American Board of Psychiatry and Neurology (ABPN) Practice Exam

A 75-year-old woman shows signs of right foot paralysis with slight arm involvement. Which vascular territory is likely affected?

1. A. Right anterior choroidal artery

2. B. Left anterior cerebral artery

3. C. Small subcortical vessels

4. D. Deep penetrating vessels

The correct answer is: B. Left anterior cerebral artery

The scenario describes a right foot paralysis with slight arm involvement, which suggests a specific pattern of weakness that points towards a vascular territory likely affected by a stroke or another ischemic event. The anterior cerebral artery (ACA) supplies the medial portion of the frontal lobes as well as the superior medial parietal lobes. When there is occlusion or dysfunction of the left anterior cerebral artery, it primarily affects the motor areas responsible for controlling the lower extremities, particularly the foot. This results in a right foot paralysis due to the crossing fibers of the motor pathway at the level of the medulla. The slight arm involvement indicates additional effects, possibly affecting the proximal arm but primarily demonstrating weakness in the foot. The other vascular territories listed would not typically cause this specific pattern of motor impairment. For instance, the right anterior choroidal artery primarily supplies structures involved with the visual system and deep brain areas rather than peripheral motor function. Small subcortical vessels could contribute to various motor deficits but often do not produce such a localized deficit presenting predominantly as foot paralysis with minimal arm involvement. Lastly, the deep penetrating vessels primarily affect deeper structures including the basal ganglia and thalamus, which would lead to different presentations of motor deficits. Thus,