Neureradielogl

Neuroradiol0gy 16, 299-301 (1978)

© by Springer-Ver!ag1978

CT in" H o m o n y m o u s H e m i a n o p i a S. Kan and T. Matsubayashi Department of Radiology,Kitasato University School of Medicine, Sagamihara-shi, Kanagawa-ken, Japan

Summary. Computed tomography (CT) is useful for demonstrating a lesion of the optic pathway, because a slice of the brain almost parallel to the optic pathway can be viewed and the relationship between the optic pathway and the extent of the lesion can be demonstrated. We studied 53 cases ofhomonymous hemianopia by CT. In 85% of our cases, positive CT findings were obtained. When the lesion was in the occipital lobe, correlation between the size of the lesion and the type of visual field defect was observed.

Table 1. Location of the lesions of homonymous hemianopia in 44 cases Optic tract Lateral geniculate body Optic radiation: anterior (optic peduncle) middle Meyer's loop other posterior

Materials and Methods CT scans were performed on 53 patients with homonymoushemianopia diagnosed by confrontation test or quantitative perimetry. CT was performed with ACTA 0100 at 20° to Reid's baseline. Contrast enhancement was achieved by intravenous infusion of 65% meglumine diatrizoate. It was found that 39 of the causative lesions were CVD (74%), 5 were brain tumors (9%), and 9 were others (17%).

Results Positive CT findings were obtained in 44 out of 53 cases, i.e., 85%. The locations in these 44 cases are listed in Table 1. Homonymous hemianopia caused by lesion of the optic tract was noted in the case with craniopharyngioma. There was no case with lesion of the lateral geniculate body. The optic radiation can be divided into three parts - anterior, middle, and posterior. The anterior part of

5 2 15 20

Striate area Not localized

Several types of defects in the visual field are caused by lesion of the optic pathway, and computed tomography (CT) is an effective method of determining the location of the lesion.

1 0

1

the optic radiation extends superiorly from the lateral geniculate body to the retrolenticularportion of the internal capsule, at which point visual radiation originates. The anterior part of the optic radiation is called the optic peduncle. Homonymous hemianopia caused by lesion o f the optic peduncle was found where thalamic hemorrhage or middle cerebral artery occlusion had taken place. The middle part of the optic radiation fans out, passing to the outer side of the temporal and posterior horns of the lateral ventricle. Homonymous hemianopia caused by lesion of Meyer's loop was seen in the case with temporal lobe tumor and in the postoperated case of temporal lobe. The visual field defect was upper quadrantanopia. Lesion of other middle parts of the optic radiation was caused by middle cerebral artery occlusion; in these cases a large low-density area of the MCA region was noted, which touched the outer side of the lateral ventricle. Due to other neurologic symptoms, quantitative perimetry could not be carried out. Consequently it was not ascertained whether the visual field defect had macular sparing. Lesion of the occipital lobe caused damage in the optic radiation and the striate area. Correlation between the extent of the lesion of the occipital lobe and the type of visual field defect was examined. An index of the extent of the lesion of the occipital lobe was postu-

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300 lated as described below. Occipital lobe lesions appeared in cases which were given quantitative perimetry and in cases of cortical blindness. The size of an occipital lobe is defined as 1.0. The extent of the lesion of an occipital • lobe was compared with the size of the occipital lobe. A slight enlargement of an occipital horn is def'med as 0.5. Then the size of the upper and lower slices of 4 cm thickness on the CT scan was measured and the index obtained. The mean value of the index of each type of visual field defect was calculated. The result is as follows: quadrantanopia had a mean value of 0.8, homonymous hemianopia with macular sparing 0.7, homonymous hemianopia without macular sparing 1.6, and cortical blindness 3.0. When the lesion was small, the visual field defect was quadrantanopia or homonymous hemianopia with macular sparing. But when the lesion was large, the visual field defect was complete homonymous hemianopia. In the case of homonymous hemianopia with macular sparing, the occipital pole was not involved on the CT image. When the lesion was found in bilateral occipital lobes, cortical blindness was evident. The extent of the lesion of the upper and lower slices of 4 cm thickness on the CT scan was compared in the cases of quadrantanopia. In 2 cases out of 4, CT findings were consistent with the type of visual field defect. In the case of upper quadrantanopia, there was a difference in the extent of the lesion of the occipital lobe in the upper and lower slices of 4 cm thickness on the CT scan. The lower slice showed a greater extent of lesion. This finding correlated well with the fact that the lower lip of the calcarine fissure represents the upper visual field. CT and quantitative perimetry were repeatedly carried out in three cases with homonymous hemianopia. In two cases the visual field defect improved and at the same time the lesion on the CT image disappeared. Out of 9 cases of homonymous hemianopia with normal CT findings, 8 cases received quantitative perimetry. These included homonymous hemianopia with macular sparing, homonymous hemianopia without macular sparing, and quadrantanopia, but no case of cortical blindness had a normal CT scan.

