Recurrent Third Nerve Palsy Secondary to Instrinsic Schwannoma of the Third Cranial Nerve

Photo and Video Essay Section Editors: Melissa W. Ko, MD Dean M. Cestari, MD Peter Quiros, MD Recurrent Third Nerve Palsy Secondary to Instrinsic Schwannoma of the Third Cranial Nerve Edward Margolin, MD, Trishal Jeeva-Patel, MD, Laila Al Shafai, MD FIG. 1. A. Coronal FIESTA sequence. B. Axial reformats of the FIESTA sequence. Right third nerve is larger than the left. Arrow: right cisternal (A) and left intracavernous portions (B). Arrowhead: Left cisternal (A) and left intracavernous (B) portions. FIESTA, Fast-Imaging Employing Steady-State Acquisition. Abstract: A 78 year-old woman has experienced multiple episodes of transient right third nerve palsy over the course of 15 years and has undergone multiple imaging studies as well as investigations for myasthenia gravis and giant cell arteritis in search for the diagnosis. When seen after the most recent episode, MRI with contrast and Fast-Imaging Employing Steady-State Acquisition protocol revealed a subtle enlargement and enhancement of the cisternal and proximal cavernous portions of the right third cranial nerve. An empiric diagnosis of schwannoma intrinsic to third cranial nerve was made. All patients with cyclical third nerve palsies should have appropriate neuroimaging to rule out subtle structural lesions before other investigations are undertaken. Journal of Neuro-Ophthalmology 2021;41:e232–233 doi: 10.1097/WNO.0000000000000994 © 2020 by North American Neuro-Ophthalmology Society W e present a well-illustrated case of a patient with multiple episodes of recurrent pupillary-sparing third Departments of Ophthalmology and Vision Sciences (EM, TJ-P)and Medical Imaging (LAS), University of Toronto, Toronto, Canada. The authors report no conflicts of interest. Address correspondence to Edward Margolin, MD, FRSCS, University of Toronto Faculty of Medicine, Department of Ophthalmology and Department of Medicine (Neurology), 801 Egilnton Avenue, West Suite 301, Toronto, ON m5N 1E3, Canada; E-mail: edward. [e-mail] e232 nerve palsy (TNP) over the course of 15 years, which was finally determined to be secondary to presumed schwannoma intrinsic to the cisternal and proximal intracavernous portion of the third cranial nerve. Schwannomas intrinsic to the third nerve are very rare, they sometime present with cyclical episodes of cranial nerve dysfunction, and are best appreciated on postcontrast balanced steady-state echo sequence on MRI. A 78 year-old woman was first diagnosed with the right pupillary-sparing TNP palsy 15 years ago when she presented with complete ptosis and limitation of supra-, infero- and adduction. CT and CT angiography (CTA) of the brain were interpreted as normal. All symptoms have spontaneously resolved over 1–2 months. She then had another similar episode 2 years later. CT and CTA of the brain were repeated and again interpreted as normal; temporal artery biopsy was performed as the diagnosis of giant cell arteritis was entertained and was normal. Workup for myasthenia gravis (acetylcholine receptor antibodies, singlefiber electromyelogram, and endrophonium testing) was negative as well. She then had at least 4 more episodes over the next 10 years of right upper-lid ptosis and diplopia accompanied by various degrees of dysfunction of extraocular muscles supplied by the third nerve, each time with complete recovery of function after 1–2 months. She had a total of 7 CTAs of the brain, 2 MRI/MRAs of the brain and neck, 3 single-fiber EMGs, and 2 temporal artery Margolin et al: J Neuro-Ophthalmol 2021; 41: e232-e233 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Photo and Video Essay FIG. 2. A. Coronal T1 post gadolinium sequence. B. Reformatted sagittal plane. Diffuse enlargement and enhancement of right third cranial nerve in its intracavernous (arrow) and cisternal (arrowhead) segments. biopsies, and was treated with high-dose oral steroids for 6 months after the last 2 episodes for the presumed diagnosis of giant cell arteritis. She was symptom-free for 2 years when she presented to our clinic with the partial right upper-lid ptosis and deficits in supra-, infero-, and adduction of the right eye. There was minimal anisocoria with the right pupil being 1 mm larger than the left and a diagnosis of pupillary-involving right partial TNP was made. There were no other associated symptoms, and neurological examination was otherwise normal. MRI and MR angiography of the brain with contrast and Fast-Imaging Employing Steady-State Acquisition protocol to evaluate the entire course of the right third nerve was performed 