Visual Field Deficit Following Right Temporal Lobe Tumor Resection
A patient who has undergone successful resection of a right temporal lobe tumor is most likely to develop a left superior quadrantanopsia due to disruption of Meyer's loop, the anterior portion of the optic radiation that courses through the temporal lobe.
Anatomical Basis
The optic radiations carry visual information from the lateral geniculate nucleus to the primary visual cortex. The inferior fibers of the optic radiation, known as Meyer's loop, course anteriorly through the temporal lobe before sweeping posteriorly toward the occipital cortex 1. These fibers carry information from the superior visual field of the contralateral eye.
- Right temporal lobe lesions disrupt Meyer's loop on that side, affecting fibers carrying information from the left superior visual field of both eyes 1
- This produces a left superior quadrantanopsia (loss of the left upper quadrant of vision in both eyes) 2
- The deficit is contralateral to the side of surgery and affects the superior quadrant specifically because Meyer's loop carries inferior retinal fibers (which represent superior visual field) 1
Clinical Evidence from Temporal Lobe Surgery
Superior quadrantanopsia is a well-recognized complication of anterior temporal lobe resection occurring specifically due to Meyer's loop disruption 2. In a large surgical series of 235 patients with temporal mediobasal tumors:
- Visual field deficits were present preoperatively in 12% of patients 3
- Significant new hemianopic defects (including quadrantanopias) occurred in 5.4% of patients postoperatively 3
- The authors noted that certain neurological disturbances, particularly quadrantanopia, seem to be unavoidable in temporal lobe surgery due to the complex anatomic structures 3
Why Not Other Options?
Left inferior quadrantanopsia would indicate a parietal lobe lesion affecting the superior optic radiations, not a temporal lobe lesion 1. Research demonstrates that:
- Inferior quadrantanopias are caused by occipital lobe lesions (76%), parietal lobe lesions (22%), or rarely temporal lobe lesions (2%) 1
- Superior quadrantanopias are caused by occipital lobe lesions (83%), temporal lobe lesions (13%), or rarely parietal lobe lesions (3%) 1
Right-sided deficits (right homonymous hemianopsia or right quadrantanopias) would indicate a left hemisphere lesion, not a right temporal lobe resection 4.
Left homonymous hemianopsia would require more extensive damage affecting the entire optic radiation or occipital cortex, not just the anterior temporal component 4.
Clinical Considerations
The EANO guidelines acknowledge that anticipated minor deficits such as quadrantanopia might be deemed acceptable during glioma surgery, but only after thorough shared decision-making with patients 4. This reflects the reality that:
- Preventing permanent neurological deficits is more important than extent of resection 4
- However, quadrantanopia is sometimes unavoidable when resecting temporal lobe lesions 3
- Patients should be informed preoperatively about this specific risk 4
Modern imaging techniques, including diffusion tensor imaging tractography, can visualize the optic radiation preoperatively and predict which patients are at highest risk for developing visual field defects following temporal lobe resection 2.