RESUMO

Intermediate nerve schwannomas (INS) are extremely rare lesions in literature. They have been described mimicking facial nerve schwannomas, but not vestibular schwannomas (VS). We aimed to review the previously published cases, as well as the evidence to believe that they are far more common, though usually misdiagnosed as facial or VS. We performed a review of PubMed/Medline and Embase of "intermediate nerve schwannoma," "facial nerve schwannoma," "greater superficial petrosal nerve schwannoma," "geniculate ganglion schwannoma," and "chorda tympani schwannoma" to identify all cases of INS, following the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) statement. Furthermore, 2 cases operated at our center are shown to exemplify the proposed hypotheses. No article was excluded from review. Thirteen cases of INS, 11 cases of chorda tympani schwannoma, and 18 cases of greater superficial petrosal nerve schwannoma were found in literature. In facial nerve schwannomas, the predilection of schwannomas for sensory nerves, and the ability to preserve the motor facial nerve during tumor resection support the hypothesis of intermediate nerve as the nerve of origin. For VSs, the different arachnoidal arrangement of medial VS, the sharing of pia mater by the intermediate nerve and vestibular nerve, and the medial Obersteiner-Redlich zone of the intermediate nerve, support the hypothesis of intermediate nerve origin of some VS. The correct identification of the intermediate nerve as a nerve of origin of cerebellopontine angle schwannomas is of uttermost importance, especially when mistaken for VS, as this may account for the heterogeneity of facial and cochlear outcomes after surgery.

Assuntos

Neoplasias Cerebelares/patologia , Neoplasias Cerebelares/cirurgia , Ângulo Cerebelopontino/patologia , Ângulo Cerebelopontino/cirurgia , Neurilemoma/patologia , Neurilemoma/cirurgia , Doenças do Nervo Facial/patologia , Doenças do Nervo Facial/cirurgia , Humanos , Neuroma Acústico/patologia , Neuroma Acústico/cirurgia

RESUMO

Introduction Vestibular schwannomas are the most common lesions occupying the internal auditory canal (IAC); however, almost in 4 to 5% of meningiomas, metastases, cysts, lipomas, and cavernous malformations have been found in this location, mimicking schwannomas. Even though cerebellopontine angle (CPA) meningiomas with the involvement of the IAC are frequently encountered, the presence of a primary intracanalicular meningioma is rare. Objective To show the technical nuances of the retrosigmoid-transmeatal approach to successfully achieve gross total resection (GTR) with preservation of facial and auditory function. Case Report We present a left intracanalicular meningioma on a 60-year-old man with history of tinnitus and hearing loss. Magnetic resonance imaging (MRI) showed a left intracanalicular lesion completely obliterating the IAC and with minor extension to the CPA cistern, with the vestibulocochlear complex dislocated posteriorly, initially diagnosed as a Hannover's T2 vestibular schwannoma. The patient underwent a left retrosigmoid approach, and during the exposure of the lesion, the diagnosis of a meningioma became evident. The transmeatal phase of the approach was modified with a wide opening of the canal, including the anterior wall. Closure was performed using a muscle graft, duramater flap, and fibrin glue. Results GTR was achieved and the patient developed a mild facial palsy (House-Brackmann grade III) which completely recovered within 3 months. Conclusions The retrosigmoid transmeatal approach is suitable to achieve GTR in intracanalicular meningiomas. Some modifications of the approach intended for vestibular schwannomas are necessary and may be performed during the procedure. The link to the video can be found at: https://youtu.be/A9OXRFIl1e8 .