Response to “Intralabyrinthine Schwannomas

Abstract

To the Editor We read with great interest the article titled “Intralabyrinthine Schwannomas: A Case Series With Discussion of the Diagnosis and Management” by Bouchetemplé et al., published in issue 34 of Otology & Neurotology (1). In that article, three cases of intralabyrinthine schwannomas (ILSs) and six cases of internal acoustic canal schwannomas with intralabyrinthine extension (IAC-ILS) are reported, and a literature review is presented to propose a management protocol. The Authors claim that “frequency of ILS is underestimated because of poor diagnostic criteria” and broadly compare ILS with Ménière’s disease. In particular, they discuss a diagnostic routine comprising auditory and vestibular tests. They found a consistent hearing loss of varying degrees in all their patients but state that auditory brainstem responses are not a reliable screening tool because they might be unobtainable because of severe hearing loss and because auditory brainstem responses will not reveal a retrocochlear dysfunction if the lesion is only intralabyrinthine. With regard to vestibular tests, the authors state that they performed caloric and gaze tests as well as saccades and pendular tracking tests in six of their patients and found two of them with areflexia and one with hyporeflexia. The golden standard in ILS is, of course, magnetic resonance imaging with the injection of a contrast agent. We have two patients with ILS (whose cases are being prepared for publication) who recently presented to our attention, one with a cochlear and one with an utricular location. Both were males, and both presented with hearing loss and tinnitus. The patient with the utricular ILS showed postural instability and general unsteadiness that evolved into vertigo, whereas the one with cochlear ILS had no vestibular symptoms at all. We performed the same routine proposed by Bouchetemplé et al., with the addition of ocular and cervical vestibular evoked myogenic potentials (oVEMPs and cVEMPs, respectively). VEMPs are myogenic responses that are evoked by sound, vibration, or electrical stimulation and can be recorded with surface electrodes on the sternocleidomastoid muscle (cVEMPs) or on the extraocular muscles (oVEMPs). In cVEMPs, sound stimulates saccular receptors (2) and, via the vestibulocollic reflex, impulses (involving the inferior vestibular nerve) are sent to the neck muscles via the medial vestibulospinal tract, mostly on the ipsilateral side. In oVEMPs, sound stimulates utricular receptors (3) and reflexes are sent via the vestibulo-ocular pathways (through the superior vestibular nerve) to the contralateral extraocular muscles. The anatomic and functional integrity of the utricular and saccular receptors is essential for the presence of these potentials. In both patients, oVEMPs were absent in the affected ear while were normal in the unaffected ear, whereas cVEMPs were normal in both ears in both patients. The complete absence of oVEMPs in our patients with ILS is a different finding from that of patients with Ménière’s disease. On the basis of our experience, we believe that oVEMPs should be included in the diagnostic routine for intralabyrinthine mass-occupying lesions, although it cannot replace magnetic resonance imaging in perfecting diagnosis and follow-up in such diseases. oVEMP testing has been recently introduced (4) in the evaluation of part of the vestibular apparatus (especially the utricle and the vestibular nerve higher), and they might help in diagnosing intralabyrinthine mass-occupying lesions to improve those “poor diagnostic criteria.” Giovanni Ralli Department of Sensory Organs Policlinico Umberto I University of Rome “Sapienza” Rome, Italy Filippo Mazzei A.I.R.S. onlus Italian Association for Research on Deafness Rome, Italy [email protected] Giancarlo Altissimi Giancarlo Cianfrone Department of Sensory Organs Policlinico Umberto I University of Rome “Sapienza” Rome, Italy