows clear and practical communication between surgical teams intraoperatively and in scientific discourses, one has to choose between 1 of 2 philosophical approaches: approach 1, design a new classification tailored to specifically address and categorize the endoscopic endonasal surgical modules; or approach 2, modify an already existing classification by adjusting the nomenclature and forcing it on the endoscopic endonasal surgical modules. We have decided to use the former approach for the following reasons: 1) In a specialty that brings neurosurgeons and otolaryngologists to the same team, it is important to use a system that satisfies the needs of both fields. Some of the nomenclature we used (eg, paraclival and parapharyngeal) has been present in the otolaryngology and skull base literature for a very long time and has proven easy to use because it represents descriptive regions. 2) In our experience in teaching expanded endoscopic courses over the last decade, we have noticed that trainees find it easier to communicate nomenclature that is based on osseous anatomy (eg, sella, clivus, clinoid) rather than loops and bends. 3) Even with the exchange of loops for bends in the Bouthillier classification system, we feel that the scheme is not adequate to form a basis for classifying the current endoscopic endonasal approaches. We most certainly recognize the density and intensity of the ICA road map article, and we can understand why Kurbanov et al might have felt that some facts were misleading from their perspective. We would like to clarify the 3 issues that they highlighted. First, regarding the segment of the ICA starting at the carotid bifurcation and extending to the external orifice of the ICA canal, we agree with Kurbanov et al that only the distal part of it resides in the parapharyngeal space. Nonetheless, the whole segment is related to the pharynx (hence, the descriptive term parapharyngeal applies), which extends from the skull base superiorly to the cricoid cartilage inferiorly (around the C6 body). Furthermore, in our classification, which is geared primarily toward endoscopic skull base approaches, we used the term parapharyngeal ICA for this segment to highlight the importance of the distal portion because it is the most relevant one to the endoscopic surgeon. Second, it is important to differentiate between the terms anatomic boundary and surgical landmark (Table 1 in our article). The anatomic borders/boundaries need not be identified for each segment intraoperatively (hence, they can be behind the vessel or hidden by it) because they are intended to define the relevant regional anatomy per segment to orient the surgeon. The borders are used to define the ICA segments in such a way that would help choose and design the modular surgical approaches that we have previously described. In contrast, the surgical landmarks are used to identify the ICA segments intraoperatively before meeting the vessel to execute the desired approach safely. For example, defining the upper edge of the petroclival fissure/medial petrous apex is not a necessary first step while resecting a petroclival meningioma off the paraclival/parasellar ICA. Instead, one must find as many preserved landmarks as possible (in this case, the ICA sock, the paraclival protuberance, and foramen rotunda) to identify the paraclival ICA and to follow it distally. This distinction between boundaries and landmarks is not unique to endoscopy or to our classification. Most neurosurgeons would use the sphenoid ridge or the anterior clinoid process as a landmark for identifying the paraclinoid ICA (C6 in the Bouthellier classification) when approached from a frontolateral transcranial approach as opposed to using one of its boundaries such as the proximal or distal dural rings because those rings are hidden by the vessel when approaching them laterally. Third, the road map classification system has intentionally avoided subdividing the intradural segment into further subsegments for the following reasons. The first reason is the lack of sufficient relevance to endoscopic skull base surgery; in our experience, the aneurysms alluded to by Kurbanov et al would not have been treated endoscopically in the presence of viable endovascular and time-tested open transcranial approaches. Second, the ICA road map classification, as the title of our publication explicitly indicates, is dedicated to understanding the extradural segments of the vessel as it relates to endoscopic approaches to the ventral cranial base. Nowhere do we suggest that it is intended to be a substitute for other dorsal transcranial schemes that address the intradural segments of the ICA in significant detail. It should be noted that this work is the culmination of almost 2 decades of endonasal surgery for the senior authors and represents the practical distillation of this experience to provide real-time, meaningful surgical landmarks. Every segment described in this article has been accessed effectively through the use of the representative landmark in an actual patient during surgery. Thus, this work is presented to others to replicate these approaches without having to redefine these landmarks. Disclosures Dr Kassam is a cofounder of Synaptive Medical and Regenerative Cell Sciences. He also chairs the Scientific Advisory Board for NICO Corp. He holds equity stakes in NICO Corp and Synaptive Medical and Regenerative Cell Sciences. Dr Kassam also received royalties from KLS Martin. The other authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article.

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