Clinical and Diffusion Tensor MRI Findings in Congenital Homonymous Hemianopia

A 29-year-old woman underwent brain MRI for increasing frequency of migraine headaches. The MRI report recommended further evaluation for septo-optic dysplasia. The patient reported no visual deficits. Her examination showed normal visual acuities, color vision, pupillary function, and a normal optic disc in the right eye with mild temporal disc pallor in the left eye. Automated perimetry revealed an incongruous left homonymous hemianopia (Fig. 1). Optical coherence tomography (OCT) showed thinning of the retinal nerve fiber layer to 60 µm in the right eye and 54 µm in the left eye. There was ganglion cell layer thinning in a hemianopic pattern with temporal thinning in the right eye and nasal thinning in the left eye. This corresponded with the left homonymous hemianopia.

Photo Essay Section Editors: Melissa W. Ko, MD Dean M. Cestari, MD Clinical and Diffusion Tensor MRI Findings in Congenital Homonymous Hemianopia Joanne Rispoli, MD, Meagan Seay, DO, Melissa Sum, MD, Janet C. Rucker, MD, Timothy M. Shepherd, MD, PhD FIG. 1. Automated visual field testing reveals an incongruous left homonymous hemianopia. A 29-year-old woman underwent brain MRI for increasing frequency of migraine headaches. The MRI report recommended further evaluation for septo-optic dysplasia. The patient reported no visual deficits. Her examination showed normal visual acuities, color vision, pupillary function, and a normal optic disc in the right eye with mild temporal disc pallor in the left eye. Automated perimetry revealed an incongruous left homonymous hemianopia (Fig. 1). Optical coherence tomography (OCT) showed thinning of the retinal nerve fiber layer to 60 mm in the right eye and Departments of Radiology (JR, TMS); Neurology (MS, JR); Endocrinology (MS); and Ophthalmology (JR), New York University Langone Medical Center, New York, New York. T. M. Shepherd (co-founder Velona Technologies, a start-up for medical devices used in image-guided interventions). The remaining authors have no conflicts of interests to disclose. Address correspondence to Timothy M. Shepherd, MD, PhD, Department of Radiology, NYU Langone Medical Center, 660 First Ave., New York, NY 10016; E-mail: [e-mail] Rispoli et al: J Neuro-Ophthalmol 2019; 39: 401-404 54 mm in the left eye. There was ganglion cell layer thinning in a hemianopic pattern with temporal thinning in the right eye and nasal thinning in the left eye. This corresponded with the left homonymous hemianopia (Fig. 2). Endocrine studies included a normal pituitary hormone panel with the exception of a TSH of 0.36 mIU/mL (normal:0.49-4.70 mIU/mL). Free T4 level was 1.1 ng/dL (normal: 0.9-2.2 ng/dL). Clinically, the patient was euthyroid. A dedicated 3-T MRI of the orbits demonstrated absent septum pellucidum, thinning of both optic nerves, and asymmetric thinning of the right optic tract (Figs. 3, 4). The pituitary gland measured 4 mm in craniocaudal height, which was relatively small for the patient's age and sex (1). There also was a closed-lip schizencephaly of the right lateral ventricle atrium with associated overlying polymicrogyria (Fig. 4). Further evaluation with high-resolution reduced field of view diffusion tensor imaging more precisely delineated asymmetry of the right optic radiation superior to the temporal horn (Fig. 4B) and more posteriorly along the 401 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Photo Essay FIG. 2. Optical coherence tomography of the macular ganglion cell layer shows a hemianopic pattern of thinning with temporal thinning in the right eye and nasal thinning in the left eye. OD, right eye; OS, left eye. inferolateral wall of the lateral ventricle atrium (Fig. 4C). Diffusion tractography was not used because it is highly variable and lacks reproducibility across individuals particularly for the visual pathways. Clinical and radiographic findings were consistent with the diagnosis of congenital homonymous hemianopia involving the right optic tract and radiation. Initially, we suspected a right optic tract lesion based on the findings of a left incongruous homonymous hemianopia, OCT abnormalities, and optic nerve pallor. However, in addition to optic tract thinning, MRI demonstrated schizencephaly, polymicrogyria, and thinning of the right optic radiation. Optic tract lesions are commonly, although not always, associated with an afferent pupillary defect (APD). Lesions of the optic tract without an APD have been reported with incongruous homonymous hemianopia, where there is less dense involvement of the temporal hemifield in the eye contralateral to the tract lesion (2), as seen in our patient. The visual field defect also potentially could localize to the right superior optic FIG. 3. MRI and diffusion tensor imaging. Coregistered axial T1 image (left) and direction-encoded diffusion tensor image (right; red = left-right; blue = craniocaudal; green = anterior-posterior fiber orientation) demonstrate asymmetry in the optic tracts along the anterolateral margins of the rostral cerebral peduncles. Compared with the left optic tract (arrowhead), the right optic tract (arrows) is thin and less bright on the T1 scan. There is absence of green anterior-posterior tubular structure in the expected location of the right optic tract on the direction-encoded diffusion tensor images (arrows) compared with the left optic tract (arrowheads). 