Clinical Studies and Pre-clinical Animal Models on Facial Nerve Preservation, Reconstruction, and Regeneration Following Cerebellopontine Angle Tumor Surgery–A Systematic Review and Future Perspectives

Abstract

Background and purpose: Tumorous lesions developing in the cerebellopontine angle (CPA) get into close contact with the 1st (cisternal) and 2nd (meatal) intra-arachnoidal portion of the facial nerve (FN). When surgical damage occurs, commonly known reconstruction strategies are often associated with poor functional recovery. This article aims to provide a systematic overview for translational research by establishing the current evidence on available clinical studies and experimental models reporting on intracranial FN injury.Methods: A systematic literature search of several databases (PubMed, EMBASE, Medline) was performed prior to July 2020. Suitable articles were selected based on predefined eligibility criteria following the Preferred Reporting Items for Systematic Reviews and Meta Analyses (PRISMA) guidelines. Included clinical studies were reviewed and categorized according to the pathology and surgical resection strategy, and experimental studies according to the animal. For anatomical study purposes, perfusion-fixed adult New Zealand white rabbits were used for radiological high-resolution imaging and anatomical dissection of the CPA and periotic skull base.Results: One hundred forty four out of 166 included publications were clinical studies reporting on FN outcomes after CPA-tumor surgery in 19,136 patients. During CPA-tumor surgery, the specific vulnerability of the intracranial FN to stretching and compression more likely leads to neurapraxia or axonotmesis than neurotmesis. Severe FN palsy was reported in 7 to 15 % after vestibular schwannoma surgery, and 6% following the resection of CPA-meningioma. Twenty-two papers reported on experimental studies, out of which only 6 specifically used intracranial FN injury in a rodent (n = 4) or non-rodent model (n = 2). Rats and rabbits offer a feasible model for manipulation of the FN in the CPA, the latter was further confirmed in our study covering the radiological and anatomical analysis of perfusion fixed periotic bones.Conclusion: The particular anatomical and physiological features of the intracranial FN warrant a distinguishment of experimental models for intracranial FN injuries. New Zealand White rabbits might be a very cost-effective and valuable option to test new experimental approaches for intracranial FN regeneration. Flexible and bioactive biomaterials, commonly used in skull base surgery, endowed with trophic and topographical functions, should address the specific needs of intracranial FN injuries.

Nomogram for Predicting Facial Nerve Outcomes After Surgical Resection of Vestibular Schwannoma

“…It is well known that the intracranial intra-arachnoidal FN is covered by a sheath of arachnoid membrane and lacks a peri- and epineural layer ( 16 ). The risk of FN injury is high in the operation of VS because of FN particular vulnerability to stretching (lack of perineurium) and reduced resistance to compression (lack of epineurium) ( 17 ). In this study, approximately 24% of patients with surgical resection of VS had poor FN outcomes (H-B grades III–VI) at discharge.…”

Contemporary Perspectives in Pathophysiology of Facial Nerve Damage in Oto-Neurological and Skull Base Surgical Procedures: A Narrative Review

“…At the same time, in patients whose facial nerve was anatomically discontinued and reconstructed with cable graft, a House-Brackmann grade III was achieved in up to 61-70% of cases [14]. The discrepancy between anatomical and functional preservation rates has also been highlighted in the more recent literature [5,15]; it might be explained by the multiple mechanical traumas caused to the FN over its whole intracranial length during surgical dissection despite a gross anatomical preservation.…”

“…When approaching a tumor component in the cerebello-pontine angle, the root exit zone should be constantly identified by low-intensity stimulation [16], thus also gaining information on the function of the distal parts of the nerve. While debulking the tumor mass, one of the main technical issues concerns the management of mechanical stress, generated by direct and indirect tractions, while pulling the extensible cisternal part of the nerve away from its labyrinthine tract, which is constrained within its bony canal [13,15,17]. Therefore, to minimize traction on the labyrinthine tract, dissection should proceed in a medial to lateral way [1].…”

“…The FN may be flattened on the tumor surface, making it difficult to separate it from the tumor capsule, which generally occurs at the superior pole. It can also be potentially dislocated more anteriorly, or more dorsally than expected [13,15,18,19]. In such situations, a careful identification of nerve fibers, even by means of a supramaximal stimulation [16,19], should be performed to allow full anatomical preservation.…”

“…The FN shows an extension limit beyond which it cannot be stretched without causing functional damage. However, this limit is not clearly definable in clinical practice, being reported to range between 6 and 20% of nerve length, based on experimental data [15,17,31,32]. As a result, dissection maneuvers leading to nerve stretching should be limited, and care should be taken to avoid direct traction at the level of the nerve entry into the fallopian canal since the bony-coated labyrinth tract is inextensible.…”