Professional and Linguistic Assessments Board (PLAB) Practice Exam

What outcome is expected if there is occlusion of the anterior cerebral artery?

1. Contralateral facial droop

2. Contralateral lower limb weakness

3. Contralateral arm weakness

4. Contralateral speech difficulties

The correct answer is: Contralateral lower limb weakness

The occlusion of the anterior cerebral artery primarily affects the medial portions of the frontal lobes and the parietal lobes. This vascular territory is responsible for supplying blood to areas involved in motor and sensory functions of the lower limbs. When the anterior cerebral artery is occluded, the areas governing motor control of the lower limbs may suffer ischemic damage. Consequently, patients typically exhibit weakness (paresis) in the contralateral lower limb because the motor pathways responsible for voluntary movement are affected. The characteristic presentation often includes more pronounced weakness in the leg compared to the arm, reflecting the homunculus representation in the primary motor cortex where lower limb control is localized more medially. In contrast, damage to other arteries may lead to different presentations. For instance, occlusion of the middle cerebral artery is more likely to result in arm weakness and speech difficulties due to its role in supplying regions involved in upper limb control and language function. Therefore, the expected outcome from an anterior cerebral artery occlusion indeed centers on contralateral lower limb weakness.