Right Parietal Cortex Lesion
This patient has a lesion affecting the right parietal cortex, specifically the right inferior parietal lobule. The combination of left inferior quadrantanopia with hemispatial neglect (evidenced by placing all clock numbers on the right side and lack of awareness of visual deficits) localizes to the right posterior parietal region 1, 2.
Clinical Reasoning
Visual Field Defect Localization
Left inferior quadrantanopia in both eyes indicates a post-chiasmal lesion affecting the contralateral (right) hemisphere, as homonymous visual field defects require damage beyond the optic chiasm 3.
Inferior quadrantanopias are most commonly caused by parietal lobe lesions (22% of cases) when neurologically isolated, though occipital lesions account for the majority (76%) 2.
The key distinguishing feature is that parietal lobe quadrantanopias are typically associated with other localizing neurological signs (89% of cases), whereas occipital lobe lesions causing isolated quadrantanopias rarely have additional findings (6%) 2.
Hemispatial Neglect as the Localizing Sign
Hemispatial neglect—the failure to orient to, respond to, or report sensory events in contralateral space—is the critical additional finding that definitively localizes this lesion to the right parietal cortex 1.
The clock drawing test demonstrates classic left-sided neglect, where the patient places all numbers on the right side, indicating impaired spatial awareness of the left hemispace 4.
Anosognosia (denial of visual problems) is characteristic of right parietal lesions causing neglect, as patients typically lack awareness of their deficit 1.
Damage to the right inferior parietal lobule of the posterior parietal cortex is specifically associated with egocentric, perceptual, and exploratory components of neglect affecting contralateral extrapersonal space 1.
Why Not Other Locations?
Right occipital lesions would cause the visual field defect but would not produce hemispatial neglect or the characteristic clock drawing abnormality 2.
Right temporal lesions can cause superior quadrantanopias (not inferior) and do not typically produce hemispatial neglect 2.
Left hemisphere lesions (occipital, parietal, or temporal) would cause right-sided visual field defects, not left-sided deficits 3.
White Matter Tract Involvement
The superior longitudinal fasciculus connecting parietal to frontal regions is frequently damaged in neglect patients, contributing to the attention and spatial awareness deficits 5.
Disrupted inter-hemispheric functional connectivity in the dorsal attention network, particularly involving the right superior parietal lobule, correlates with severity of neglect symptoms 6.