402 Rispoli et al: J Neuro-Ophthalmol 2019; 39: 401-404 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Photo Essay FIG. 4. MRI and diffusion tensor imaging. A. Coronal T2 imaging through the optic chiasm demonstrates marked thinning of the right lateral aspect of the optic chiasm (arrow). There also is absence of the septum pellucidum. Corresponding diffusion tensor imaging confirms right chiasmal asymmetry (arrow) as compared to the more normal appearance of the left lateral aspect of the optic chiasm (green fibers, arrowhead). B. Coronal T2 MRI shows a closed-lip schizencephaly with associated polymicrogyria (arrows). Corresponding diffusion tensor imaging demonstrates an asymmetry in the size of the proximal right optic radiation (arrow) compared with the normal contralateral left optic radiations (green fibers, arrowhead). Note the fimbria/fornix is a much smaller structure with a similar orientation located inferior to this position that is not detectable with diffusion tensor imaging in vivo due to partial volume effects. C. Coronal T2 scan reveals closed-lip schizencephaly extending to the region of the optic radiations (arrows). On diffusion tensor imaging, there is loss of the right optic radiation (arrows) compared with the normal left optic radiation (green fibers, arrowheads). radiation; this may explain may explain the denser visual field deficit in the inferior left quadrant. Such retrogeniculate lesions also typically do not cause an APD. The few reported patients with congenital homonymous hemianopia typically are asymptomatic at the time of diagnosis (3). Early injury to the retrochiasmatic visual pathway may occur in utero, perinatally, or early in life (4). OCT, particularly of the ganglion cell layer, is useful to assess retrograde transynaptic degeneration in congenital homonymous hemianopia due to retrogeniculate hemianopia, as well as in primary optic tract hypoplasia (5). Previously cited causes of congenital homonymous hemianopia, as well as classic septo-optic dysplasia with acuity and color vision loss, have included porencephalic cysts and brain malformations (6-8). The periventricular Rispoli et al: J Neuro-Ophthalmol 2019; 39: 401-404 location of the optic radiations also makes the visual pathway susceptible to periventricular leukomalacia as a result of in utero ischemia (4). Our patient's clinical examination suggested an optic tract lesion; however, the region of polymicogyria and schizencephaly in the expected location of the superior right optic radiations could potentially represent the underlying etiology for this patient's congenital homonymous hemianopia (Fig. 4C) and may have secondarily led to optic tract retrograde degeneration and/or maldevelopment. The other possibilities are that the optic tract hypoplasia induced the retrogeniculate injury and cortical malformations, or that true primary visual pathway hypoplasia with coexistent but noncausative cortical malformations were induced by the same in utero or perinatal insult (7,8). 403 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Photo Essay Our case highlights the utility of diffusion tensor imaging in evaluation of the visual pathways. Colorencoded fractional anisotropy maps better demonstrate asymmetry and anatomy of the retrochiasmatic optic pathway compared with conventional MRI (9). The clear left-right asymmetry in the direction-encoded fractional anisotropy maps detected in our patient not only allowed for localization of the anatomical abnormality but also the extent of visual pathway involvement. STATEMENT OF AUTHORSHIP Category 1: a. conception and design: J. Rispoli, M. Seay, M. Sum, J. Rucker, and T. M. Shepherd; b. acquisition of data: J. Rispoli, M. Seay, M. Sum, J. Rucker, and T. M. Shepherd; c. analysis and interpretation of data: J. Rispoli, M. Seay, M. Sum, J. Rucker, and T. M. Shepherd. Category 2: a. drafting the manuscript: J. Rispoli, M. Seay, M. Sum, J. Rucker, and T. M. Shepherd; b. revising it for intellectual content: J. Rispoli, M. Seay, M. Sum, J. Rucker, and T. M. Shepherd. Category 3: a. final approval of the completed manuscript: J. Rispoli, M. Seay, M. Sum, J. Rucker, and T. M. 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