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S234: MICROVASCULATURE OF CNS VII AND VIII AT THE BRAINSTEM AND THE MIDDLE CEREBELLAR PEDUNCLE: SURGICAL ANATOMY AND CLINICAL RELEVANCE
A. Yohan Alexander, BA^1,2,3; Rosaria V Abbritti, MD^1,2,4; Luciano Leonel^1,2,5; MIchael J Link, MD^1,2,6; Maria Peris-Celda, MD, PhD^1,2,5,6; ¹Rhoton Neurosurgery and Otolaryngology Surgical Anatomy Program, Mayo Clinic, Rochester, MN; ²Department of Neurologic Surgery, Mayo Clinic, Rochester, MN, USA; ³Medical School, University of Minnesota, Minneapolis, MN, USA; ⁴Department of Neurosurgery, Lariboisière Hospital, Assistance Publique - Hôpitaux de Paris, Paris, France; ⁵Department of Clinical Anatomy, Mayo Clinic, Rochester, MN, USA; ⁶Department of Otorhinolaryngology, Mayo Clinic, Rochester, MN, USA

Introduction: Posterior fossa neurovascular anatomy is well described. No study to our knowledge, however, focuses on microvascular anatomy at the region of cranial nerves (CNs) VII and VIII at the brainstem and the middle cerebellar peduncle (MCP). As such, in this study we detail the microvascular anatomy of this region and discuss its clinical implications.

Methods: On 12 sides of six embalmed, latex-injected specimens, retrosigmoid approaches in combination with translabyrinthine drilling and division of the sigmoid sinus was performed to afford an optimal view of the lateral pons and pontomedullary junction. For venous anatomy, the vein of the MCP was studied. Specifically, if present, we looked at its drainage location, relationship to CNs VII and VIII, and described any branches. For arterial anatomy, we identified the perforators supplying the MCP, the root exit zone of CN VII, and root entry zone of CN VIII. We quantified how many perforators each structure received and identified the segment of the artery from which they arose. Clinical implications of our findings are discussed.  

Results: Regarding venous anatomy, the vein of the MCP was present in 12 sides (100%). It was consistently identified as the inferior most tributary of the superior petrosal venous complex. With reference to the CNs VII and VIII bundle, it ran posterior to the bundle in 7 sides (58.3%), anterior to the bundle in 3 sides (25%), and between the bundle in 2 sides (16%). The vein of the MCP consistently ran inferiorly to connect with the vein of the pontomedullary sulcus. A small vein branching from the vein of the MCP and splitting the CNs VII and VIII bundle at the brainstem was identified in 10 sides (83.3%). The only specimens in which this small vein was not present were those in which the vein of the MCP was already between the CN VII and CN VIII bundle. Regarding arterial perforators, the median number of perforators to the root exit zone of CN VII was 1 (range:0-4). Sixty percent of these perforators arose from the pre-meatal segment of the anterior inferior cerebellar artery’s (AICA’s) A2 segment. The median number of perforators to the root entry zone of CN VIII was 1 (range:0-4). Fourty percent of these perforators arose from the pre-meatal segment of AICA’s A2 segment and 20% arose from the labyrinthine artery. The median number of perforators to the MCP was 2 (range:1-6). Sixty-eight percent of these perforators arose from the post-meatal segment of AICA’s A2 segment or its A3 segment. One perforator to the MCP arose from the basilar and S4 segment of the superior cerebellar arteries each.

Conclusion: We demonstrate that the vein of the MCP serves as an excellent landmark to identify CNs VII and VIII at the brainstem and can consistently be identified by following the tributaries of the superior petrosal vein inferiorly. We also elucidate that, at the brainstem, CNs VII and VIII are supplied by the perforators arising from the pre-meatal AICA. The perforators arising from the post-meatal AICA supply the MCP. 

 

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