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 vision disturbances for the past 2 weeks. Brain imaging shows a solitary mass within the right temporal lobe. Which of the following visual field defects (areas of vision loss in black) is most likely present in this patient?
Show Explanatory Sources
After traversing the lateral geniculate nucleus, visual information travels to the primary visual cortex in the occipital lobe by way of the optic radiations. The optic radiations fan out as they project posteriorly into 2 major pathways:
Superior optic radiations carry information from the superior retina/inferior visual field. They travel through the parietal lobe, so lesions in that area result in contralateral inferior quadrant visual field defects (ie, contralateral homonymous inferior quadrantanopia) (Choice E).
Inferior optic radiations carry information from the inferior retina/superior visual field. They travel through the temporal lobe (Meyer loop), so lesions in that area (such as this patient's temporal lobe mass) result in contralateral superior quadrant visual field defects (ie, contralateral homonymous superior quadrantanopia).
Therefore, this patient's tumor in the right temporal lobe is likely impacting the inferior optic radiations, causing a left homonymous (both eyes the same) superior quadrantanopia.
(Choice A) Monocular vision loss results from a lesion anterior to the optic chiasm, including lesions to the optic nerve, retina, or globe.
(Choice B) In the optic chiasm, fibers from the nasal retina (which process the temporal visual field) cross so that the hemivisual fields from both eyes are processed in the same contralateral hemisphere. A lesion that affects these crossing fibers in the middle of the optic chiasm can produce bitemporal hemianopia.
(Choice C) Left homonymous hemianopia may occur with lesions to the right optic tract or the right occipital cortex. It may also occur with lesions to the optic radiations, but only if they affect both the superior and inferior optic radiations. This is less likely to occur with a mass lesion localized within the temporal lobe.
Educational objective:
The inferior optic radiations travel through the temporal lobe in the Meyer loop. They carry information from the inferior retina, which covers the superior visual field. Therefore, temporal lobe lesions can result in contralateral homonymous superior quadrantanopia.