Walsh & Hoyt: Topical Diagnosis of Lesions of the Optic Radiation

Efferent projection fibers from and afferent projection fibers to the cerebral cortex traverse the subcortical white matter, where they form a radiating mass of fibers, the corona radiata, which converges toward the brain stem. In the rostral brain stem, the fibers form a broad but compact fiber band, the internal capsule, that is bordered medially by the thalamus and caudate nucleus and laterally by the lenticular nucleus. The afferent fibers make up the thalamocortical radiation in the internal capsule. The efferent fiber bundles include (a) the corticospinal and corticobulbar tracts; (b) the frontopontine tract from the prefrontal and precentral regions of the cerebral cortex; (c) the temporoparietopontine tract from the temporal and parietal lobes; and (d) the optic radiation, which begins in the lateral geniculate body and occupies only a small region of the capsule, since it does not proceed to the brain stem. The internal capsule is thus composed of all fibers, afferent and efferent, that go to, or come from, the cerebral cortex. Lesions of the internal capsule. Lesions of the temporal lobe. Lesions of the parietal lobe.