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Show Journal of Ncuro- Ophthalmology 15( 1): 11- 14, 1995. © 1995 Raven Press, Ltd., New York Monocular Elevation Paresis Caused by an Oculomotor Fascicular Impairment Chiaki D. Gauntt, M. D., Satoshi Kashii, M. D., Ph. D., and Izumi Nagata, M. D., Ph. D. A 54- year- old man developed an acquired monocular elevation paresis. Forced lid closure or oculocephalic reflexes failed to elevate the affected eye in contrast to the contralateral eye, which turned fully upward using either maneuver. A mass lesion compressing the lateral aspect of the right oculomotor nerve at the exit of the brainstem was found. The monocular elevation paresis in this patient reflects damage of the oculomotor nerve fascicles that supply the inferior oblique and superior rectus muscles. This case supports the accepted topographical fascicular arrangement of the oculomotor nerve, with the inferior oblique and superior rectus being the most lateral and caudal, and the pupilloconstric-tor fibers and the inferior rectus being most medial and rostral. Key Words: Monocular elevation paresis- Oculomotor nerve- Midbrain- MRI. Manuscript received March 21, 1994; accepted May 31, 1994. From the Departments of Ophthalmology ( C. D. G., S. K.) and Neurosurgery ( I. N.), Faculty of Medicine, Kyoto University, Japan. Address correspondence and reprint requests to Dr. Satoshi Kashii, Department of Ophthalmology, Faculty of Medicine, Kyoto University, Sakyo- ku, Kyoto, 606, Japan. Monocular elevation paresis was originally described secondary to a supranuclear impairment of oculomotor nerve function. We report a case with monocular elevation paresis due to damage of the oculomotor nerve fascicles supplying the inferior oblique and superior rectus muscles. The case provides information regarding the topographical arrangement of the oculomotor fascicles. CASE REPORT A 54- year- old man was referred by his neurosurgeon because of diplopia. Two years prior to presentation, he first noted vertical binocular diplopia on upward gaze and some unilateral headaches that had subsided before long. Although diplopia had been present on and off since then, it became more prominent and finally unbearable in the 2 weeks prior to hospitalization in the Department of Neurosurgery, Kyoto University Hospital. His past medical history was not significant. On examination, his best corrected visual acuity was 20/ 30 in the right eye a n d 20/ 15 in the left eye. Both pupils were normal and briskly responded to light and near stimulation. There was a left hyperphoria of 2 prism diopters in primary gaze, which remained the same with right or left gaze. Upward gaze produced 20 prism diopters of left hypertropia. There was 5 prism diopters left hyperphoria with right or left head tilt. Supraduction of the right eye was equally limited in both adduction and abduction ( Fig. 1). The elevation deficit of the right eye could not be overcome by either oculocephalic maneuvers ( vestib-ulo- ocular reflex) or forced eyelid closure ( Bell's phenomenon) ( Fig. 2). Downward gaze was not limited, and there was no limitation of any movement in the left eye. There was no nystagmus. 11 12 C. D. GAUNTT ET Ah. FIG. 1. Ocular positions of gaze. Supraduction of the right eye was equally limited in both adduction and abduction. The downward movements of the right eye were normal, as were all movements in the left eye. There was no ptosis. Convergence was normal. There was no ptosis or proptosis. All other cranial nerves were functioning normally. Slit- lamp and other ophthalmoscopic examinations were unremarkable. Edrophonium chloride test and forced duction tests in both eyes were negative. Magnetic resonance imaging ( MRI) of the brain revealed a space occupying lesion of high signal intensity on Tl- weighted images located where the right oculomotor nerve leaves the brainstem ( Fig. 3). Surgical removal of the tumor was performed 2 weeks after our initial examination. Intraoperative observations confirmed a mass compressing the lateral aspect of the root of the right oculomotor nerve inwardly at the exit from the brainstem. Postoperative histopathologic studies on the surgical specimen demonstrated an angioma. Postoperatively, the patient developed complete right oculomotor nerve palsy with pupillary involvement. DISCUSSION The patient described in this report presented clinically with acquired " monocular elevation paresis" of the right eye. There was no evidence of restrictive ophthalmoplegia, such as orbital floor fracture, dysthyroid ophthalmopathy, or Brown's tendon sheath syndrome, as noted by the absences of ocular motility restriction, enophthalmus or proptosis, as well as the normal orbital computed tomographic scan ( 1,2). Negative edrophonium chloride test excluded myasthenia gravis, which can mimic any kind of ocular motor nerve paresis ( 3). The elevation deficit of the affected eye was equally severe in both adduction and abduction in this patient. By contrast, the affected eye demonstrated unimpaired full adduction and depression, as were all movements in the contralateral eye. There was no ptosis or anisocoria. A syndrome of adult onset monocular elevation paresis of pretectal origin has been well recognized since 1968, when Jampel and Fells ( 4) first differentiated it from the congenital form of double elevator palsy. Acquired monoclar elevation paresis is characterized by sudden onset of vertical diplopia, primarily occurring during upward gaze, and retention of normal Bell's phenomena in the affected eye ( 5). It remains controversial whether . the site of the responsible lesion in the midbrain pretectum is ipsi-lateral or contralateral to the affected eye ( 6- 8). In the present case, however, unilateral absence of Bell's phenomena and vertical vestibulo- ocular reflex of the affected eye, despite preserved elevation of the contralateral eye, was diagnostic