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The approach angle to the interoptic triangle limits surgical workspace when targeting the contralateral internal carotid artery

  • Original Article - Neurosurgical Anatomy
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Abstract

Background

The interoptic triangle (IOT) offers a key access to the contralateral carotid artery’s ophthalmic segment (oICA) and its perforating branches (PB), the ophthalmic artery (OA), and the superior hypophyseal artery (SHA). It has been previously reported that the assessment of IOT’s size is relevant when attempting approaches to the contralateral oICA. However, previous studies have overseen that, since the oICA is a paramedian structure and a lateralized contralateral approach trajectory is then required, the real access to the oICA is further limited by the approach angle adopted by the surgeon with respect to the IOT’s plane. For this reason, we determined the surgical accessibility to the contralateral oICA and its branches though the IOT by characterizing the morphometry of this triangle relative to the optimal contralateral approach angle.

Methods

We defined the “relative interoptic triangle” (rIOT) as the two-dimensional projection of the IOT to the surgeon’s view, when the microscope has been positioned with a certain angle with respect to the midline to allow the maximal contralateral oICA visualization. We correlated the surface of the rIOT to the visualization of oICA, OA, SHA, and PBs on 8 cadavers and 10 clinical datasets, using for the last a 3D-virtual reality system.

Results

A larger rIOT correlated positively with the exposure of the contralateral oICA (R = 0.967, p < 0.001), OA (R = 0.92, p < 0.001), SHA (R = 0.917, p < 0.001), and the number of perforant vessels of the oICA visible (R = 0.862, p < 0.001). The exposed length of oICA, OA, SHA, and number PB observed increased as rIOT’s surface enlarged. The correlation patterns observed by virtual 3D-planning matched the anatomical findings closely.

Conclusions

The exposure of contralateral oICA, OA, SHA, and PB directly correlates to rIOT’s surface. Therefore, preoperative assessment of rIOT’s surface is helpful when considering contralateral approaches to the oICA. A virtual 3D planning tool greatly facilitates this assessment.

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Acknowledgements

We want to thank very much Mr. Thomas Bauer for assistance with drawings for the Fig. 1, which greatly improved the intended message of our manuscript.

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Authors and Affiliations

  1. Department of Neurosurgery, Mainz University Medical Center, Langenbeckstraße 1, 55131, Mainz, Germany

    Lucas Ezequiel Serrano, Eleftherios Archavlis, Eike Schwandt, Florian Ringel & Sven Rainer Kantelhardt

  2. Department of Neurosurgery, Saarland University Hospital, Kirrbergerstraße 100, 66421, Homburg, Germany

    Ali Ayyad

  3. Department of Neurosurgery, Charing Cross Hospital, Imperial College Healthcare, Fulham Palace Rd, London, W6 8RF, UK

    Amr Nimer

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  1. Lucas Ezequiel Serrano
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Correspondence to Lucas Ezequiel Serrano.

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The authors declare that they have no conflict of interest.

Ethical approval

This article does not contain any studies with human participants or animals performed by any of the authors. The cadaveric study followed all ethical and hygienic procedures ruled by the Hygiene and Health Department of our institution and current national and international standards. Ethical committee approval was not required as presented data correspond to cadaveric specimens and anonymized patient’s datasets, so that there is no risk of identification.

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Comments

The authors are to be congratulated for their meticulous work in studying the exposures that can be achieved through the interoptic triangle from the surgeons’ perspective. The study is performed on 8 cadaveric specimens as well as 10 clinical datasets using a 3D virtual reality system. The exposure of the contralateral ophthalmic segment of the carotid, the ophthalmic artery, as well as the superior hypophyseal artery is studied, evaluating the relative area exposed with a variety of surgical manipulations like ipsilateral clinoidectomy, drilling of the tuberculum or planum, and contralateral optic nerve mobilization. The study does not necessarily offer something radical, but there are subtle novelties that may make it a worthwhile addition to the literature.

Georgios A. Zenonos

Jacques J. Morcos

FL,USA

In this article, the authors describe the “relative interoptic triangle” (rIOT) and how size of the rIOT influences access to the contralateral ICA, OphA, SHA, and perforators. Eight cadavers and 10 clinical datasets using a 3D-VR system were used. The authors found that a larger rIOT correlated with greater exposure of the contralateral ICA, OphA, SHA, and perforators, which makes logical sense. This concept is demonstrated in Fig. 1, which shows how the surgical approaches alters rIOT size and, therefore, influences visualization of contralateral vascular structures. Figure 4 also demonstrates that significant anterior skull base removal and optic nerve mobilization greatly increase rIOT.

The ideal approach to proximal ICA pathology (i.e., aneurysm) is rarely, if ever, a contralateral approach. If a patient has bilateral ICA aneurysms, the side of approach is that of the more concerning aneurysm, and the look contralaterally is only to assess clip feasibility of the aneurysm to spare the patient a second craniotomy. While the rIOT is influenced by the craniotomy of choice, it also changes with each move of the microscope. Therefore, surgeons can increase or decrease visibility of contralateral lesions by changing their working angle. It is not clear how pre-operative assessment and determination of rIOT from a specific working angle would influence intra-operative decisions to look contralaterally or not. In addition, surgeons will only clip contralateral ICA aneurysms if they can safely do so and this is something that can only be determined at surgery.

Fady Charbel

Illinois, USA

This article is part of the Topical Collection on Neurosurgical Anatomy

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Serrano, L.E., Archavlis, E., Ayyad, A. et al. The approach angle to the interoptic triangle limits surgical workspace when targeting the contralateral internal carotid artery. Acta Neurochir 161, 1535–1543 (2019). https://doi.org/10.1007/s00701-019-03911-7

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