Hamartomas of the internal auditory canal: report of two cases

To highlight the clinical, radiological, and surgical findings and therapeutic options for this rare entity, which may mimic a purely intrameatal vestibular schwannoma, and to define the particular aspects of preoperative differential diagnosis and surgical management.

Two patients presented with clinical findings typical of vestibular schwannomas, i.e., tinnitus, hearing loss of 30 dB, and an intrameatal contrast-enhancing lesion on magnetic resonance imaging studies.

The lesions were exposed via a suboccipital transmeatal approach, and tumor infiltration of the cochlear and/or facial cranial nerves was identified. In view of the unclear intraoperative histology, surgical management was based on criteria of cranial nerve function. In Patient 1, after nerve decompression by subtotal tumor removal, preserved auditory brainstem responses and facial nerve electromyography indicated functional nerve preservation and facilitated the decision for partial resection. In Patient 2, minimal tumor dissection resulted in complete loss of auditory brainstem response without reversibility. Therefore, a radical tumor removal was performed that sacrificed the cochlear but preserved the facial nerve.

Symptoms and signs of internal auditory canal hamartomas are congruent with other typical pathological lesions of the internal auditory canal and cerebellopontine angle. Accurate preoperative diagnosis by radiological means is not possible, but careful evaluation of the different signal intensities on magnetic resonance imaging studies may indicate this rare pathological condition. Intraoperative surgical findings of tumor infiltration of the faciocochlear cranial nerve complex may support simple observation. In view of the nonneoplastic characteristic of these lesions, a more conservative approach is justified. The decision should be based on the functional status of the cranial nerves, for which reliable electrophysiological monitoring is indispensable.