Infrared videoangiographic assessment of cochlear nerve vasculature during middle fossa surgery

Monitoring Cochlear Nerve Action Potential for Hearing Preservation in Medium/Large Vestibular Schwannoma Surgery: Tips and Pitfalls

The diagnosis of large vestibular schwannomas (VS) with retained useful hearing has become increasingly common. Preservation of facial nerve (FN) function has improved using intraoperative EMG monitoring, hearing preservation remains challenging, with the recent use of cochlear nerve action potential (CNAP) monitoring. This prospective longitudinal series of VS with useful hearing operated on using a retrosigmoid approach included 37 patients with a mean largest extrameatal VS. diameter of 25 ± 8.7 mm (81% of Koos stage 4). CNAP was detected in 51% of patients, while auditory brainstem responses (ABR) were present in 22%. Patients were divided into two groups based on the initial intraoperative CNAP status, whether it was present or absent. FN function was preserved (grade I-II) in 95% of cases at 6 months. Serviceable hearing (class A + B) was preserved in 16% of the cases, while 27% retained hearing with intelligibility (class A-C). Hearing with intelligibility (class A-C) was preserved in 42% of cases when CNAP could be monitored in the early stages of VS resection versus 11% when it was initially absent. Changes in both the approach to the cochlear nerve and VS resection are mandatory in preserving CNAP and improve the rate of hearing preservation.

Preoperative Assessment of Cervical Vestibular Evoked Myogenic Potentials (cVEMPs) Help in Predicting Hearing Preservation After Removal of Vestibular Schwannomas Through a Middle Fossa Craniotomy

OBJECTIVE

To determine whether cervical vestibular evoked myogenic potentials (cVEMPs) are predictive of hearing preservation in patients undergoing vestibular schwannoma removal through middle fossa craniotomy approach.

STUDY DESIGN

Retrospective case study.

SETTING

Tertiary referral center.

PATIENTS

Eighteen patients who underwent a middle fossa craniotomy for vestibular schwannoma (stage I or II of Koos classification) with attempted hearing preservation from January 2008 to February 2016 were retrospectively reviewed.

INTERVENTION

Pre-surgical cVEMPs test, videonystagmography (caloric test), and magnetic resonance imaging (MRI) as well as a pre- and post-surgical audiometry test.

MAIN OUTCOME MEASURES

cVEMPs parameters including amplitude asymmetry ratio (AR), P13, and N23 latencies and peak-to-peak amplitude between P13 and N23 waves were calculated. Hearing data were classified according to the AAO-HNS hearing classes. The nerve of origin of the tumor was specified during surgery and the largest tumor diameter was measure on MRI axial plane on T2-CISS weighed images.

RESULTS

Preoperative amplitude asymmetry ratio was lower (n = 15, Mann-Whitney U test, p < 0.001) in the group with postoperative hearing preservation (n = 11) compared with the group with postoperative hearing preservation failure (n = 4). The positive predictive value of an AR less than 24% to assess postoperative hearing preservation is 91.6%. Tumor size and localization were not correlated with cVEMPs, nor with caloric testing in this group of small-sized intracanalicular vestibular schwannomas.

CONCLUSIONS

Our data suggest that cVEMPs may help predict hearing preservation outcome in vestibular schwannoma surgery via the middle fossa craniotomy approach.

Hearing Response Following Internal Auditory Canal Decompression in Neurofibromatosis Type 2

BACKGROUND

Hearing response following an osteodural decompression of the internal auditory canal (IAC) is controversial.

OBJECTIVE

To evaluate the course of auditory brainstem responses (ABRs) and the early hearing response during the first year following IAC decompression for small to medium-sized vestibular schwannomas occurring in neurofibromatosis type 2 (NF2).

METHODS

Retrospective chart review of middle fossa craniotomy for IAC osteodural decompression in NF2-related vestibular schwannomas.

RESULTS

Twelve NF2 patients were operated on from 2011 to 2016 for IAC decompression. All had NF2 according to the Manchester criteria. All had a progressive change of their ABRs documented from the diagnosis of NF2 over a mean period of 6.25 [0.36;10.9] yr. Treatment was proposed to stop hearing progression based on the speech discrimination scores (SDSs; n = 4) or for hearing maintenance (n = 8). In patients with prior hearing progression, hearing responses were observed in 3 of the 4 patients during the first year. One patient kept on progressing. In the hearing maintenance group, the SDSs remained stable. SDSs improved from 85% [20-100] to 92.5% [60-100] on average (n = 12) and from 55% [20-80] to 77.5% [50-100] in the hearing progression group (n = 4). ABRs improved in 4 patients following decompression.

CONCLUSION

IAC decompression allows early objective hearing responses in select patients. We suggest that the procedure should be offered to patients with hearing progression based on their SDSs and/or associated progressive increases in their wave III and V latencies on ABRs.