Vestibulocochlear Swannoma

76 year-old female with long term right hypoacusia and tinnitus and 2 years of dizziness and gait instability. At medical exploration unilateral right vestibular hypo function and deafness were confirmed. There were no findings on temporal bone MRI performed 2 years ago.

Conventional MRI of the temporal bone and IAC were performed. Obliteration of right vestibule, basal and medial turn of cochlea was seen at high resolution T2-weighted 3D sequences (Figures 1a, 1b, 2). Comparison with a previous two year-old MRI exam was essential to distinguish the actual features from temporal bone MRI magnetic susceptibility artifacts (Figure 1c).
There were no high signal lesions at right inner ear on precontrast T1 – weighted imaging (not shown).
T1 MRI Gd-enhanced T1-weighted images showed a strongly enhanced lesion on the right vestibule and cochlea (Figure 3).

Vestibulocochlear schwannomas are the most common neoplasm of the cerebellopontine angle and inner ear. While most of them arise from the vestibular division of the vestibulocochlear nerve, close to the vestibular ganglion, they can also originate within the membranous labyrinth. The so-called intralabyrinthine schwannomas [1] are rare, recently about 340 cases have been reported [2].

In 2004 Kennedy et al. proposed an anatomical classification based on location and tumoral extension with 7 types of intralabyrinthine schwannomas, the intracochlear location being the most common (51%) [2, 3].
Due to the slow growth, symptoms are vague at the beginning and diagnosis can be delayed for 5 to 7 years from the first onset [3]. Sudden, fluctuating or, most commonly, progressive hearing loss are the most prevalent signs [1]. Other symptoms ordered by frequency of appearance are: tinnitus, vertigo, dizziness and facial nerve palsy [1–5].

MR imaging of the temporal bone is necessary for the diagnosis and should include both high-resolution Gd-enhanced T1-weighted and T2-weighted sequences. At T2-weighted 3D-sequences, intralabyrinthine schwannomas appear as focal filling defects with sharp borders, replacing the high signal intensity fluid of the membranous labyrinth. At Gd-enhanced T1-weighted images it appears as strongly enhanced circumscribed lesion [1, 5].

Intralabyrinthine enhancement can also be seen in other diseases as labyrinthitis, but it is usually less sharp than intralabyrinthine schwannomas, involves the whole cochlea or vestibular system [5] and there are no filling defects in membranous labyrinth on T2-weigthed images [1].
Fibrous phase in labyrinthine ossificans can enhance and be associated with filling defects in membranous labyrinth on T2-weigthed images. In these patients, temporal bone CT and previous history of meningitis or otomastoiditis are needed for the differential diagnosis [1].

Due to its low incidence, there are no guidelines about the management of the intralabyrinthine schwannomas [2].
Because of its morbidity, most patients are under “wait-and-scan” policy. Surgery is reserved for patients with extension of the schwanoma into the internal auditory canal or intractable vertigo. Radiosurgery must be considered in patients with poor health conditions with evidence of tumor growth [4].

In conclusion, in a patient with severe hearing loss, intralabyrinthine schwannomas should be suspected if a focal filling defect at T2-weighted 3D sequences with T1 Gd enhancement in a MR imaging of temporal bone is seen.

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