Facial Nerve Schwannomas Mimicking as Vestibular Schwannomas

Surgical management of intraoperatively diagnosed facial nerve schwannoma located at internal auditory canal and cerebellopontine angle - our experiences of 14 cases

BACKGROUND

Facial nerve schwannomas located at internal auditory canal and cerebellopontine angle (IAC/CPA FNS) were diagnosed intraoperatively, it poses a therapeutic dilemma to the surgeon.

OBJECTIVE

To report our experience in managing IAC/CPA FNS and to propose a treatment strategy.

METHODS

A total of 14 patients with IAC/CPA FNS who were diagnosed intraoperatively and treated by operation between 2015 and 2019 were retrospectively studied.

RESULTS

Unilateral hearing loss was the most common symptom and all these patients had normal facial nerve function preoperatively. Surgical approaches used in these patients including translabyrinthine (2 cases), retrosigmoid (RS) (11 cases), and middle cranial fossa (MCF) approach (1 case). Eight patients underwent partial resection, three patients underwent subtotal resection and three patients had complete tumor removal with facial nerve reconstruction. All partial resection patients and two patients underwent subtotal resection achieved a long-term HB grade I facial nerve function. The long-term facial nerve function of patients underwent complete resection and nerve grafting was no better than HB grade III.1 of the eight patients underwent partial resection experienced tumor regrowth during the follow-up.

CONCLUSIONS

Partial or subtotal resection for IAC/CPA FNS may provide an opportunity of retaining excellent facial nerve function. Regular postoperative imaging is helpful to monitor the recurrence.

Preoperative Differences in Intracranial Facial Versus Vestibular Schwannomas: A Four Nerve Assessment

OBJECTIVES

Assesses whether preoperative functional testing can distinguish vestibular schwannomas from facial nerve schwannomas medial to the labyrinthine segment.

STUDY DESIGN

Retrospective cohort.

METHODS

Retrospectively review surgically managed intracranial facial and vestibular schwannomas between January 2015 and December 2019 at two tertiary care centers. Patients with neurofibromatosis 2 and surgery for recurrence were excluded. Preoperative functional testing to include House-Brackmann scores, electroneuronography (ENoG), cervical vestibular evoked myogenic potentials (cVEMP), caloric testing, acoustic brainstem responses (ABRs), acoustic reflexes, and audiograms was compared between the two groups of schwannomas.

RESULTS

Twelve facial and 128 vestibular schwannomas met inclusion criteria. In only one case was a facial schwannoma diagnosed preoperatively from imaging. No statistically significant difference was found in preoperative House-Brackmann scores, ENoG, cVEMP, caloric testing, ABRs, or acoustic reflexes. Pure tone average was worse in the vestibular schwannoma group (63 dB [95% CI: 58-68 dB] vs. 46 dB [95% CI: 34-58 dB], P = .01), and the difference was more apparent in the lower frequencies. Word recognition score was better in the facial schwannoma group (66% [95% CI: 45-86%] vs. 41% [95% CI: 34-47%], P = .02).

CONCLUSION

Specialized preoperative functional evaluation of the nerves of the internal auditory canal cannot reliably predict the presence of an intracranial facial schwannoma. Hearing is better in facial schwannomas, particularly in the lower frequencies. This should raise the index of suspicion for an intracranial facial schwannoma, especially in candidates for hearing preservation vestibular schwannoma surgery.

LEVEL OF EVIDENCE

3 Laryngoscope, 131:2098-2105, 2021.

Cerebellopontine angle schwannomas arising from the intermediate nerve: a scoping review

Intermediate nerve schwannomas (INS) are extremely rare lesions in literature. They have been described mimicking facial nerve schwannomas, but not vestibular schwannomas (VS). We aimed to review the previously published cases, as well as the evidence to believe that they are far more common, though usually misdiagnosed as facial or VS. We performed a review of PubMed/Medline and Embase of "intermediate nerve schwannoma," "facial nerve schwannoma," "greater superficial petrosal nerve schwannoma," "geniculate ganglion schwannoma," and "chorda tympani schwannoma" to identify all cases of INS, following the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) statement. Furthermore, 2 cases operated at our center are shown to exemplify the proposed hypotheses. No article was excluded from review. Thirteen cases of INS, 11 cases of chorda tympani schwannoma, and 18 cases of greater superficial petrosal nerve schwannoma were found in literature. In facial nerve schwannomas, the predilection of schwannomas for sensory nerves, and the ability to preserve the motor facial nerve during tumor resection support the hypothesis of intermediate nerve as the nerve of origin. For VSs, the different arachnoidal arrangement of medial VS, the sharing of pia mater by the intermediate nerve and vestibular nerve, and the medial Obersteiner-Redlich zone of the intermediate nerve, support the hypothesis of intermediate nerve origin of some VS. The correct identification of the intermediate nerve as a nerve of origin of cerebellopontine angle schwannomas is of uttermost importance, especially when mistaken for VS, as this may account for the heterogeneity of facial and cochlear outcomes after surgery.

The Natural History of Facial Schwannomas: A Meta-Analysis of Case Series

Objective  This study is to establish predictors of facial paralysis and auditory morbidity secondary to facial schwannomas by assimilating individualized patient data from the literature. Design  A systematic review of the literature was conducted for studies regarding facial schwannomas. Studies were only included if they presented patient level data, House-Brackmann grades, and tumor location by facial nerve segment. Odds ratios (OR) were estimated using generalized linear mixed models. Main Outcome Measures  Facial weakness and hearing loss. Results  Data from 504 patients were collected from 32 studies. The geniculate ganglion was the most common facial nerve segment involved (39.3%). A greater number of facial nerve segments involved was positively associated with both facial weakness and hearing loss, whereas tumor diameter did not correlate with either morbidity. Intratemporal involvement was associated with higher odds of facial weakness (OR = 4.78, p  < 0.001), intradural involvement was negatively associated with facial weakness (OR = 0.56, p  = 0.004), and extratemporal involvement was not a predictor of facial weakness (OR = 0.68, p  = 0.27). The odds of hearing loss increased with more proximal location of the tumor (intradural: OR = 3.26, p  < 0.001; intratemporal: OR = 0.60, p  = 0.14; extratemporal: OR = 0.27, p  = 0.01). Conclusion  The most important factors associated with facial weakness and hearing loss are tumor location and the number of facial nerve segments involved. An understanding of the factors that contribute most heavily to the natural morbidity can help guide the appropriate timing and type of intervention in future cases of facial schwannoma.