| OCR Text |
Show ORIGINAL CONTRIBUTION Isolated Cortical Visual Loss With Subtle Brain MRI Abnormalities in a Case of Hypoxic- ischemic Encephalopathy Edward Margolin, MD, Sachin K. Gujar, MD, and Jonathan D. Trobe, MD Abstract: A 16- year- old boy who was briefly asystolic and hypotensive after a motor vehicle accident complained of abnormal vision after recovering consciousness. Visual acuity was normal, but visual fields were severely constricted without clear hemi-anopic features. The ophthalmic examination was otherwise normal. Brain MRI performed 11 days after the accident showed no pertinent abnormalities. At 6 months after the event, brain MRI demonstrated brain volume loss in the primary visual cortex and no other abnormalities. One year later, visual fields remained severely constricted; neurologic examination, including formal neuropsychometric testing, was normal. This case emphasizes the fact that hypoxic- ischemic encephalopathy ( HIE) may cause enduring damage limited to primary visual cortex and that the MRI abnormalities may be subtle. These phenomena should be recognized in the management of patients with HIE. (/ Neuro- Ophthalmol 2007; 27: 292- 296) n hypoxic- ischemic encephalopathy ( HIE) in adults, clinical deficits and imaging abnormalities typically reflect damage to the neocortex, deep cerebral gray nuclei, hippocampus, cerebellum, and parieto- occipital watershed regions ( 1- 6). We describe a 16- year- old boy who was resuscitated after becoming asystolic and hypotensive following a motor vehicle accident. He recovered all neurologic function except for severely constricted visual fields. Brain MRI performed within 2 weeks of the event did not disclose any pertinent abnormalities. Five months after the event, MRI showed relatively subtle atrophy limited to the medial occipital region. This case is presented From the Departments of Ophthalmology and Visual Sciences ( Kellogg Eye Center) ( EM, JDT) Neurology, ( JDT) and Radiology ( Neuroradiology) ( SKG), University of Michigan, Ann Arbor, Michigan. Address correspondence to Jonathan D. Trobe, MD, Kellogg Eye Center 1000 Wall St., Ann Arbor, MI 48109; E- mail: jdtrobe@ umich. edu to emphasize the fact that HIE may cause isolated yet profound cortical visual loss without obvious correlative MRI abnormalities. CASE REPORT A 16- year- old boy was an unrestrained driver of a car that collided with a tree at an unknown speed. Emergency rescue required 40 minutes to extricate him from the vehicle. He was unresponsive at the scene and was promptly intubated, after which he suffered a 5- minute period of asystole. Pulse and blood pressure were recovered with resuscitation, including the use of atropine and epinephrine. Upon arrival at our hospital, he was unresponsive. A bilateral pneumothorax, thigh burn, multiple rib fractures, and a Tl vertebral fracture were found. A head CT scan on the day of arrival was normal. Upon extubation 5 days later, he was alert but disoriented to time and amnestic for the accident yet able to recall events preceding it. He immediately reported that he could not see. A bedside ophthalmologic examination disclosed that visual acuity was hand movements in both eyes. Pupillary examination was normal, extraocular movements were full on command, and he was orthophoria Ophthalmoscopic examination was normal in both eyes. On the second day after extubation, results of bedside mental status testing were normal, and he could remember the accident. Brain MRI performed 11 days after the accident (" first MRI") demonstrated mildly increased curvilinear T2/ FLAIR signal along the lateral margins of the posterior portions of the lentiform nuclei on both sides, not associated with restricted diffusion ( Fig. 1A- D). There was subtle high T2/ FLAIR signal and restricted diffusion in the splenium of the corpus callosum. There were small foci of enhancement within the posterior parietal subcortical white matter and centrum semiovale attributed to shear injury, and a small focus of curvilinear gyral enhancement posteriorly at the right occipital pole ( Fig. 1E- F) which was attributed to trauma. These findings did not provide an adequate explanation for the patient's poor vision. 