2 weeks after symptoms have resolved. It revealed subtle enlargement of the cisternal and proximal intracavernous portion of the right third cranial nerve compared to the contralateral side (Fig. 1). The enlarged area was enhancing after administration of gadolinium (Fig. 2). When previous imaging was reexamined, subtle thickening of the cisternal portion of the right third nerve was seen then as well (although both studies did not deploy balanced steady-state echo sequences protocol and were performed without contrast). Diagnosis of schwannoma intrinsic to the right third cranial nerve was empirically made. Schwannomas represent about 7%–8% of all intracranial tumors and most commonly involve eighth or fifth cranial nerves (1). Schwannomas intrinsic to the third nerve are very rare and less than 40 cases have been described in the literature (2). Cases with both permanent dysfunction of the nerve and cases with cyclical episodes of third nerve palsies were described (3,4). When considering a differential diagnosis of a patient with cyclical third nerve palsy, the only other conditions that could cause it are ophthalmoplegic migraine (OM) and myasthenia gravis. In OM, there is often thickening and enhancement of the third cranial nerve on imaging seen during the episodes of TNP accompanied by headaches with resolution of neuroimaging findings in between the episodes. The etiology of OM was proposed to be transient demyelination or inflammation of the third Margolin et al: J Neuro-Ophthalmol 2021; 41: e232-e233 nerve (5). In some cases of OM, third nerve thickening and sometimes enhancement persisted between the episodes thus making the diagnosis of schwannoma a more likely possibility in at least some previously described cases of OM (4). Most previous cases of oculomotor nerve schwannoma involved the cisternal portion of the nerve and in our patient, it extended to involve the intracavernous portion of the nerve. Although the mechanism of recurrent episodes of nerve dysfunction is unknown, the proposed theories include transient swelling within the tumor, remyelination, and hemodynamic changes (4). In our patient, neuroimaging demonstrating thickened and enhancing portion of the third nerve was obtained after all symptoms have resolved demonstrating transient nature of symptoms in the presence of a structural lesion, which is what has been described in other cases of oculomotor schwannomas (4). Although the definitive diagnosis of schwannoma requires a biopsy, it can presumptively be made based on neuroimaging characteristics of a focal thickening of the cranial nerve with enhancement on postcontrast images. This case reminds us of the need to obtain detailed neuroimaging with contrast in patients with cranial nerve palsies, evaluating the entire course of a cranial nerve to rule out a structural lesion affecting the nerve before the diagnosis of neuromuscular junction disorder is made or a rare possibility of giant cell arteritis presenting with an isolated cranial nerve palsy is considered. A neuroimaging protocol allowing for high special resolution with image contrast between the cranial nerve and cerebrospinal fluid (balanced steady-state echo sequences) should be used in all these cases. STATEMENT OF AUTHORSHIP Category 1: a. Conception and design: E. Margolin, T. Jeeva-Patel, and L. Al Shafai; b. Acquisition of data: E. Margolin, T. Jeeva-Patel, and L. Al Shafai; c. Analysis and interpretation of data: E. Margolin, T. Jeeva-Patel, and L. Al Shafai. Category 2: a. Drafting the manuscript: E. Margolin; b. Revising it for intellectual content: E. Margolin, T. Jeeva-Patel, and L. Al Shafai; Category 3: a. Final approval of the completed manuscript: E. Margolin, T. Jeeva-Patel, and L. Al Shafai. REFERENCES 1. Feinberg AS, Newman N. Schwannoma in patients with isolated unilateral trochlear nerve palsy. Am J Ophthalmol. 1999;127:183–188. 2. Marutirao R, Singh S, Bhasiora KS, Pandey S, Sardhara J, Das KK, Srivastava AK, Jaiswal S, Behari S. Sporadic cisternal oculomotor nerve schwannoma: a rare case with review of literature. Asian J Neurosurg. 2018;13:1269–1272. 3. Bentley E, Ved R, Hayhurst C. Oculomotor schwannoma causing a progressive complete third-nerve palsy. BMJ Case Rep. 2019;12:e230272. 4. Shin RK, Mejico LJ, Kawasaki A, Purvin VA, Moster ML, Younge BR, Boghen D. Transient ocular motor nerve palsies associated with presumed cranial nerve schwannomas. J Neuroophthalmol. 2015;35:139–143. 5. Lance JW, Zagami AS. Ophthalmoplegic migraine: a recurrent demyelinating neuropathy? Cephalalgia. 2001;21:84–89. e233 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited.