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Show Journal of Neuro- Ophthalmology 21( 3): 207- 209, 2001. © 2001 Lippincott Williams & Wilkins, Inc., Philadelphia Original Contribution Relative Pupil- Sparing Oculomotor Nerve Palsy as the Presenting Sign of Posterior Fossa Meningioma Jacqueline M. S. Winterkorn, MD, PhD, and Michiko Bruno, MD We report a case of relative pupil- sparing oculomotor paresis initially attributed to ischemia because weakness of other cranial nerves was minimal and dismissed as insignificant. Neu-roimaging eventually revealed a posterior fossa meningioma. The neurologic symptoms and signs disappeared immediately after resection of the tumor. The third nerve palsy was attributed to deformation of the brainstem. This case reinforces the importance of neuroimaging even in patients who have apparently isolated oculomotor palsy with features not classic for an ischemic etiology. Key Words: Oculomotor nerve- Third nerve palsy- Meningioma. CASE REPORT A 68- year- old woman without diabetes, hypertension, or other medical problems became aware of diplopia. Within a day or two, she noticed her right eyelid drooping, and within 3 days her eyelid was closed. She consulted an ophthalmologist and a neurologist who diagnosed an isolated right pupil- sparing third nerve paresis. Her complete blood count and blood chemistries were normal and the erythrocyte sedimentation rate was 30. A vasculopathic basis was presumed; neuroimaging was considered unnecessary and she was started on a daily aspirin. Reexamination 3 weeks later disclosed a best- corrected visual acuity of 20/ 30 OD and 20/ 15- 2 OS. Visual fields on a Humphrey 24- 2 threshold test showed superior constriction OD. The pupils were 3 mm OD and 3.25 mm OS, both reactive, but the right pupil was a bit sluggish. There was no afferent pupillary defect. The OD had reduced adduction, supraduction, and infraduction; ab- Manuscript received May 14, 2001; accepted July 9, 2001. From the Departments of Ophthalmology and Neurology and Neu-roscience New York Presbyterian- Weill Cornell University Medical Center, New York, New York. Address correspondence and reprint requests to Jacqueline M. S. Winterkorn, MD, PhD, Box 222, Roxbury, CT 06783. E- mail: jms winte @ aol. com duction was intact. The OS had intact ductions. A left hyperdeviation was present in upgaze, a right hyper-deviation in downgaze, and an exodeviation in left gaze. The right upper lid had 5 mm of ptosis. The fundus was normal. Neurologic examination revealed trace facial asymmetry, with incomplete burial of the lashes OS on forced eyelid closure ( Fig. 1). Hearing to whispered voice was subjectively decreased in the right ear. The palate elevated slightly less on the right, and the tongue deviated slightly to the right ( Fig. 2). A trace left pronator drift was demonstrated. The patient also had a tendency to turn toward the right when marching in place with eyes closed. These findings had been dismissed at the initial neurologic examination as variations of normal. Magnetic resonance imaging of the brain ( Fig. 3) demonstrated a large left posterior fossa meningioma with herniation of the cerebellar tonsils through the foramen magnum. The meningioma was resected. Two days postoperatively, all neurologic manifestations had resolved. DISCUSSION Oculomotor nerve palsy can be caused by ischemia, trauma, or compressive lesions such as aneurysms, cavernous sinus meningiomas, other primary tumors, or metastases ( 1^). The finding of greatest diagnostic significance is often considered to be the involvement or sparing of the pupil ( 5). Oculomotor nerve pareses that spare the pupil are usually attributed to microvascular ischemia, commonly associated with diabetes or hypertension ( 6). Such pupil- sparing third nerve pareses usually resolve within three months and require no intervention other than palliating the diplopia and managing the vasculopathic risk factors. Conversely, pupil paresis signals compression by tumors and aneurysms, requiring angiography and sometimes surgical intervention. Although rare cases have been reported in which pupil-sparing oculomotor nerve palsy was owing to aneurysm, Rucker's rule is based on the statistic that 95 to 97% of 207 208 J. M. S. WINTERKORN ET AL. FIG. 1. On forced eye closure, the lashes are not buried on the left, suggesting a subtle left seventh nerve paresis. aneurysms causing third nerve palsy produce pupillo-paresis ( 1,2,7). Our patient was initially diagnosed with ischemic pupil- sparing oculomotor nerve palsy because subtle signs of other cranial neuropathies were dismissed as variants of normal. However, other clues should have prompted doubt about the diagnosis of