**Question:** For sudden, unilateral or bilateral weakness, sensory loss, disorder of ocular motility, loss of facial sensation, ataxia in cerebrovascular disease, select the site of the lesion.

**Core Concept:** Cerebrovascular disease refers to conditions affecting the blood vessels supplying the brain. These conditions can lead to a range of neurological symptoms due to impaired blood flow or occlusion of blood vessels.

**Why the Correct Answer is Right:** The correct answer, **C.** Basilar artery, is chosen because it is a major cerebrovascular structure that supplies blood to the lower brainstem and spinal cord. When the basilar artery is occluded or compromised, it can lead to the described symptoms of cerebrovascular disease.

Basilar artery is a long, slender, and fusiform artery that arises from the vertebral arteries (two arteries in the neck that supply blood to the head and neck). The basilar artery supplies blood to the pons (a part of the brainstem) and the medulla oblongata. The pons is involved in controlling ocular motility, facial sensation, and coordination of breathing and swallowing. The medulla oblongata is responsible for controlling respiratory rate, heart rate, and blood pressure, as well as regulating swallowing, coughing, and gag reflexes.

**Why Each Wrong Option is Incorrect:**

A. **Superior cerebellar artery (SCA) and middle cerebellar artery (MCA)** are incorrect because they supply blood to different regions of the brain. The SCA provides blood to the cerebellar vermis, which is responsible for coordination and balance, while the MCA supplies blood to the frontal and parietal lobes, which play a role in higher cognitive functions. Neither of these arteries is primarily responsible for the described symptoms.

B. **Anterior cerebral artery (ACA)** is incorrect because it supplies blood to the frontal lobes of the brain, which are involved in higher cognitive functions, language, and emotions. These lobes are not primarily responsible for the described symptoms.

D. **Internal carotid artery (ICA)** is incorrect because it supplies blood to the cerebral hemispheres, which are responsible for higher cognitive functions, language, and emotions. These regions are not primarily affected in the described symptoms.

**Clinical Pearl:** Understanding the arterial supply to different regions of the brain is crucial when diagnosing neurological symptoms. The symptoms described are predominantly caused by lesions affecting the brainstem, cerebellum, and spinal cord, all of which are supplied by the basilar artery (BA). The BA is formed by the union of the P1 segment of the vertebral artery and the posterior cerebral artery (PCA). It supplies blood to the pons, medulla oblongata, and cerebellum, which are responsible for the described symptoms.

**Correct Answer:** **Basilar artery (BA)** is the correct answer because it supplies blood to the brainstem, cerebellum, and spinal cord, which are involved in the described symptoms. The BA is formed by the union of the P1 segment of the vertebral artery and the posterior cerebral artery (PCA). The BA supplies blood to the pons, medulla oblongata