The basilar artery is formed by the fusion of which vessels and provides input to which parts of the brain?

• A. Anterior cerebral arteries supply spinal cord.
• B. Posterior cerebral arteries supply frontal lobe.
• C. Internal carotid arteries supply brainstem.
• D. Basilar artery is formed by fusion of vertebral arteries and supplies the brainstem and cerebellum.

Answer: (D)

Focus on how the posterior circulation is formed and what it feeds. The basilar artery is created by the fusion of the two vertebral arteries as they ascend into the skull. This single basilar trunk then supplies the brainstem and cerebellum with its branches and eventually gives rise to the posterior cerebral arteries, which feed the posterior aspects of the cerebral hemispheres.

That’s why the statement about the basilar artery being formed by the fusion of vertebral arteries and supplying the brainstem and cerebellum is correct. In contrast, the anterior cerebral arteries primarily supply medial frontal lobes and the superior medial parietal lobes, not the brainstem. The posterior cerebral arteries originate from the basilar system and supply the occipital and inferior temporal lobes, not the frontal region. The internal carotid arteries mainly contribute to the anterior and middle cerebral circulations and are not the origin of the brainstem’s supply.