2026 Poster Presentations
P447: SURGICAL ANATOMY OF NERVUS INTERMEDIUS: OPTIMIZING ITS IDENTIFICATION AT THE BRAINSTEM FOR TREATMENT OF GENICULATE NEURALGIA AND OTHER CEREBELLOPONTINE ANGLE SURGERIES
Rosaria Abbritti, MD1,2,3; Yohan Alexander, MD1,2; Sandhya R Palit, MD1,2; Florian Moser1,2,4; Luciano CPC Leonel, PhD1,2,5; Maria Peris-Celda, MD, PhD1,2,5; 1Department of Neurologic Surgery, Mayo Clinic, Rochester, Minnesota, USA; 2Mayo Clinic Rhoton Neurosurgery and Otolaryngology Surgical Anatomy Program, Rochester, Minnesota, USA; 3Department of Neurologic Surgery, Lariboisière University Hospital, Université Paris Cité, Paris, France; 4Paracelsus Medical University, Salzburg, Austria; 5Department of Clinical Anatomy, Mayo Clinic College of Medicine and Science, Rochester, Minnesota, USA
Background: Precise prediction and identification of the nervus intermedius (NI) is critical to safely perform surgical treatment of geniculate neuralgia. It can also be identified and preserved in other surgeries such as vestibular schwannoma resection.
Objective: To analyze the microsurgical anatomy of the NI at the brainstem and its relationship to the venous complex identifying potential additional landmarks that may facilitate a reliable intraoperative identification of the nerve.
Materials and Methods: Seven formalin-fixed, latex-injected cadaveric heads (14 sides) were dissected. For illustrative purposes and to expose the lateral aspect of the brainstem, a retrosigmoid combined with posterior petrosal and translabyrinthine approaches was performed. The origin of the NI, its position relative to CNs VII and VIII at the brainstem, and its relationship to the regional venous network were systematically evaluated.
Results: The nervus intermedius (NI) was identified in all specimens. A single origin was observed in 10 sides (71.4%), whereas multiple origins were present in 4 sides (28.6%) (Fig. 1). The number of bundles ranged from 1 to 5. Among the single-origin group, in 7 sides (70%) one or more bundles arose from the vestibular nerve, whereas in 3 sides (30%) they arose directly from the brainstem. In the multiple-origin group, a total of 16 bundles were identified: 8 (50%) originated from the vestibular nerve, 1 (6.2%) from cranial nerve (CN) VII, and 7 (43.8%) from the brainstem. The position of the NI at the brainstem was consistently anterior, inferior, and medial to the vestibular nerve and superior and lateral to CN VII at their root entry zones (REZs). A consistent relationship between the tributaries of the superior petrosal vein (SPV) and the CN VII–NI–VIII complex was observed. Three main positions of the middle cerebellar peduncle (MCP) vein were identified before its drainage into the cerebellopontine fissure vein. In 3 sides (21.4%), the vein was located between CN VIII–NI complex and CN VII; in 9 sides (64.3%), it was located posterior to the CN VII–NI–VIII complex (Fig. 2); and in 2 sides (14.3%), it was located anterior. In 1 of the posteriorly configured cases (11.1%), a recurrent branch of the MCP vein projected superiorly between CN VIII–NI and CN VII. From a technical standpoint, the safest zone for identification of the NI bundles, avoiding excessive manipulation of vestibular and facial nerves, was at the REZ of the CN VII–NI–VIII complex. Following the bundles to their deepest portion allowed clear visualization of their origin and reduced the risk of fiber misinterpretation or inadvertent nerve injury. The venous pattern surrounding the CN VII–NI–VIII complex could be reliably identified at the level of the SPV.
Conclusion: The surgical anatomy of NI is intimately related to CN VII-VIII complex. Its origin is found inferomedial to the root entry zone (REZ) of the vestibular nerve and superolateral to the facial nerve.
The position of MCP vein between CN VIII-NI complex and CN VII could represent a useful and additional landmark to identify the NI at brainstem.
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