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Show Journal of Neuro- Ophthalmology 17( 4): 226- 230, 1997. © 1997 Lippincott- Raven Publishers, Philadelphia Congenital Optic Tract Syndrome: Magnetic Resonance Imaging and Scanning Laser Ophthalmoscopy Findings Marjorie A. Murphy, M. D.,* David H. Grosof, Ph. D. and William M. Hart, Jr., M. D., Ph. D. Summary: Lesions of the optic tract produce a distinctive pattern of optic atrophy and visual field loss and may be due to either congenital or acquired causes. We report a case of a congenital optic tract syndrome and correlate the magnetic resonance imaging findings with the appearance of nerve fiber layer defects found by confocal scanning laser ophthalmoscopy. Key Words: Optic tract syndrome- Magnetic resonance imaging- Scanning laser ophthalmoscopy. Lesions of the optic tract produce a distinctive pattern of optic atrophy and visual field loss and may be due to either congenital or acquired causes. Previous reports have documented the funduscopic appearance of the disk changes as recorded by conventional fundus photography ( 1), and there are a few reports of the radiologic findings of lesions primarily involving the optic tracts using high- resolution neuroimaging techniques ( 2,3). We report a case of a congenital optic tract syndrome and correlate the magnetic resonance imaging ( MRI) findings with the appearance of nerve fiber layer defects found by confocal scanning laser ophthalmoscopy ( SLO). CASE REPORT A 30- year- old woman was referred to our institution by an optometrist for a left homonymous hemianopia noted on a screening visual field examination. She had initially seen the optometrist for a routine examination for contact lenses and denied any visual disturbance. Her past medical history was unremarkable and she was on no medications. Her past ocular history was notable for a Manuscript received June 10, 1996; accepted June 25, 1997. From the Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, Missouri, U. S. A. * M. A. M. is also affiliated with the Department of Ophthalmology, Rhode Island Hospital, Brown University School of Medicine, Providence, Rhode Island, U. S. A. Address correspondence and reprint requests to Dr. William M. Hart, Jr., Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, Box 8096, 660 S. Euclid Ave, St. Louis, MO, 63110- 1093, U. S. A. history of amblyopia in the right eye, and she had worn glasses since 18 months of age. On examination, best corrected visual acuity was 20/ 60 in the right eye and 20/ 20 in the left eye. Manifest refraction was + 1.00 in both eyes, and extraocular motility was normal. Pupils were 4 mm and reactive to light without an afferent pupillary defect. One of 16 Ishihara color plates was correctly identified in the right eye and two of 16 was correctly identified in the left eye. Threshold static perimetry ( Fig. 1) showed an incongruous left homonymous hemianopia. Cranial nerves III- XII were intact. Slit- lamp examination was normal, and tensions were 14 mm Hg in both eyes. A dilated fundus examination ( Fig. 2) showed temporal disk pallor in the right eye and bow- tie atrophy in the left eye with evidence of a double ring sign in both eyes. Confocal scanning laser ophthalmoscopy of the nerve fiber layer in the right eye ( Fig. 3) showed loss of striations in an arcuate distribution temporally with intact nasal fibers of the papillo-macular bundle. Scanning laser ophthalmoscopy of the nerve fiber layer in the left eye ( Fig. 3) showed loss of striations of the nasal papillomacular bundle while the temporal arcuate fibers were intact. An MRI of the brain and orbits with gadolinium enhancement ( Fig. 4) showed enlargement and increased signal intensity of the right cerebral peduncle and an adjacent arachnoid cyst. The lesion gave the appearance of producing a mass effect with involvement of the right optic tract and did not enhance after contrast administration. It was felt to represent either a low- grade glioma or possibly a brain- stem hamartoma. The right occipital lobe was also significantly smaller than the left. The optic nerves and chiasm were normal. The patient remained asymptomatic at 4 months' follow- up. DISCUSSION Based on the history and clinical data, our patient's case likely represents a congenital optic tract syndrome. She was asymptomatic at the time of the initial screening visual field and still remains unaware of a visual field defect. One can speculate that the diagnosis of amblyopia at 18 months of age may in fact have been a decrease in vision secondary to involvement of the optic chiasm and/ or nerve by the gliomatous or hamartomatous process. This may then have arrested in growth with subsequent involution, leaving only a mild resultant decrease in acu- 226 CONGENITAL OPTIC TRACT SYNDROME 227 r t H f K i L I D - .