Rosh Emergency Medicine Practice Test

A patient presents with right-sided weakness. Which vessel is most likely responsible for this clinical manifestation?

1. A. Anterior cerebral artery

2. B. Middle cerebral artery

3. C. Posterior cerebral artery

4. D. Vertebral artery

The correct answer is: B. Middle cerebral artery

The presence of right-sided weakness in a patient typically indicates a neurological issue that is affecting the part of the brain responsible for motor control on the opposite side of the body—this is due to the crossing of motor pathways in the brain. The middle cerebral artery (MCA) is the vessel most commonly associated with motor deficits, especially for upper limb and facial control. The MCA supplies a significant portion of the lateral aspects of the cerebral hemispheres, which includes areas that control motor function for much of the upper body, face, and speech. In cases where there is an infarction or occlusion in the MCA territory, it often results in pronounced weakness on the opposite side of the body—in this case, the right side. Therefore, when evaluating a patient with right-sided weakness, the involvement of the middle cerebral artery is the most likely cause. Other vessels may contribute to weakness, but they would produce different patterns of deficits or involve other regions of the body. The anterior cerebral artery primarily supplies the medial surfaces of the frontal lobes and is more associated with lower limb weakness, whereas the posterior cerebral artery primarily affects vision and is not typically linked to motor weakness. The vertebral artery supplies the brainstem and posterior fossa structures, and while issues here