A 65-year-old male with a past medical history of poorly controlled hypertension presents with new onset unilateral arm and leg weakness. What is the most likely location of the vascular obstruction?

In this scenario, the patient's presentation of new onset unilateral arm and leg weakness suggests a stroke, and the location of the vascular obstruction is key in determining the affected areas of the brain and the specific deficits observed. The most likely cause of unilateral weakness in an individual with poorly controlled hypertension points towards a lacunar stroke, which typically occurs in deep structures of the brain, resulting from small vessel disease.

Lacunar strokes commonly affect areas that control motor function, often involving regions such as the internal capsule or the thalamus. These strokes can lead to distinctive patterns of weakness, such as pure motor weakness, which aligns with the unilateral arm and leg weakness observed in this patient.

In contrast, the anterior cerebral artery typically supplies the medial parts of the frontal lobes and the superior medial parietal lobes, affecting the opposite leg more than the arm. The middle cerebral artery supplies a larger region that includes the lateral aspects of the frontal, parietal, and temporal lobes, and would generally lead to more varied deficits, including more marked arm weakness than leg weakness. The posterior cerebral artery primarily supplies the occipital lobe and parts of the temporal lobe, and would not typically present with weakness of the arms and legs.