microvascular ischemia. Although the patient was 60 years old, she had no arteriosclerotic risk factors. Her extraocular muscle palsy, especially of the inferior rectus, was not complete. The pupillary reaction to direct light in the ipsilateral eye was sluggish, suggesting relative rather than absolute pupil sparing. Trobe ( 8) pointed out that the rule associating pupil- sparing with an ischemic cause should be applied cautiously, with attention to four exceptions to the rule: 1) age between 20 and 50 or lack of obvious arteriosclerotic risk factors, 2) an incomplete extraocular muscle palsy, 3) relative pupil sparing, and 4) a nonisolated third nerve palsy. In our case, the relative pupil- sparing oculomotor nerve paresis was caused by a distant contralateral posterior fossa meningioma, so that direct oculomotor compression was unlikely. Yet we believe the palsy was caused by the tumor inasmuch as the palsy cleared promptly after tumor removal. The most likely cause of the palsy was stretching of the oculomotor nerve within the subarachnoid space as it emerged from the brainstem in the interpeduncular fossa. Meningiomas can cause false localizing signs by displacing and stretching ( 9). This patient's tumor was pushing the cerebellum cau-dally and ventrally, causing the pons and medulla to deviate rightward and downward toward the foramen magnum. These actions placed the cranial nerves on stretch. A case of pupil- sparing oculomotor nerve palsy from ipsilateral acute subdural hematoma has been reported, the mechanism presumed to be mass effect on the subarachnoid portion of the oculomotor nerve ( 10). Several hypotheses can be considered to explain the pupil sparing, which was an unusual feature of this case because pupil involvement is thought to be the earliest manifestation of third nerve palsy secondary to stretch or pressure ( 9). In the case of pupil- sparing oculomotor nerve palsy from acute subdural hematoma mentioned previously, Kavieff et al. ( 10) suggested anatomic positioning within the third nerve or sheltering of pupillomotor fibers from the tentorial gap. In our case, if the forces from the tumor were exerted laterally and inferiorly as the nerve exited the brainstem, the pupillary fibers that emerge more ventrally from the Edinger- Westphal nucleus and travel medially and superiorly might be preserved ( 11). The combination of pupil sparing with incomplete inferior rectus palsy is similar to the case reported by Fleet FIG. 2. The tongue deviates slightly to the right, suggesting a very subtle right twelfth nerve paresis. / Neuro- Ophthalmol, Vol. 21, No. 3, 2001 THIRD NERVE PALSY AND MENINGIOMA 209 FIG. 3. A: Axial T1 magnetic resonance imaging ( MRI) shows a hypodense dural-based mass in the posterior fossa. B: Coronal T1 MRI with gadolinium shows an enhancing mass typical of meningioma. et al. ( 12) and adds evidence for the proximity of the inferior rectus fibers to the pupillary fibers in this proximal portion of the oculomotor nerve after its emergence from the brainstem. Alternatively, as hypothesized by Nadeau and Trobe ( 5), the small- caliber unmyelinated parasympathetic pupillomotor fibers may be more resistant to injury by slow stretch. This possibility is supported by the finding that in peripheral nerves, the mechanism of nerve injury by stretch is focal demyeli-nation ( 13). Finally, the oculomotor nerve could have been stretched more distally in the subarachnoid space. In that case, pressure exerted laterally rather medially, as is usual for carotid aneurysms and cavernous lesions, could have spared the dorsomedially situated pupillary fibers. Any deviation from the typical ischemic oculomotor nerve palsy, including duration, age, incomplete extraocular palsy, relative pupil- sparing, and any other associated neurologic signs, requires further investigation. 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Trobe JD. Third nerve palsy and the pupil. Footnotes to the rule. Arch Ophthalmol 1988; 106: 601- 2. 9. Gassel MM. False localizing signs. Arch Neurol 1961; 4: 526- 554. 10. Kavieff RD, Miller JA, Klepach GL. Pupillary sparing oculomotor palsy from acute subdural hematoma. Ann Ophthalmol 1984; 16: 387- 90. 11. Kerr FW, Hollo well OW. Location of pupillomotor and accommodation fibers in the oculomotor nerve: experimental observations on paralytic mydriasis. J Neurol Neurosurg Psychiatry 1964; 27: 473- 81. 12. Fleet WS, Rapcsak SZ, Huntley WW, et al. Pupil- sparing oculomotor palsy from midbrain hemorrhage. Ann Ophthalmol 1988; 20: 345- 6. 13. Ochoa J, Fowler TJ, Gilliatt RW. Anatomical changes in peripheral nerves compressed by a pneumatic tourniquet. J Anat 1972; 113: 433- 55. J Neuro- Ophthalmol, Vol. 21, No. 3, 2001 |