292 J Neuro- Ophthalmol, Vol. 27, No. 4, 2007 Cortical Visual Loss J Neuro- Ophthalmol, Vol. 27, No. 4, 2007 F^ ri) 1 W f l^ B '£ FIG. 1. Brain MRI performed on day 11 after the accident (" first MRI"). Axial FLAIR ( A), Fast spin echo ( FSE) T2 ( B), diffusion ( C), and ADC map ( D) at the level of the basal ganglia. Postcontrast sagittal image ( E), andTI coronal image ( F). There is high FLAIR and T2 signal along the lateral aspects of the posterior lentiform nuclei { small arrow, A, B). There is minimally increased FLAIR signal in the medial occipital lobes, more on the right { large arrow, A). The diffusion image ( C) and ADC map ( D) are normal. There is focal cortical gyriform enhancement in the right occipital lobe { large arrow, E), and several punctuate foci of enhancement in the centrum semiovale and subcortical left parietal white matter { small arrows, E, F). Three weeks after the accident, he was discharged with impaired mobility due to right acetabular and left ulnar fractures as well as a healing right thigh skin graft. Before discharge he had undergone formal psychometric testing that revealed tactile perceptual and spatial reasoning abilities within normal limits. Six weeks after the accident, repeat psychometric testing revealed normal attention and high average scores on memory and learning. Twelve weeks after the accident, he reported that his vision was not normal. Ophthalmologic examination disclosed visual acuities of 20/ 20 in both eyes. The remainder of the examination was normal except for severely constricted Humphrey visual fields with mean deviations ( MDs) of 26.8 dB for the right eye and 22.8 dB for the left eye without a hemianopic pattern ( Fig. 2). Goldmann visual fields were also constricted without clear localizing features. He had no difficulty recognizing objects, familiar, or famous faces, counting objects in an array, localizing objects in space, or interpreting action photographs. Twenty- four weeks after the accident, visual acuity was 20/ 15 in both eyes, but visual fields remained severely constricted with stable MDs of 28 dB for the right eye and 28 dB for the left eye with the same pattern as noted previously ( Fig. 3). A repeat MRI performed 24 weeks after the accident (" second MRI") was reported as showing resolution of previously noted signal abnormalities and enhancement. Because of the persisting profound visual field defects, 293 J Neuro- Ophthalmol, Vol. 27, No. 4, 2007 Margolin et al FIG. 2. Humphrey 24- 2 visual fields performed 2 months after the episode of cardiogenic hypoxia and hypotension show markedly high thresholds in all quadrants without clear hemianopic features. Visual acuity was 20/ 15 in both eyes. a review of the second MRI study was conducted. It was reinterpreted as showing volume loss of the medial occipital lobes, including the area of the primary visual cortex, without signal abnormalities on the FLAIR images ( Fig. 4). The first MRI ( Fig. 1) was also reviewed and reinterpreted as showing increased FLAIR signal in the occipital cortex. The subtle area of occipital gyriform enhancement was reinterpreted as indicating a subacute ischemic lesion. FIG. 3. Visual fields performed 3 months after the episode of cardiogenic hypoxia and hypotension show little change relative to those of Fig. 2. FIG. 4 . Axial FLAIR MRI performed 6 months after the study in Fig. 1. It demonstrates loss of volume in the occipital lobes with prominent medial occipital sulci ( arrows). One year after the accident, visual acuity remained 20/ 15 in both eyes, and visual fields were slightly improved at MDs of 23 dB for the right eye and 17.8 dB for the left eye ( Fig. 5). Goldmann visual fields showed enough breadth to permit legal driving in the state of Michigan. DISCUSSION Our patient is notable for having developed profound and persistent hypoxic- ischemic damage to the primary visual cortex without other enduring neurologic deficits. Recognition of this phenomenon was delayed because the visual field lacked the typical hemianopic features associated with visual cortical damage, and the MRI signs were so subtle- on the early and the late studies- as to be initially overlooked. We attribute that error in part to the fact that the primary visual cortex is not widely recognized as an isolated target in HIE. If hypoxia is the main insult, the thalamus ( including lateral geniculate