Anatomy and Course of the Basilar Artery
This unpaired vessel forms at the junction of the medulla oblongata and the pons by the confluence of the right and left vertebral arteries (aa. vertebrales). The a. basilaris then ascends rostrally along the anterior (ventral) surface of the brainstem, lying in the vertical basilar sulcus (sulcus basilaris pontis) of the pons. The sulcus itself is anatomically formed not by the pressure of the vessel, but by the prominent pyramidal tracts bulging on either side.
Branches of the Basilar Artery
As it ascends, the main trunk gives off numerous branches:
- Pontine arteries (aa. pontis) — multiple penetrating vessels divided into paramedian, short circumferential, and long circumferential branches that supply the pons.
- Anterior inferior cerebellar artery (a. cerebelli inferior anterior / AICA) — arises from the lower third of the basilar artery and supplies the anteroinferior surface of the cerebellum.
- Labyrinthine artery (a. labyrinthi) — a slender branch traveling to the inner ear through the internal acoustic meatus alongside the vestibulocochlear nerve; it frequently arises from the anterior inferior cerebellar artery.
- Superior cerebellar artery (a. cerebelli superior) — branches off the basilar artery just proximal to its bifurcation, courses around the cerebral peduncle, and supplies the superior surface of the cerebellum, the superior vermis, and the choroid plexus of the third ventricle.
- Posterior cerebral arteries (aa. cerebri posteriores) — the terminal branches of the basilar artery.
Territory and Function
Blood supply to the structures of the posterior cranial fossa is derived from the vertebrobasilar system. The a. basilaris supplies the ventral pons and ventral midbrain, as well as sending branches to the cerebellum. Occlusion of its penetrating branches leads to brainstem ischemia syndromes, including alternating brainstem syndromes.
Clinical Significance
Atherosclerotic stenoses and occlusions commonly affect the basilar artery. Saccular and fusiform aneurysms can develop on the basilar trunk and at its bifurcation. Basilar artery aneurysms account for approximately 10% of intracranial aneurysms, with 7% located at the bifurcation and 3% along the trunk. Large aneurysms of this vessel can cause brainstem compression.