= T n f e < : r i 4 L b I C CT " ili^ 1M- n m i U P *•€• » * WC " » III *( « i( iiw am • ' » ' » "''•> T H P* B a MOh_ D T r - t T * . tHl* iF|( 01- 11-*' ZAIt LD- tt- W mvmp to d i t l t t l H l l 4 1M Humphrey vlfiiiel fislri 3TJ- P clemnnstralrrg an incongruous laft homonymous hemianopia. ity. The appearance of the disks, which display both mild hypoplasia and a double ring sign,. suggest a congenital or infantile onset of the disturbance. The smaller occipital lobe on the side of the- tract lesion lends further support to an early onset of the mass causing the tract lesion. Although lesions involving primarily the optic tract are recognized infrequently ( 4,5), their clinical characteristics have been well described ( 1,2,4- 8). The visual field defect is a homonymous hemianopia that is most often partial but may be complete. When the defect is partial, it is often highly incongruous ( 4- 6). When it is complete, there is an associated contralateral APD ( 6) due to the greater number of decussating fibers in the chiasm. However, an ipsilateral APD may be noted in patients with ipsilateral acuity loss due to simultaneous involvement of the lateral bar of the chiasm and/ or ipsilateral optic nerve. The latter condition has been termed a " posterior junction syndrome," characterized by an incongruous hemianopia associated with decreased acuity ipsilateral to the optic tract lesion ( 5). When the hemianopia is incomplete and visual acuity is normal, no APD may be present. Hence, depending on the extent of involvement of the optic tract and adjacent visual pathways structures, there may be an ipsilateral APD, contralateral APD, or none at all. In our patient's case, the absence of an APD may be due to a balance between involvement of the ipsilateral optic nerve and the contralateral decussated fibers of the optic tract. Acuity and color discrimination are said to be preserved in the optic tract syndrome, unless there is bilateral involvement or anterior extension to involve the optic nerve or chiasm ( 6). Our patient's poor color vision F7G. 2. Funaus examination snowing temporal disk pallor in the right eye ( left) and bow- tie atrophy in the left eye ( right) with evidence of a double ring sign in both eyes. J Neuro- Ophthalmol, Vol. 17, No. 4, 1997 FIG. 3. Scanning laser ophthalmoscope images at the level of the nerve fiber layer. Top left: Reference photo of the right eye obtained with infrared light at 790 nm and a small fraction of visible light at 633 nm to render the fixation cross, which marks the fovea. Black and white boxes mark the location of the middle and lower left figures, respectively. Middle left: Close- up view of the right eye obtained with infrared light showing intact nasal macular nerve fiber striations { arrows), with loss of contrast in the region of the temporal arcuate fibers. Bottom left: Close- up view of the right eye obtained with infrared light showing intact nasal macular fiber striations ( black arrows), with drop- off in nerve fiber layer striations temporal to the fovea ( white arrow). Top right: Reference photo of the left eye obtained with infrared light at 790 nm and a small fraction of visible light at 633 nm for the fixation cross, which marks the fovea. White and black boxes mark the location of the images in the middle and lower left, respectively. Middle right: Close- up view of the left eye obtained with infrared and argon blue light showing intact temporal nerve fiber striations ( black arrows), with loss of contrast in the region of the nasal macular fibers. The white arrow marks the fovea. Bottom right: Close- up view of the left eye obtained with infrared and argon blue light showing the intact temporal fibers arcing around the fovea ( arrows), again with loss of contrast in the region of the nasal macular fibers. J Neuro- Ophthalmol, Vol. 17, No. 4, 1997 CONGENITAL OPTIC TRACT SYNDROME 229 in- wv- IWi HUGE K ilUB J F ] . in ii • B j ° f < * l II i \ | > L Jk i y ^ ^ j "• _ JL t J flfj L \ jHNAb BsAET1: WR lay mchLwn visir i : r H| FIG. 4. Axial proton density MRI ( top left) and T2- weighted MRI ( top right) showing enlargement and increased signal intensity of the right cerebral peduncle ( large arrow) and an adjacent arachnoid cyst ( small arrow). Note also that the right occipital lobe is smaller than the left. Coronal T1 - weighted image ( bottom left) demonstrating inferior displacement of the right optic tract ( left arrow) and a normal left optic tract ( right arrow). Axial T1- weighted image ( bottom right) shows no enhancement after contrast administration ( left arrow). The arachnoid cyst ( white arrowhead) and the normal left optic tract ( right arrow) are again noted. The right optic tract is out of the plane of section due to its inferior displacement. The lesion likely represents either a low- grade glioma or a hamartoma and produces a mass effect with involvement of the right optic tract. suggests