A 57-year-old man is brought to the emergency department following a generalized tonic-clonic seizure. His wife reports that he has no history of seizures. However, she says that he has been complaining of intermittent headaches, memory loss, and problems with his vision for the past 2 weeks. Brain imaging shows a solitary mass within the right temporal lobe. Which of the following visual field defects is most likely present in this patient?

Question

Quizplus · Accepted Answer

11ec160b_35d6_e63b_9249_7345e994e3d2_MD0001_00 Damage to the visual pathway produces distinct types of visual field defects depending on the location of the lesion. Visual perception begins with light from the nasal visual fields striking the temporal side of each retina and light from the temporal visual fields striking the nasal side of each retina. Information from the retina is then transmitted by the optic nerves to the optic chiasm. At the optic chiasm, optic nerve fibers from the nasal half of each retina cross and project into the contralateral optic tract. In contrast, nerve fibers from the temporal parts pass into the ipsilateral optic tract. The optic tract thus contains nerve fibers from the temporal part of the ipsilateral retina and the nasal part of the contralateral retina. Optic tract fibers project mainly to the lateral geniculate nucleus (LGN), but also project to superior colliculus (reflex gaze), pretectal area (light reflex), and the suprachiasmatic nucleus (circadian rhythms). Axons from the LGN that project to the striate (primary visual) cortex are known as the optic radiation (or geniculocalcarine tract). The lower fibers of the optic radiation carry information from the lower retina (upper contralateral visual field) and take a circuitous route anteriorly into the temporal lobe (Meyer's loop) before reaching the lingual gyrus of the striate cortex. The upper fibers of the optic radiation carry information from the upper retina (lower contralateral visual field) and pass more directly from the LGN through the parietal lobe to reach the cuneus gyrus of the striate cortex. Lesions in the temporal lobe can disrupt Meyer's loop and produce a contralateral superior quadrantanopia. Temporal lobe lesions can also produce other neurologic manifestations, including aphasia (dominant hemisphere lesions), memory deficits, seizures (complex partial and tonic-clonic), and hallucinations (auditory, olfactory, and visual). Educational objective: Injury to Meyer's loop in the temporal lobe results in contralateral superior quadrantanopia.

A 57-Year-Old Man Is Brought to the Emergency Department Following