body), hippocampus, globus pallidus, and deep cerebellar nuclei are described as experiencing the greatest damage ( 5). If hypoperfusion is the main insult, as in the cardiac arrest of our patient, damage is said to occur predominantly in the watershed areas ( arterial border 294 © 2007 Lippincott Williams & Wilkins Cortical Visual Loss J Neuro- Ophthalmol, Vol. 27, No. 4, 2007 FIG. 5. Visual fields performed 1 year after the episode of cardiogenic hypoxia and hypotension show minimal improvement relative to earlier fields. zones) ( 5,7,8). In adults, these regions include the cerebral and cerebellar cortex, the hippocampus, and the basal ganglia ( 1,7,9,10). In preterm infants, it is the periventricular white matter ( 11- 14). The posterior cerebral watershed zone involves the parieto- occipital region. Ischemia to this region produces the visual spatial and ocular motor deficits of the Balint- Holmes syndrome ( 9,15,16). In our patient, there were no features of this syndrome. In previous clinical descriptions of the visual consequences of HIE, homonymous hemia-nopia has been described, but always in combination with features of the Balint- Holmes syndrome ( 15). The reported MRI abnormalities in adult HIE have been associated with the cerebral and the cerebellar gray matter, particularly the large cell layers of the neocortex and Purkinje cells of the cerebellar cortex, along with the hippocampus, basal ganglia, and thalami ( 1- 6,7,11,17). In the hyperacute period after the ischemic event (< 24 hours after the insult), MRI signal abnormalities have been found on diffusion- weighted imaging ( DWI) in the cerebellum, basal ganglia, and cerebral cortex ( 1,17). Later in the acute and the early subacute period ( 24 hours- 14 days), abnormal signal is also demonstrable on the T2 and FLAIR sequences. In one report, changes on DWI were prominent in the white matter in the early subacute period, representing post-hypoxic demyelination ( 3). On Tl images, cerebral swelling and obscuration of gray- white matter differentiation has been described ( 4,17). Diffusion abnormalities after focal ischemia tend to peak at 2- 3 days after the event and tend to fade by 10- 12 days. Enhancement after contrast administration is often demonstrated in the subacute period and may persist for several weeks. In the late subacute period ( 14- 20 days) and in the chronic period (> 20 days), conventional MRI shows signs of laminar necrosis ( 1,2,18,19) and volume loss. Our patient had no substantial MRI abnormalities 11 days after the HIE event and volume loss limited to the medial occipital region 6 months later. Only one previous report has described MRI changes in the visual cortex after hypoxic injury due to respiratory arrest after a motor vehicle accident ( 20). There was high Tl signal 1 month after the injury and high T2 signal in the same area 4 months after the accident. DWI was not performed. The patient reportedly had a bilateral visual disturbance that persisted on a 6- month follow- up. This disturbance was attributed to " cortical blindness" but not further delineated. Interestingly, hypoglycemia in the neonate has also been reported to have a propensity for occipital distribution of MRI changes. Unlike the watershed pattern seen in neonatal HIE, neonatal hypoglycemia shows occipital MRI abnormalities in up to 82% of cases, with half of these infants sustaining visual impairment ( 21- 25). In adult posthypoglycemic coma, MRI changes variably involve the hippocampus, basal ganglia, and the cerebral cortex without mention of an occipital lobe predilection ( 26,27). Laminar necrosis is common pathologic finding ( 28) in these patients. Although not traditionally acknowledged as a vulnerable region in HIE, the primary visual cortex has features that could make it susceptible to damage in this condition. It lies at a remote region of arterial blood supply, the terminus of the posterior cerebral artery. Under hypotensive conditions, perfusion may not be adequate. The dual arterial supply of the occipital tip from posterior and middle cerebral arteries may account for preservation of the central visual field, including visual acuity. The topographic role of the primary visual cortex precludes any reduplication of neurologic function. That is, each point in visual space is represented in only one tiny cortical region. In case of damage, ischemic or otherwise, there is no back- up. REFERENCES 1. Kandiah P, Ortega S, Torbey T. Biomarkers and neuroimaging of brain injury after cardiac arrest. Semin Neurol 2006; 26: 413- 21. 