Cystic Abducens Schwannoma without Abducens Paresis : Possible Role of Cisternal Structures in Clinical Manifestation
A 76-year-old male patient, without significant medical illnesses, presented with right facial numbness and hearing impairment for a month. The patient showed no neurological symptoms or signs except hypoestheia/hypoalgesia of the trigeminal nerve and mild hearing impairment on the right side. Magnetic resonance imaging revealed a multi-septated cystic mass on the right cerebellopontine angle (). The epidermoid cyst was excluded as a possible preoperative diagnosis based on diffusion-weighted image (). There was no enlargement of the internal auditory canal on computed tomography scans with bone window (). Pure tone audiometry and speech discrimination score showed almost normal hearing status. There were no limitations observed with the extraocculomotor movement (EOM). The preoperative diagnosis was a trigeminal schwannoma which was mainly cystic nature. Surgical resection was performed with the standard right lateral suboccipital approach. A thin-walled cystic mass displaced the lower CNs inferolaterally, the vestibulo-facial CN complex laterally, and the trigeminal nerve superiorly. After being fenestrated through its cyst wall, the mass was found to be originating from the abducens nerve. The abducens nerve seemed normal in contour and diameter, although it compressed other surrounding CNs. The tumor and its origin CN were medially located anterior to the pontine membrane and coursed within the cerebellopontine cistern (). Following a meticulous dissection, the cystic tumor was totally removed without any injury of the origin CN. Pathological examination revealed a schwannoma (). Postoperatively, the patient complained of transient diplopia without definitive EOM limitation. His symptom disappeared by 3 months after operation.