bilateral disease. As with our case, patients with congenital homonymous hemianopia are often unaware of any defect in their visual fields ( 2,9), although not always ( 3). Congenital lesions of the cerebral hemisphere may involve the optic tract primarily or trans-synaptically ( 1,7,9). Lesions involving the optic tract directly range from neoplasms to unilateral aplasia of the optic tract ( 2,3,10). Acquired lesions are most often symptomatic, with blurred vision being the most common initial manifestation in one series ( 4), and etiologies range from neoplasms to aneurysms. Patients with either congenital or acquired optic tract lesions may or may not have an associated neurologic deficit. A characteristic pattern of optic atrophy is noted in both congenital and acquired cases of the optic tract syndrome ( 1,4- 6,9). In acquired cases, the ipsilateral disk shows temporal pallor, whereas the contralateral disk shows band or bow- tie atrophy, reflecting loss of both J Neuro- Ophthalmol, Vol. 17, No. 4, 1997 230 M. A. MURPHY ETAL. the nasal macular and peripheral fibers. In congenital cases, the fundus appearance has been termed ' ' homonymous hemianoptic hypoplasia" by Hoyt et al. ( 1). The disks also appear small with double- contoured margins, a sign suggesting retrograde rather than embryogenic hypoplasia of optic axons. The contralateral disk has a reduced horizontal diameter reflecting hypoplasia of the mid- zone. Although the clinical characteristics of the optic tract syndrome have been well described, most reports were written before the widespread use of modern high-resolution neuroimaging techniques. Three cases of congenital homonymous hemianopia due to aplasia of the optic tract noted on MRI have been reported ( 3). Our patient's optic tract lesion may represent either compression by a hamartoma or an involuted glioma of the visual pathways. Gliomas of the anterior pathways characteristically show early growth followed by stability in many patients, although they have the potential to invade the brain ( 8). Although the funduscopic features of the optic tract syndrome have been described by conventional fundus photography in standard and red- free illumination ( 8), we believe this to be the first report of the use of scanning laser ophthalmoscopy to describe the pattern of nerve fiber layer atrophy in an optic tract syndrome. Scanning laser ophthalmoscopy provides a high- contrast video image of the retina using relatively low levels of illumination that are both safe and comfortable for the patient ( 11- 16). A laser beam scans across the retina, and energy returned from this moving spot is detected and synchronously decoded to construct a video image of the fundus point by point. The confocal SLO yields images of unusually high contrast due to the reduction of scattered light and allows specific layers of the retina to be studied ( 14,17). Assessment of nerve fiber layer defects in ocular hypertension and glaucoma by scanning laser ophthalmoscopy has recently been shown to yield a high degree of intra- and interobserver reproducibility ( 15). Normal nerve fibers look like compact reflective lines that follow a ' ' race- track'' pattern around the fovea, and the temporal horizontal raphe is strikingly shown. Nerve fiber layer defects can be clearly identified in all areas including the papillomacular bundle, which is generally quite difficult to image by conventional fundus photography. Our patient clearly demonstrates loss of temporal fibers ipsilateral to the tract lesion and loss of nasal fibers contralateral to the lesion. CONCLUSION We report on a patient with a congenital optic tract syndrome and discuss the MRI and SLO findings. The evolution of these high- resolution imaging techniques continues to enhance our understanding of this and many other disease entities. Acknowledgment: This study was supported in part by National Institutes of Health Core Grant for Vision Research EY 02687, Research to Prevent Blindness, Inc., and The J. Epstein Foundation ( Dr. Grosof). REFERENCES 1. Hoyt WF, Rios- Montenegro EN, Behrens MM, Ecklehoff RJ. Homonymous hemioptic hypoplasia: fundoscopic features in standard and red- free illumination in three patients with congenital hemiplegia. Br J Ophthalmol 1972; 56: 537- 45. 2. Margo CE, Hamed LM, McCarty J. Congenital optic tract syndrome. Arch Ophthalmol 1991; 109: 1120- 2. 3. El Gammel T, Brooks B, Harbour R, Kline L, Jacob P. MR of uncommon congenital and vascular lesions of the intracranial pathways. Neuroradiology 1990; 32: 488- 91. 4. Bender MR, Bodis- Wollner I. Visual dysfunction in optic tract lesions. Ann Neurol 1978; 3: 187- 93. 5. Savino PJ, Paris M, Schatz NJ, Orr LS, Corbett JJ. Optic tract syndrome: a review of 21 patients. Arch Ophthalmol 1978; 96: 656- 63. 6. Newman SA, Miller NR. 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