2. Arbelaez A, Castillo M, Mukherji SK. Diffusion- weighted MR imaging of global cerebral anoxia. AJNR Am JNeuroradiol 1999; 20: 999- 1007. 3. Chalela JA, Wolf RL, Maldjian JA, et al. MRI identification of early white matter injury in anoxic- ischemic encephalopathy. Neurology 2001; 56: 481- 5. 4. Wijdicks EF, Campeau NG, Miller GM. MR imaging in comatose survivors of cardiac resuscitation. AJNR Am J Neuroradiol 2001; 22: 1561- 5. 5. Singhal AB, Topcuoglu MA, Koroshetz WJ. Diffusion MRI in three types of anoxic encephalopathy. J Neurol Sci 2002; 196: 37^ 0. 6. Takahashi S, Higano S, Ishii K, et al. Hypoxic brain damage: cortical laminar necrosis and delayed changes in white matter at sequential MR imaging. Radiology 1993; 189: 449- 56. 295 J Neuro- Ophthalmol, Vol. 27, No. 4, 2007 Margolin et al 7. Roine RO, Raininko R, Erkinjuntti T. Magnetic resonance imaging findings associated with cardiac arrest. Stroke 1993; 24: 1005- 14. 8. Adams JH, Brierley JB, Connor RC. The effects of systemic hypotension upon the human brain: clinical and neuropathological observations in 11 cases. Brain 1966; 89: 235- 68. 9. Trobe JD. The Neurology of Vision. New York: Oxford University Press; 2001: 310. 10. Aldrich MS, Alessi AG, Beck RW, et al. Cortical blindness: etiology, diagnosis, and prognosis. Ann Neurol 1987; 21: 149- 58. 11. Back SA, Rivkees SA. Emerging concepts in periventricular white matter injury. Semin Perinatol 2004; 28: 405- 14. 12. Rivkin MJ, Volpe JJ. Hypoxic- ischemic brain injury in the newborn. Semin Neurol 1993; 13: 30- 9. 13. Volpe JJ. Neurobiology of periventricular leukomalacia in the premature infant. Pediatr Res 2001; 50: 553- 62. 14. Wood NS, Markow N, Costeloe K, et al. Neurologic and developmental disability after extremely preterm birth: EPICure Study Group. N Engl JMed 2000; 343: 378- 84. 15. Hoyt WF, Walsh FB. Cortical blindness with partial recovery following acute cerebral anoxia from cardiac arrest. AMA Arch Ophthalmol 1958; 60: 1061- 9. 16. Montero J, Pena J, Genis D, et al. Balint's syndrome: report of four cases with watershed parieto- occipital lesions from vertebrobasilar ischemia or systemic hypotension. Acta Neurol Belg 1982; 82: 270- 8. 17. Els T, Kassubek J, Kubalek R, et al. Diffusion- weighted MRI during early global cerebral hypoxia: a predictor for clinical outcome? Acta Neurol Scand 2004; 110: 361- 7. 18. McKinney AM, Teksam M, Felice R, et al. Diffusion- weighted imaging in the setting of diffuse cortical laminar necrosis and hypoxic- ischemic encephalopathy. AJNR Am JNeuroradiol 2004; 25: 1659- 65. 19. Sawada H, Udaka F, Seriu N, et al. MRI demonstration of cortical laminar necrosis and delayed white matter injury in anoxic encephalopathy. Neuroradiology 1990; 32: 319- 21. 20. Asao C, Korogi Y, Shimomura O, et al. MR findings of hypoxic damage of the bilateral striate cortices: a case report. Comput Med Imaging Graph 1998; 22: 417- 20. 21. Barkovich AJ, Ail FA, Rowley HA, et al. Imaging patterns of neonatal hypoglycemia. AJNR Am J Neuroradiol 1998; 19: 523- 8. 22. Asian Y, Dine H. MR findings of neonatal hypoglycemia. AJNR Am J Neuroradiol 1997; 18: 994- 6. 23. Spar JA, Lewine JD, Orrison WW, Jr. Neonatal hypoglycemia: CT and MR findings. AJNR Am J Neuroradiol 1994; 15: 1477- 8. 24. Kim SY, Goo HW, Lim KH, et al. Neonatal hypoglycaemic encephalopathy: diffusion- weighted imaging and proton MR spectroscopy. Pediatr Radiol 2006; 36: 144- 8. 25. Alkalay AL, Flores- Sarnat L, Sarnat HB, et al. Brain imaging findings in neonatal hypoglycemia: case report and review of 23 cases. Clin Pediatr 2005; 44: 783- 90. 26. Finelli PF Diffusion- weighted MR in hypoglycemic coma. Neurol-ogy 2001; 57: 933. 27. Fujioka M, Okuchi K, Hiramatsu KI, et al. Specific changes in human brain after hypoglycemic injury. Stroke 1997; 28: 584- 7. 28. Mori F, Nishie M, Houzen H, et al. Hypoglycemic encephalopathy with extensive lesions in the cerebral white matter. Neuropathology 2006; 26: 147- 52. 296 © 2007 Lippincott Williams & Wilkins [VBtraumaticvisualloss] [VBpostconcussionsyndrome] |
