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Show Journal of Neuro- Ophthalmology 16( 1): 9- 13, 1996. > 1996 Lippincott- Raven Publishers, Philadelphia Bilateral Optic Neuritis Originating in a Single Chiasmal Lesion A Case Report Joern B. Soltau, M. D., and William M. Hart, Jr., M. D., Ph. D. Abstract: A case of bilateral retrobulbar optic neuritis with profound visual loss is described. Magnetic resonance imaging ( MRI) with fat- saturation suppression and gadolinium enhancement done 15 days after the onset of symptoms demonstrated bilateral posterior optic nerve disease in a pattern similar to that seen in previously reported cases. However, subsequent retrospective review of an MRI study done at a different hospital during the first week of disease demonstrated a single focus of gadolinium enhancement within the body of the chiasm. This observation suggests that bilateral demyelination of the posterior optic nerves may begin as a single focus of chiasmal disease that then spreads to involve the proximal portions of the optic nerves. Key Words: Bilateral- Chiasmal- Retrobulbar- Optic neuritis- MRI- Intravenous methylprednisolone. Manuscript received April 4, 1995. From the Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, Missouri, U. S. A. Address correspondence and reprint requests to Dr. William M. Hart, Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, Box 8096, 660 S. Euclid Avenue, St. Louis, MO 63110, U. S. A. Optic neuritis is an acute demyelinating disease of the optic nerve, often occurring in patients with confirmed multiple sclerosis ( MS) or as the initial presentation of MS ( 1). It may also be an isolated finding, in which case it may represent a forme fruste of MS ( 2). Bilateral disease is not uncommon, but it has not yet been studied extensively by magnetic resonance imaging ( MRI) ( 3,4). Bilateral-ity may be more common than once supposed ( 5). In patients with isolated optic neuritis, MRI of the brain has shown lesions in 46.9%. With the administration of i. v. gadolinium, enhanced optic nerve lesions can be demonstrated in about half of patients with acute optic neuritis ( 6), and this degree of sensitivity can be improved when an appropriate fat- suppression technique is used ( 7). The demyelinating events in disseminated sclerosis occur in random, unpredictable sequences, and although lesions may tend to cluster in certain regions, they do not form patterns of bilateral symmetry. It seems odd, then, that bilateral simultaneous involvement of the optic nerves is not uncommon. We present a patient with bilateral optic neuritis in whom we could document a single focus of acute gadolinium enhancement in the chiasm on MRI, with subsequent migration of the signal enhancement into the proximal ( intracranial) segments of both optic nerves over a 2- week period, leaving behind a nonenhancing chiasm. This observation may help explain the tendency for simultaneous bilaterality to be found in optic nerve demyelinating disease. CASE REPORT A 66- year- old white woman was seen after a 2- week history of bilateral visual loss; she had extremely limited light perception in her right eye 9 10 ]. B. SOLTAU AND W. M. HART, JR. and " hand- motion" vision in her left eye. Her past medical history was significant for hiatal hernia, untreated hypercholesterolemia, and an anxiety disorder. The patient also described having had an episode of unexplained sensory disturbances in her legs in the late 1970s. Neurological evaluation at that time had negative results. In addition, the patient had had a benign tumor removed from the right parotid gland in 1975. The patient's initial visual complaint had been sudden- onset blurring and diplopia, for which she had been admitted to an outside hospital. Fundu-scopic examination, ocular movements, and pupillary reactions had been described as normal. Visual acuity had not been recorded, nor was the visual field examined. Physical examination was normal except for a blood pressure of 180/ 76 mm Hg. Findings of an evaluation including carotid Doppler ultrasonography, electrocardiogram ( ECG), echocardiogram, and computed tomography ( CT) scan of the brain ( without contrast, 10- mm slices) were reported to be normal. MRI scan of the brain with and without gadolinium enhancement was also said to be normal except for a 1.5- cm right parotid gland tumor, which showed a signal pattern consistent with a pleomorphic adenoma. One week after symptom onset, the patient was seen by her ophthalmologist, who recorded visual acuity as " hand motions" in both eyes. Pupils were described as equally reactive to light without relative afferent pupillary defect. Intraocular pressures by applanation tonometry were 30 mm Hg in the right eye and 25 mm Hg in the left eye. Slit-lamp biomicroscopy and indirect ophthalmoscopy were both recorded as normal. Two weeks after symptom onset, the patient was referred to our office. Visual acuity at that time was bare light perception in the right eye and hand motions in the left eye. There was no recordable visual field in either eye with the largest, brightest test object of the Goldmann perimeter. A relative afferent pupillary defect was now weakly evident in the right eye. Intraocular pressure was 24 mm Hg in both eyes, and slit- lamp biomicroscopy and indirect ophthalmoscopy were normal. A diagnosis of acute bilateral retrobulbar optic neuritis was made, and the patient was hospitalized for therapy with i. v. methylprednisolone, 250 mg every 6 h. MRI scan of the head and orbits with and without gadolinium was repeated 1 day after initiation of treatment (- 15 days after onset of symptoms) using a fat- saturation- suppression technique; there was gadolinium enhancement of both optic nerves in the intracranial portion of their prechias-mal course in a pattern consistent with acute bilateral optic neuritis ( Fig. 1). There was no signal enhancement in the optic chiasm ( Fig. 2). The MRI scans from the outside hospital ( done during the first week of disease) were then obtained; they were found to demonstrate gadolinium enhancement of the body of the chiasm ( Fig. 3). During hospitalization, visual function did not change. Following a 3- day course of therapy ( 12 i. v. doses of methylprednisolone), the patient was