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LETTERS TO THE EDITOR

Transcanal Transpromontorial Approach to Vestibular Schwannoma: Are We There Yet?

Prasad, Sampath Chandra M.S., D.N.B., F.E.B.-O.R.L.H.N.S.; Sanna, Mario M.D.

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doi: 10.1097/MAO.0000000000001822
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Dear Sir,

It is with great interest that we read the article titled “Transcanal Transpromontorial Acoustic Neuroma Surgery: Results and Facial Nerve Outcomes” (1). The authors analyze their modest series of 49 patients in whom they performed an endoscopic transcanal transpromontorial approach for resection of Vestibular Schwannomas (VS).

Before they claim that this approach be considered as a minimally invasive and conservative approach for the management of VS, the following issues need to be addressed and debated:

  • 1. The selection criteria mention that tumors extending from fundus to porus of the internal auditory canal were included in the study. Subsequently, the results show that one of the tumors (Fig. 1B) was reaching the brainstem (Koos III) and was beyond the porus, in conflict with the selection criteria. We raise this point because the size of tumor plays an important role in the selection of approach.
  • 2. The authors mention that the decision to operate was based on preoperative tumor growth but fail to mention the criteria they adopted to measure and demonstrate tumor growth. Our study (2) showed that intrameatal tumors were the slowest to grow among all tumor sizes and in fact 70% of the intrameatal tumors did not grow at all. When our wait-and-scan policy was applied to intrameatal tumors, 86% of them escaped surgery.
  • 3. The preop hearing loss was moderate to total hearing loss (Class D of AAO-HNS classification for hearing) in all patients. In this context, when hearing is already lost, and we know that such low volume tumors grow the slowest of all grades of VS, we recommend that the need to operate on such patients needs to be reconsidered. The only indication for surgery in such patients can be intractable vertigo or other symptoms that seriously debilitates the patient. However, this is very rare. In such cases, our experience has shown that the use of intra-tympanic gentamycin works very well and again, surgery is avoidable (3).
  • 4. The transcanal transpromontorial approach itself involves destruction of the cochlea and closure of the external auditory canal. Destruction of the cochlea is unacceptable in such small tumors as it closes the option of performing a cochlear implantation to rehabilitate hearing. We have published our good results after simultaneous ipsilateral cochlear implantation after VS when the cochlear nerve can be preserved after translabyrinthine approach to VS (4,5). Other authors propagating such an approach also describe drilling out the anterior wall of the external canal to get a better angulation thereby exposing the temporomandibular joint leading to additional morbidity.
  • 5. The age of the patient also plays an important factor in decision making in intrameatal tumors. Although the details are not available, the authors have indicated that a few of their patients were above 65 years (age range was 27–77 yr). Wait-and-scan, and not surgery, must be the first option in such patients and unless a very fast growth is demonstrated these patients can escape surgeries completely (2).
  • 6. The cerebrospinal fluid leak rates (7.4%) in what the authors call conservative or minimally invasive surgery are about 10 times more than the incidence of the same (0.85%) in our published series of 1,865 patients of which over 41% of the tumors were large tumors (> 20 mm) in the cerebellopontine angle.
  • 7. The authors compare their facial nerve (FN) results with our series of VS removed via translabyrinthine approach and conclude that their postoperative FN results of House-Brackmann I and II were 95.9% in comparison with ours which was 59.87%. This comparison is unscientific and rather imprudent as the authors fail to draw to the attention of the readers the fact that in our large series of 1,865 patients, 1,542 (88.5%) of the tumors were grade I (extrameatal) tumors, and 561 (32.2%) of them were grade III to V tumors (> 20 mm in the cerebellopontine angle) (6). A meaningful comparison would be when the postoperative FN outcomes 200 of our patients in whom the tumor was intrameatal (grade 0) were to be compared with the authors series of intrameatal tumors. Here, it turns out that that our FN results (House-Brackmann I & II) after translabyrinthine approach in 200 intrameatal tumors turn out to be 92.5% which is comparable to the authors’ results of 95.9% in 49 patients.
  • 8. Finally, the duration of follow-up of the current series is 14 months (the authors have included a follow-up of even 2 mo) which is too short a period to determine definitive postoperative results.

This apart, there are several other issues that need to be discussed before claiming that the present technique is superior to the existing techniques. The dissection in a transcanal transpromontorial technique is done with a single hand approach. This could be dangerous while dealing with tumors in the cerebellopontine angle. Also, how do the authors propose to manage a large bleed that can occur from the tumor or from surrounding vasculature, albeit rarely, with such a narrow approach to the cerebellopontine angle, that too with a single hand?

Although the authors must be complemented for exploring this approach and presenting their experience, they must be cautious in over-emphasizing the usefulness and advantages of this approach over other existing microscopic approaches.

REFERENCES

1. Marchioni D, Soloperto D, Masotto B, et al. Transcanal transpromontorial acoustic neuroma surgery: Results and facial nerve outcomes. Otol Neurotol 2018; 39:242–249.
2. Prasad SC, Patnaik U, Grinblat G, et al. Decision making in the wait-and-scan approach for vestibular schwannomas: Is there a price to pay in terms of hearing, facial nerve, and overall outcomes? Neurosurgery 2017; Epub ahead of print.
3. Giannuzzi AL, Merkus P, Falcioni M. The use of intratympanic gentamicin in patients with vestibular schwannoma and disabling vertigo. Otol Neurotol 2013; 34:1096–1098.
4. Sanna M, Medina MD, Macak A, Rossi G, Sozzi V, Prasad SC. Vestibular schwannoma resection with ipsilateral simultaneous cochlear implantation in patients with normal contralateral hearing. Audiol Neurootol 2016; 21:286–295.
5. Lassaletta L, Aristegui M, Medina M, et al. Ipsilateral cochlear implantation in patients with sporadic vestibular schwannoma in the only or best hearing ear and in patients with NF2. Eur Arch Otorhinolaryngol 2016; 273:27–35.
6. Kanzaki J, Tos M, Sanna M, Moffat DA, Monsell EM, Berliner KI. New and modified reporting systems from the consensus meeting on systems for reporting results in vestibular schwannoma. Otol Neurotol 2003; 24:642–648.
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