Isolated trochlear nerve schwannoma presenting with diplopia: A case report and literature review

Abstract

Background: Trochlear nerve schwannoma is a very rare tumor encountered especially in patients without type 2 neurofibromatosis (NF2). Most of the time, this tumor is diagnosed intraoperatively. We describe a rare case of trochlear nerve schwannoma. Clinical Presentation: A 63-year-old male presented with generalized headache from 8 months earlier, without nausea and vomiting. The headache had worsened during the last months. Clinically, he suffered from transient diplopia. Magnetic resonance imaging (MRI) demonstrated a mass in the left ambient and interpeduncular cisterns that was compressing the midbrain and upper pons. The preoperative impression was of trigeminal schwannoma. However, intraoperatively, the tumor originated in the trochlear nerve. The mass was removed entirely via left suboccipital retrosigmoid approach. The histopathology diagnosis confirmed schwannoma. The patient's diplopia did not improve postoperatively. Conclusion: Trochlear nerve schwannoma is a rare type of schwannoma and in almost all of the cases is diagnosed intraoperatively. There are three types of trochlear nerve schwannoma according to the classification proposed for trigeminal schwannoma: cisternal type-confined to the precavernous segment of the trochlear nerve; cistocavernous type-invading the cavernous sinus and the retroclival and retropetrosal cistern; cavernous type-located in the middle cranial fossa on the cavernous or paracavernous segment of the fourth cranial nerves, with or without cavernous sinus invasion. The cisternal type was the most common type encountered in previous studies. The clinical signs and symptoms of trochlear nerve schwannoma are similar to the trigeminal schwannoma and should be considered in the differential diagnosis of trigeminal schwannoma.

Peripheral orbital nerve schwannoma: Case report

“…Our patient presented with a tumor larger than the reported by 2015 by Jia Li et al of 32 x 18 x 8 compared to our case of 60 x 24 x 10mm causing asymmetry and proptosis [7]. In the orbit, schwannomas are usually unilateral and can develop from the supraorbitary, infraorbitary, supratrochlear, ciliary, oculomotor, trochlear or abducens nerve [1,[3][4][5][6][7].…”

“…The nerve of origin is not identified in up to 50% of cases 2, in our patient's case the surgical removal was difficult because of the superior oblique tendon affection. Highly cellular tumors have a higher recurrence rate and malignant transformation, thus early removal is recommended [1,[2][3][4]7]. Follow up of our patient at 3 years showed that he is asymptomatic and does not have any recurrence.…”

“…When there are cavitations within the tumor structure the imaging in heterogenous in T2 and relates to Antoni B pattern. When T2 images are more intense and homogeneous (less water content) it correlates to Antoni A pattern [1,2,4,5,[9][10][11][12].…”

“…The first description of a schwannoma was made by Smith in 1861. Previously known as Neurilemmoma is a benign tumor originating from the nerve sheath composed of schwann cells which normally produce myelin sheath covering the nerves [1][2][3][4]. Orbital schwannomas are slow growing, with less than 1% undergoing malignant transformation to neurofibrosarcoma.…”

“…They are unilateral and solitary tumors with well demarcated margins. Primary symptoms are: retroocular oppressive sensation, proptosis and in some rare cases pain [1,[3][4][5][6].…”