Optic Tract Lateral Geniculate Body

Complete lesions of both these structures cause dense contralateral homonymous hemianopias. Isolated syndromes involving these structures are rare. Incongruous homonymous hemianopias characterize partial optic tract and lateral geniculate body lesions (Fig. 8-7 (Figure Not Available) ). A contralateral relative afferent pupillary defect can accompany an optic tract lesion; much rarer pupillary abnormalities include contralateral mydriasis (Behr's pupil), and a hemianopic pupillary reactivity (Wernicke's pupil). Because of presynaptic interruption, patients may have bilateral optic atrophy with ipsilateral temporal pallor and contralateral "bowtie" or "band" atrophy. Visual acuity is normal in isolated tract lesions. Sellar and parasellar masses, especially craniopharyngiomas and aneurysms, commonly compress the optic tract.[4oi Isolated tract syndromes may also result from demyelination or rarely ischemia. Although it is often difficult to distinguish clinically between

Figure 8-7 (Figure Not Available) Visual pathways: correlation of lesion site and field defect, view of underside of the brain. Homonymous refers to a defect present in both eyes with the same laterality, whereas hemianopia refers to visual loss respecting the vertical meridian. Congruous fields are symmetrical in both eyes. Note that lesions of upper or lower occipital banks produce quadrantic defects, whereas lesions within temporal and parietal lobes cause field defects, which tend not to respect the horizontal meridian. (From Liu GT: Disorders of the eyes and eyelids. In Samuels MA, Feske S [eds]: The Office Practice of Neurology. New York, Churchill-Livingstone, 1996, p 43. Adapted from Mason C, Kandel ER:ln Kandel ER, Schwartz JH, Jessell T [eds]: Principles of Neural Science, 3rd ed. East Norwalk, CT, Appleton and Lange, 1991, p 437.)

lateral geniculate and tract syndromes, there are two unique exceptions owing to the geniculate's dual vascular supply. A congruous homonymous horizontal wedge-shaped sectoranopia results from lateral choroidal artery infarction, whereas upper and lower homonymous sectoranopias result from anterior choroidal artery occlusion.

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