What is the sylvian triangle?

• A. Proximal portion of the anterior cerebral branch to the loops of the middle cerebral branch and the middle cerebral itself
• B. Junction of internal and external carotid arteries
• C. Optic chiasm region
• D. Basilar tip

Answer: (A)

The Sylvian triangle is a vascular landmark inside the Sylvian fissure that marks the area where the anterior cerebral artery (ACA) contributes branches toward the middle cerebral artery (MCA) loops and the MCA trunk itself. In other words, it’s the proximal portion of the ACA that lies in relation to the MCA’s loops, creating a triangular region within the fissure. This concept is useful during cerebral angiography and neurosurgical approaches to the MCA territory because it helps localize the first segments of the MCA and the adjacent ACA branches as they course in the Sylvian fissure.

The other options describe different brain landmarks that are not the Sylvian triangle: the junction of the internal and external carotid arteries is the carotid bifurcation; the optic chiasm region is where the optic nerves cross; and the basilar tip is a posterior circulation landmark at the top of the brainstem.