Ocular Tilt Reaction in Compensated Vestibular Schwannoma.

A lmost a century ago, Brain (1) initially described vestibular schwannoma as a cause of utricular dysfunction. The resultant syndrome of ocular torsion, skew deviation, and tilt of subjective visual vertical (SVV) with/without head tilt was later termed ocular tilt reaction (OTR) (2). The patient in Brain’s article (quoted from Cushing’s monograph (3)) had a large tumor causing increased intracranial pressure with displacement of the cerebellum and brainstem. A subsequent study also showed that ipsiversive SVV tilts were found in patients with large cerebellopontine angle tumors and marked compression of neighboring structures (4). We describe a patient with a vestibular schwannoma who exhibited ipsiversive OTR as the sole clinical finding and discuss a potential mechanism for a peripheral origin of OTR. A 57-year-old man reported a 3-month history of vertical diplopia at a distance. The patient could read without difficulty, but vertical diplopia developed when he watched television 4 m away. One month later, brain MRI revealed a left cerebellopontine angle tumor measuring 20 mm · 14 mm · 17 mm (Fig. 1A, B). The patient recalled that he had felt mild lightheadedness when getting out of bed and while walking. Audiometry showed a 90 dB dip at 8,000 Hz in the left ear, although he had not noticed any hearing loss. He was referred for neuro-ophthalmic evaluation. Visual acuity, color vision testing, and pupillary reactions were normal. There was no head tilt. In primary gaze, the patient had right hypertropia of 6 prism diopters that increased slightly on rightward and upward gaze. The magnitude of the vertical deviation did not change with head tilt. Measurements of the SVV with a vertical frame (binocular method) disclosed leftward tilt by 8.57°. Fundus photographs revealed a leftward torsion with 16.5° extorsion in the left eye and 2.5° intorsion in the right eye (Fig. 2A). There were no abnormalities of smooth pursuit, saccades, head impulse test, or vestibulo-ocular reflex cancellation. He did not have spontaneous nystagmus in any eye position with fixation. Deprivation of visual fixation using Frenzel goggles or in the dark with electronystagmography caused mild, right-beating, horizontal nystagmus that was enhanced by head shaking or by a left-ear-down position in the supine roll test. Left horizontal canal hypofunction was identified through bithermal caloric testing with electronystagmography. Ocular and cervical vestibular-evoked myogenic potential tests were not performed. The Romberg test disclosed a subtle body tilt to the left while other neurologic tests, including coordination of the 4 limbs, past pointing, oneleg standing, finger-to-nose, and tandem gait were normal. The average time to perform the finger-nose-finger test repeated 10 times was 6.8 seconds with the right arm and 7.6 seconds with the left; the frequency to run the heel over the contralateral shin within 30 seconds was 30 times with the right leg and 28 times with the left. The time to hold one-leg standing was 21.7 seconds with the right leg and over 30 seconds with the left. The patient performed the Four Step Square Test smoothly taking 7 seconds to finish. Despite the increasing size of the tumor (25 mm · 16 mm · 18 mm) (Fig. 1C, D), the patient’s OTR began to subside from 6 months after onset. Two months later, the patient underwent a left retromastoid craniotomy. The extracted specimen was cystic with a solid mass component arising from the vestibular nerve but sparing the internal auditory canal. To preserve the facial and auditory nerve functions, a small amount of tumor was left adherent to the nerves. Pathological diagnosis was schwannoma (WHO grade I). Over the next 10 months, the patient’s diplopia and nystagmus resolved, left canal paresis improved to 18.2% and the SVV tilt returned to the normal range. The only residual vestibular finding was 5.5° extorsion of the left eye (Fig. 2B). Brain MRI demonstrated gross removal of the tumor (Fig. 1E, F). Six years after surgery, the patient continues to remain stable. The OTR can result from any unilateral lesion of graviceptive pathways from the labyrinth to the contralateral interstitial nucleus of Cajal in the rostral midbrain through the medial longitudinal fasciculus. Graviceptive input from the utricular otoliths converges with input from the vertical semicircular canals at the level of the vestibular nuclei. Although OTR with vertical diplopia is well-described with Departments of Internal Medicine (AK), Ophthalmology (MK), and Neurosurgery (HN), St. Marianna University School of Medicine, Yokohama City Seibu Hospital, Yokohama, Japan; Department of Otolaryngology (YA), Keio University School of Medicine, Tokyo, Japan.