of the infranuclear origin of the disorder. Based on a case of isolated inferior oblique muscle paresis due to ventral midbrain infarction and a review of the literature, Castro and his associates ( 9) proposed the mediolateral somatotopy of the oculomotor fascicular fibers within the mesencephalon with the inferior oblique and superior rectus being most lateral and the pupilloconstrictor fibers and the inferior rectus being most medial. Furthermore, taking account of the monocular elevation weakness and ptosis due to midbrain infarction involving the fasicular oculomotor nerve / Neuw- Ophthalmol, Vol. 25, No. 1, 1995 MONOCULAR ELEVATION PARESIS 13 ( 10), Johnson and Castro ( 11) also suggested that the levator palpebrae fascicles are in an intermediate location between the superior rectus and medial rectus fascicles. The site of compression in our case was the lateral side of the oculomotor nerve immediately as it left the brainstem. It is conceivable that the long- standing tumor compression in our patient would have impinged upon a localized area of the nerve being compressed and produced impairment of the laterally situated fasicles supplying the superior rectus and inferior obliques. Thus, the clinical picture in our patient favors the proposed transverse neuroanatomic organization of the fascicular fibers of the oculomotor nerve proposed by Castro and his associates ( 9). That is, mediolateral somatotopy with the superior rectus and inferior obliques being most lateral, also appropriately describes the immediate nerve fibers at the exit from the cerebral peduncle. As for the distribution of the inferior rectus and FIG. 2. TOP: Elevation deficit of the right eye during upward gaze. Middle: With forceful closure of the eyelids, the right eye does not elevate, whereas the left eye does. Bottom: Oculocephalic maneuvers fail to elevate the right eye. By contrast, the left eye is elevated by these maneuvers. FIG. 3. A T1- weighted image of the midbrain showing a large mass with hyperintense signal compressing the lateral aspect of the oculomotor nerve at the exit of the brainstem. pupillary fascicles, we must consider the rostro-caudal representations of the oculomotor nerve subnuclei as well. As Burde and his associates ( 12,13) indicated, the fascicular oculomotor nerve fibers have a rostral caudal somatotopy within the mesencephalon with parasympathetic fibers being most cephalad, followed by the inferior rectus in the rostral part of the oculomotor complex. Thus, the preserved functions of the pupillary sphincter as well as the inferior rectus muscles in our patient may reflect intact rostral fascicles and suggest the caudal location of the oculomotor nerve fibers being impaired by the tumor. According to Warwick ( 14), the oculomotor nerve divides into a superior branch containing fibers to the levator palpebrae superioris and superior rectus muscles and an inferior branch containing fibers to the medial rectus, inferior rectus, inferior oblique muscles, and pupilloconstrictor fibers, in the cavernous sinus. However, recent clinical case reports demonstrate that the functional separation of the oculomotor nerve into superior and inferior divisions occur before its anatomic bifurcation in the cavernous sinus ( 15- 17). Guy and Day ( 16) reported three patients with unilateral ptosis, supraduction deficit, and normal pupils, who had basilar artery aneurysms compressing the interpeduncular oculomotor nerve from below and medially. They claimed that superior division paresis of the oculomotor nerve could oc- / Neuro- Ophthalmol, Vol. 15, No. 1, 1995 14 C. D. GAUNTT ET AL. cur before its anatomic bifurcation in the cavernous sinus. Their observation that superior division of the oculomotor nerve was affected from below by an aneurysm located inferiorly to the nerve indicates that aneurysmal compression does not always exert its effect on the site of attachment, if indeed the segregation has already occurred at the site of compression. In terms of divisional oculomotor nerve paresis, the function of the inferior oblique muscle plays a crucial role in establishing the diagnosis. However, some of the previous case reports seemed to assume the diagnosis without specifying the functions of the inferior obliques in each patient. Recently, Burde and his colleagues ( 18) proposed a three- dimensional model of oculomotor nerve subnuclei based on studies in nonhu-man primates as well as patients. Based on this model, the caudally located fasicles contain fibers primarily subserving the inferior oblique, superior rectus, and levator palpebrae, whereas rostrally located fascicles primarily consist of pupillary fibers, and those subserving the inferior rectus. Thus, limitation of supraduction with ptosis, such as seen in the patients reported by Guy and Day ( 16), could have been secondary to the impairment of the caudally located fibers at their exit from the brainstem. If this was the case, the site of aneurysmal attachment becomes the site of the most affected fibers. It is obvious that topographical distribution is already present among the fascicular fibers of the oculomotor nerve within the mesencephalon ( 12,13). Where oculomotor fascicles merge to conform with superior and inferior divisions is yet to be elucidated. It is, thus, all the more important for a neuro- ophthalmologist to evaluate and describe each function of extraocular muscles specifically for better understanding of the functional anatomy of the oculomotor nerve. REFERENCES 1. Sergott RC, Glaser JS. Graves' ophthalmopathy. Surv Ophthalmol 1981; 26: 1- 21. 2. Wang FM, Wertenbaker C, Behrens MM, et al. Acquired Brown's syndrome in children with juvenile rheumatoid arthritis. Ophthalmology 1984; 91: 23- 6. 3. Van Dyk HJL, Florence L. The tensilon test: a safe office procedure. Ophthalmology 1980; 87: 210- 12. 4. Jampel RS, Fells P. 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