discharged on an oral dose of 1 mg/ kg body weight of prednisone, which was used for 10 days following discharge. Six weeks following discharge, her visual acuity had improved to 20/ 60 OD and 20/ 40 OS. Visual fields had recovered to the extent that there were bilateral relative central scotomas with complete recovery of peripheral field beyond 30° of eccentricity in both eyes. Ten weeks postdis-charge, the patient's ophthalmologist reported acuities of 20/ 40 in each eye. Four and a half months following discharge, the patient felt that visual function had not changed any further. Visual fields showed some further improvement, however, with loss of the well- defined relative central scotomas. There persisted generalized depression of the central visual field in both eyes by Goldmann perimetry ( though the central scotomas had resolved); color vision was very poor ( 1- 3 of 17 Ishihara pseudoisochromatic plates with either eye); and both optic discs were diffusely atrophic. DISCUSSION A case of bilateral retrobulbar optic neuritis with profound visual loss is described. An MRI done during the first week following onset of visual loss had been interpreted as normal; however, on review it was seen to demonstrate a chiasmal lesion marked by signal enhancement with i. v. gadolinium. A repeat MRI some 15 days following symptom onset demonstrated centrifugal migration of the signal enhancement into the proximal portions of both optic nerves just anterior to the chiasm, while the body of the chiasm no longer enhanced. Little is known about the acute evolution of demyelinating lesions in optic neuritis. In studies of patients with demyelinating disease, disruption of the blood- brain barrier, as demonstrated by gadolinium enhancement on MRI, occurs at the onset of disease and is thought to be the initial pathologic event in the demyelinating plaques of MS ( 8- 12). The resulting leakage of fluid may produce a neural conduction block and may be the responsible pathophysiological mechanism for the initial clini- / Neuro- Ophthalmol, Vol. 16, No. 1, 1996 BILATERAL OPTIC NEURITIS 11 FIG. 1. MRI study 2 weeks after onset of symptoms: axial view, T1- weighted image. Small arrows indicate proximal optic nerves just anterior to chiasm. A: Without enhancement. B: With gadolinium enhancement and fat- saturation suppression. Enhancement can be seen in both optic nerves anterior to the optic chiasm. FIG. 2. From the same study as shown in Fig. 1: coronal view, T1- weighted image. A: Without enhancement. B: With gadolinium enhancement and fat- saturation suppression. There is no enhancement evident in the optic chiasm ( arrows). J Neuro- Ophthalmol, Vol. 16, No. 1, 1996 12 J. B. SOLTAU AND W. M. HART, JR. FIG. 3. Initial MRI study, obtained during first week of disease. A: Axial view, T1- weighted image without enhancement. B: Axial view, T1- weighted image with gadolinium enhancement. The enhanced lesion can be seen within the optic chiasm ( arrows). C: Coronal view, T1- weighted image with gadolinium enhancement. The enhanced lesion can be seen within the optic chiasm ( arrows). cal neurological deficits ( 13). Prior to the advent of gadolinium enhancement in MRI studies, the acute changes of demyelinating disease were more difficult to observe. The acute and subacute changes in the MRI appearance of demyelinating lesions as detected by gadolinium enhancement have been described as initial enlargement followed by subsequent retraction in size, often without concomitant change in neurologic deficits ( 17). With the now common use of gadolinium enhancement, the acute changes caused by the breakdown of the blood- brain barrier are more readily detectable. The use of fat- saturation- suppression signal- processing techniques also improves the chances of detecting early disease in the optic nerves. The changing pattern in our case differs from prior descriptions in that a propagated wave of gadolinium enhancement appears to have / Neuro- Ophthalmol, Vol. 16, No. 1, 1996 BILATERAL OPTIC NEURITIS 13 migrated from an initial focus in the chiasm, leaving behind a central nidus of nonenhancing tissue. The findings of the second scan closely resemble the appearance of case 1 in the report by Guy et al. ( 6). It is quite likely that similar patterns of bilateral symmetrical disease of the posterior optic nerves often arise from single focal lesions originating in the chiasm. In guinea pigs with experimental allergic encephalomyelitis, evolving lesions have been demonstrated by fat- suppression MRI and gadolinium enhancement, starting at the anterior end of the optic nerve and progressing toward the orbital apex ( 14). Changes in the patterns of CNS demy-elinating lesions in patients with MS have been studied extensively ( 15- 17), but the acute topographical progression of a single demyelinating focus within the afferent visual system has not been described. We present MRI findings documenting the centrifugal migration of a gadolinium-enhanced lesion from the chiasm into the proximal optic nerves, much like a propagated wave of disturbance. This would seem to account for the otherwise unexpected tendency for bilaterally symmetrical demyelination to occur in the retrobulbar optic nerves. The results of an optic neuritis treatment trial showed that, in patients with optic neuritis treated with high- dose i. v. corticosteroids within 8 days of initial symptoms, the recovery of visual acuity is accelerated ( 18,19). Because of our patient's profound visual loss, we elected to treat her with i. v. methylprednisolone, hoping to minimize the period of her profound visual disability as much as possible. Finally, it may seem odd that a chiasmal lesion would not be associated with a heteronymous ( bitemporal) hemianopia and that the visual field defects did not seem to respect the vertical meridian. In the acute stages of the disease the degree of dysfunction was so profound that no recordable visual field could be detected in either eye. This suggests that the disease affected a broad cross-section of the chiasm and posterior optic nerves, including both crossing and noncrossing fibers to an equal extent, so that the pattern ordinarily seen with chiasmal disease was erased. 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