Teaching Case

A 60-year-old man comes to the otorhinolaryngologist with symptoms of pulsatile tinnitus and progressive sensorineural hearing loss at the left side. He had no history of otitis media or trauma in our hospital. An MRI was requested to exclude vascular, neural or bony lesions.

The patient underwent an MRI examination on a 3T-magnet, and 3D T1-weighted images and T2-weighted images before and after gadolinium were obtained.
On high-resolution T2-weighted MRI, a focal signal loss in the left cochlea was found (Fig. 1). On thin-section, 3D T1-weighted MRI, there was a slightly hyperintense T1-signal in the left cochlea compared to CSF (Fig. 2) and after gadolinium administration a focal enhancing mass with more or less sharp borders was seen at the same location (Figs. 3 and 4).
For further differentiation between labyrinthitis ossificans and intralabyrinthine schwannoma an additional CT was taken, showing no calcifications in the scala tympani of the cochlea (Fig. 5).

A. Schwannoma is a benign neoplasm developing from the Schwann cells of the nerve sheath. When they arise from the branches of the vestibulocochlear nerve within the labyrinth and initially do not have a component in the internal acoustic canal (IAC), they are called "intralabyrinthine schwannomas"(ILS) or primary inner-ear schwannomas (PIES) [1]. Van Abel Et al. [2] suggest using the term primary inner-ear schwannomas instead of ILS to prevent confusion when classifying them.
Primary ILSs are estimated to account for approximately 10% of all vestibulocochlear schwannomas making them extremely rare [1], nevertheless a recent systematic review in 2015 found 234 cases [3].
B. They found that the average age was 49 years, with no male-female predilection and almost all patients with ILS presented with symptoms of unilateral sensorineural hearing loss. Other symptoms were vertigo, motion-induced dizziness and disequilibrium [3].
C. The diagnosis of ILS is ultimately made with MRI by performing high-resolution T2-weighted MRI and contrast-enhanced T1-weighted scan. Typically, there will be a lack of normal hyperintense signal on T2-weighted imaging and a correlating enhancement on the gadolinium-enhanced T1-weighted scan. The T2-weighted sequence makes it possible to distinguish in which scala the ILS is located. [1]
Kennedy et al. [4] was the first to make a classification according to the site of the tumour (table): intracochlear, intravestibular, intravestibulocochlear, transmodiolar, transmacular, transotic and tympano-labyrinthine were described. Ten years later Van Abel et al. added two more: translabyrinthine and those that involve the cerebellopontine angle. The most frequent ILS is the intracochlear ILS (approximately 80%) [2]. Of the intracochlear ILS most are situated anterior in the cochlea in the transition area between basal and second turn, and they are always located purely in the scala tympani or in both the scalae. This is due to the proximity of the nerve to the scala tympani in the region where it leaves the osseous spiral lamina.
D. The further management of ILS is made on tumour location and size and by the severity of symptoms. When patients experience severe vertigo or when the tumour grows into the middle ear, cerebellopontine angle (CPA) or intern acoustic channel (IAC) surgery is required. Otherwise follow-up of tumour growth with MRI is enough. [1-6]
E. Take Home Message:
1. Have a heightened awareness for the vestibular schwannomas
2. Make sure to classify them correctly with extra attention to tumour growth into the middle ear, CPA and IAC
Written informed patient consent for publication has been obtained.