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Show PHOTO ESSAY Loss of Myelinated Retinal Nerve Fibers From Chronic Papilledema Milan Shah, MD, Hee-Jung Park, MD, Ali Reza Gohari, MD, and M. Tariq Bhatti, MD FIG. 1. A. On the first postoperative day after resection of a suprasellar mass there is chronic optic disc edema (papilledema) of both optic discs andmyelinated nerve fibers in the left eye. B. Two months postoperatively, both optic discs have become pale and the myelinated nerve fibers appear thinner. C. Thirty months postoperatively, the optic discs are still pale, and the myelinated nerve fibers have disappeared along with development of atrophy of the nerve fiber layer. Department of Ophthalmology (SM, H-JP, ARG), University of Florida, College of Medicine, Gainesville, Florida; and Departments of Ophthalmology and Medicine, Division of Neurology, (MTB), Duke University Eye Center, Duke University Medical Center, Durham, North Carolina. Address correspondence to M. Tariq Bhatti, MD, 2351 Erwin Road, Duke University Eye Center, DUMC Box 3802, Durham, NC 27710; E-mail: tariq. bhatti@duke.edu J Neuro-Ophthalmol, Vol. 28, No. 3, 2008 219 Abstract: An intracranial pilocytic astrocytoma was diagnosed in a 13-year-old boy after he presented with headaches and visual disturbances. The initial ophthalmoscopic examination revealed papilledema bilaterally and myelinated retinal nerve fibers (MRNFs) in the left eye. Serial ophthalmoscopic examinations demonstrated gradual fading of the MRNFs beginning 2 months after tumor resection and their complete disappearance by 2 years after surgery. The disappearance of MRNFs has been described in the presence of ischemia, compression, glaucoma, and demyelinating disease of the optic nerve. This patient demonstrates that loss of myelinated nerves fibers may also occur with the optic atrophy that may follow chronic papilledema. (J Neuro-Ophthalmol 2008;28:219-221) A13-year-old boy presented with a 3-day history of headache, nausea, and visual disturbance. MRI revealed a heterogeneous suprasellar mass originating from the anterior hypothalamus and massive hydrocephalus. A craniotomy with subtotal excision was performed, and the mass was confirmed to be a juvenile pilocytic astrocytoma. On the first postoperative day, visual acuity was 20/100 in the right eye and 20/400 in the left eye. He could not identify any of the Ishihara pseudochromatic plates. The pupils were sluggishly reactive to light with a subtle left relative afferent pupillary defect. Goldmann perimetry revealed severely constricted visual fields with 5 central islands in both eyes. Indirect ophthalmoscopy revealed bilateral optic edema with mild pallor. Extensive myelinated retinal nerve fibers (MRNFs) continuous with the optic disc were present in the patient's left eye (Fig. 1A). On reexamination 2 months after surgery, visual acuity was hand motions in both eyes. Ophthalmoscopy revealed optic nerve pallor in both eyes. The myelination of the retinal nerve fibers in the left eye had become less dense with enhanced visibility of the retinal vasculature (Fig. 1B). On reexamination 30 months after surgery, visual acuity had improved to 20/400 in the right eye and 20/200 in the left eye. Ophthalmoscopy now showed complete disappearance of the MRNFs and entire visibility of the previously obscured retinal vasculature (Fig. 1C). MRNFs are usually an asymptomatic developmental anomaly and most often are detected incidentally on routine examination. They appear ophthalmoscopically as gray-white striations with frayed margins that follow the dis-tribution of an underlying wedge of axons (1). These pathologic and anatomic features of MRNFs were first elucidated by Virchow in 1856 (1). The normal retina is devoid of oligodendrocytes and its constituent bundles of lipoprotein lamellae known as myelin (1,2). The presence of MRNFs therefore highlights an anomaly in the development of the anterior visual path-way. In the normal course of development,myelination of the pregeniculate pathway commences in the lateral geniculate body at 5 months of gestation, tracking anteriorly to ter-minate at the lamina cribrosa around the time of birth (3). In some individuals, myelination may extend anterior to the lamina cribrosa to involve the optic nerve head or retina. In studying 3968 consecutive autopsy cases, Straats-ma et al (1) determined the prevalence of MRNFs to be 0.98%. Histologic examination has shown that the un-derlying retina in MRNFs usually does not exhibit any pigmentary, vascular, or associated morphologic abnor-malities, although microcystoid degeneration of the nerve fiber layer has been noted. Although usually presenting as congenital and stationary lesions, MRNFs have been rarely described as being acquired or progressive (4). They can be associated with many other ocular and systemic abnor-malities, including neurofibromatosis, keratoconus, colo-boma, polycoria, and craniofacial dysostosis (5). Despite the existence of multiple theories, the exact pathogenesis of MRNFs remains to be elucidated. Based on the observation that animals with a poorly developed lamina cribrosa have frequent myelination of the retina, one proposal is that there may be a physical defect in the lamina itself (5). Another postulate is that oligodendrocytes are anomalously located in the retina, resulting in aberrant myelination (1). Recent results in experimental neurobiol-ogy, however, suggest that soluble proteins in the retina play an integral role in both the migration and differentiation of oligodendrocyte precursors (2). Thus, myelination may be the result of a failure in an inhibitory chemical signal rather than a physical defect in the lamina itself. Optic atrophy due to trauma, ischemia, compression, or inflammation can result in loss of ganglion cell axons and their respective myelin sheaths (3). Loss of MRNFs has been reported in association with anterior ischemic optic neuropathy, syphilis, pituitary tumor, glaucoma, central retinal artery occlusion, plaque radiotherapy, Leber hered-itary optic neuropathy, and pars plana vitrectomy (1,3,6,7). The mechanism common to the loss of myelin in the above cases is neuronolytic degeneration, in which myelin breakdown is due to atrophy of ganglion cell axons. Loss of retinal myelin has also been shown in the presence of demyelinating inflammatory optic neuritis, for which periaxial degeneration remains the probable mechanism, with demyelination being the primary event and axonal loss following secondarily (3). Although atrophy and loss of the retinal nerve fibers is often a subtle ophthalmoscopic finding, our patient dramat-ically highlights the extent of nerve fiber layer damage by 220 q 2008 Lippincott Williams & Wilkins J Neuro-Ophthalmol, Vol. 28, No. 3, 2008 Shah et al demonstrating complete disappearance of extensive intraocular myelin. It is well recognized that secondary optic atrophy can ensue after chronic papilledema. In our patient, the loss of myelination is postulated to occur via neuronolytic degen-eration consequent to atrophy of ganglion cell axons from a sustained increase in intracranial pressure. To the best of our knowledge, this is the first patient in whom loss of MRNFs due to chronic papilledema has been photographically documented. REFERENCES 1. Straatsma BR, Foos BY, Heckenlively JR, et al. Myelinated retinal nerve fibers. Am J Ophthalmol 1981;91:25-38. 2. Gao L, Macklin W, Gerson J, et al. Intrinsic and extrinsic inhibition of oligodendrocyte development by rat retina. Dev. Biol 2006;290: 277-86. 3. Schachat AP, Miller NR. Atrophy of myelinated retinal nerve fibers after acute optic neuropathy. Am J Ophthalmol 1981;92:854-6. 4. Jean-Louis G, Katz BJ, Digre KB, et al. Acquired and progressive retinal nerve fiber layer myelination in an adolescent. Am J Ophthalmol 2000;130:361-2. 5. Lee MS, Gonzalez C. Unilateral peripapillary myelinated retinal nerve fibers associated with strabismus, amblyopia, and myopia. Am J Ophthalmol 1998;125:554-6. 6. Williams AJ, Fekrat S. Disappearance of myelinated retinal nerve fibers after pars plana vitrectomy. Am J Ophthalmol 2006; 142:521-3. 7. Gicquel JJ, Salama B, Mercie M, et al. Myelinated retinal nerve fibers loss in Leber's hereditary optic neuropathy. Acta Ophthalmol Scand 2005; 83:517-8. 221 Myelinated Retinal Nerve Fibers J Neuro-Ophthalmol, Vol. 28, No. 3, 2008 |