Discussion Correlation between the visual field defect caused by occipital lesions and neuroradiologic study was done by Hoyt and Newton [1]. Magnification cerebral angiography with subtraction technique was used and sites of occlusion of arteries and areas of cortical avascularity were discovered. Some difficulties are, however, still present. One is superimposition of the right and left po sterior cerebral arteries and their branches in the lateral projection, and the variability in the course of cortical arteries in the parieto-occipital and calcarine fissures. It is also difficult to know by angiography alone the actual extent of the lesion caused by hematoma or other avascular mass lesion.

S. Kan and T. Matsubayashi: CT in Homonymous Hemianopia Correlation between the visual field defect and CT was done by McAuley and Russel [2], and Orr et al. [3]. McAuley and Russel's cases were vascular diseases of the visual radiation and cortex; Orr et al.'s cases were occipital lobe lesion. CT scan both shows the relationship between the lesion and optic pathway, and also provides etiologic information. In 85% of our cases, positive CT findings were obtained. Therefore the location of the lesion of the optic pathway was approximately determined by CT. Another advantage of CT is noninvasiveness, so that CT scan can be done repeatedly. In following up the patients with homonymous hemianopia, CT scan can be done simultaneously with visual field examination. When the lesion is in the occipital lobe, correlation between the extent of the lesion and the type of visual field defect can be observed. When the lesion is large, the visual field defect is homonymous hemianopia without macular sparing. When the lesion is small, the visual field defect is quadrantanopia or homonymous~hemianopia with macular sparing. This observation was also made by McAuley and Russel. There has been much discussion concerning macular sparing. In our two cases of homonymous hemianopia with macular sparing the occipital pole was spared on the CT image. Orr et al. stated that in their cases of macular sparing, the calcarine cortex was found destroyed in its more anterior portions, but the occipital tip was spared. But McAuley and Russel reported that, although some of their patients with macular sparing had a CT scan indicating the survival of the posterior pole, this was not a regular finding. This may be due to the possibility that the posterior portion of the CT image at the occipital lobe level does not always show a macular region. There are two reports on comprehensive series of homonymous hemianopia. Smith reported a series of 100 homonymous hemianopias [4]. The causative lesions were CVD (42%), tumors (38%), and others (20%). Trobe et al. reported 104 isolated homonymous hemianopias [5]. Their results were quite different: 89% had vascular lesions, 8% had other lesions, and 3% had tumors. The discrepancies may be due to different criteria for patient selection. Smith's cases were all patients with homonymous hemianopia, not necessarily isolated. Trobe's cases were all isolated homonymous hemianopia (without other neurologic signs), Our cases were similar to those of Trobe et al. Our cases were patients with homonymous hemianopia who had CT scans. To correlate CT and visual field defect, not only the extent of the lesion in the axial plane, but the vertical extension Of the lesion is also important. Therefore, as well as axial CT, coronal and sagittal CT are also necessary. If the calcarine fissures were visualized on coronal or sagittal planes, then a closer correlation between CT and the visual field defect might be obtained.

S. Kan and T. Matsubayashi: CT in Homonymous Hemianopia

References 1. Hoyt, W.F., Newton, T.H.: Angiographic changes with occlusion of arteries that supply the visual cortex. N.Z. Med. J. 72, 310-317 (1970) 2. McAuley, D.L.F., Russel, R.W.R.: Vascular diseases of the visual radiation and cortex. In: Computerized axial tomography in clinical practice, pp, 251-367 (eds. G.H. du Boulay, I.F. Moseley). Berlin-Heidelberg-New York: Springer 1977 3. Orr, L.S., Schats, N.J., Gonzalez, C.F., Savino, P.J., Corbett, J.J.: Computerized axial tomography in evaluation of occipital lobe lesion. In: Neuro-ophthalmology update, pp. 251367 (ed. J.L. Smith). New York: Masson 1977

301 4. Smith, J i . : Homonymous hemianopia: A review of one hundred cases. Am. J. Ophthalmol. 54,616-622 (1962) 5. Trobe, J.D., Lorber, M.L., Sehlezinger, N.S.: Isolated homonymons hemianopia. Arch. Ophthalmol. 89, 377-38i (1973)

S. Karl, MD Department of Radiology Kitasato University School of Medicine 1 Asamizodal Sagamihara-shi Kanagawa-ken 228, Japan

CT in homonymous hemianopia.

Neureradielogl Neuroradiol0gy 16, 299-301 (1978) © by Springer-Ver!ag1978 CT in" H o m o n y m o u s H e m i a n o p i a S. Kan and T. Matsubayashi...
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