2026 Proffered Presentations
S073: ANATOMICAL VARIATIONS OF THE STYLOMASTOID ARTERY AND ACCESSORY FORAMINA: IMPLICATIONS FOR FACIAL NERVE PRESERVATION IN THE TRANSCOCHLEAR APPROACH
Collin Liu, MD1; Vera Vigo, MD1; Byron Hontiveros, MD1; Yuanzhi Xu, MD1; Vinay Jaikumar, MD2; Jason Davies, MD, PhD2; Alex Evins, MD, PhD3; Matei Benu, MD1; Antonio Bernardo, MD3; Spiros Blackburn, MD4; Elad Levy, MD2; Adnan Siddiqui, MD, PhD2; Juan Fernandez-Miranda, MD1; 1Stanford University; 2University at Buffalo Neurosurgery; 3Weill Cornell Medicine; 4University of Texas Health Sciences Center Houston
Introduction: Advances in endovascular and endonasal techniques have reduced the use of the transcochlear approach for ventral brainstem lesions. However, this approach remains essential for extensive glomus tumors involving the petrous temporal bone. Postoperative facial nerve (FN) palsy remains a significant complication, with reported rates by Angeli et al. up to 95% and complete paralysis in 50% of patients. This morbidity may result from injury to the arterial supply of the FN during drilling or nerve mobilization.
The fallopian canal, housing the FN, is an irregular tubular structure with small arterial apertures penetrating its walls. Understanding the arterial variants supplying the descending segment of the FN is critical for optimizing surgical preservation.
Objective: To characterize anatomical variations of the arterial supply to the descending FN segment and the presence of accessory foramina near the stylomastoid foramen (SMF) through osteological analysis, anatomical dissection, and clinical imaging.
Methods: Fifty-three dry skulls (106 sides) were examined for accessory foramina adjacent to the SMF. Seven latex-injected cadaveric specimens underwent dissection using a standard translabyrinthine approach, with meticulous preservation of arterial feeders to the fallopian canal.
Clinically, one patient with a posterior fossa hemangioblastoma underwent selective external carotid artery (ECA) injection using Siemens ARTIS Icono biplane Micro-DynaCT angiography to visualize fine microvasculature supplying the FN and tumor region.
Results:
Osteological Analysis: Accessory foramina were identified in 34% (36/106) of sides. Most were located anteromedial to the SMF (72.2%, 26/36), with 11% (4/36) directly medial (Figure 1). Some SMFs displayed compartmentalization, suggesting separate bony channels for the FN and vascular structures.
Cadaveric Dissection: The stylomastoid artery (SMA) entered the fallopian canal either directly through the SMF – Type A-, medial to the FN (Figure 2A); through a separate accessory foramen -Type B- (Figure 2B); or via both routes simultaneously -Type C-, with branches entering through distinct canals (Figure 2C). The SMA most commonly originates from the posterior auricular artery, but also arises from the occipital or ascending pharyngeal arteries.
Clinical Correlation: Preoperative Micro-DynaCT angiography confirmed an artery entering an accessory foramen separate from the SMF, penetrating the fallopian canal to supply the FN (Figure 3).
Conclusion: The vascular supply to the descending FN segment is highly variable and frequently courses through separate bony canals near the SMF. These variants pose a risk of inadvertent arterial injury during transcochlear or facial nerve transposition procedures, potentially contributing to high postoperative FN palsy rates. Preoperative vascular mapping with Micro-DynaCT angiography may enhance surgical planning and facilitate preservation of FN function. Further anatomical studies are warranted to refine strategies for safe nerve mobilization and minimize morbidity.
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