Brainstem Arteries

 
Diagrams

The vertebral arteries help to supply the spinal cord  

The posterior spinal arteries and the two anterior spinal arteries, which fuse to form a single midline vessel, supply the upper cervical cord. For lower parts of the cord, the spinal arteries are reinforced by radicular arteries that are branches of the thoracic and abdominal aorta. There is a great deal of variability in this pattern. The artery of Adamkiewicz is one of the most important radicular arteries, and in some individuals it may provide the entire arterial supply for the lower two-thirds of the spinal cord.

The vertebral and basilar arteries supply the brainstem and cerebellum.  
Perhaps the most important thing to recognize about the brainstem's blood supply is just how variable the vessels can be in size and position, but still provide adequate perfusion. This means that clinical syndromes produced by occlusion of a particular vessel are also variable. Patients whom you will encounter may present with fragments or combinations of syndromes.

Brainstem arteries in the medulla, pons and midbrain have similar patterns of distribution: 

• medial parts of the brainstem as far dorsal as the ventricle are supplied by long, slender penetrating branches called the paramedian branches
• dorsolateral parts of the brainstem are supplied by direct circumferential branchesof the vertebral or basilar arteries, or by branches of one of the major 'cerebellar' vessels as they curve around the brainstem on their way to the part of the cerebellum they supply. 

 

Clinical Note: Like the lenticulostriate branches of MCA, the paramedian vessels supplying the medial parts of the brainstem are at risk for hypertensive damage, particularly in the pons. Large pontine hemorrhages classically involve the corticospinal tracts and reticular formation bilaterally. Pontine lacunar infarcts may also damage the corticospinal tracts.

 

The blood supply of the medulla is derived from the two vertebral arteries. The midline anterior spinal artery, formed from the fusion of medial branches from each vertebral, supplies part of the central medulla (as well as much of the upper cervical cord). From its lateral side each vertebral gives off a variable branch, the posterior inferior cerebellar artery (PICA).  PICA has a complicated looping course as it swings out around the inferior olives, and runs along the dorsal lateral surface of the medulla before turning laterally and supplying the inferior surface of the cerebellum. The vertebral arteries fuse at the junction between the medulla and the pons to form the single midline basila artery which then proceeds rostrally along the surface of the anterior pons. The basilar artery also gives rise to additional large lateral vessels, most importantly, the anterior inferior cerebellar arteries and the superior cerebellar arteries.

The three major cerebellar vessels supply the posterior inferior, anterior inferior, and superior surfaces of the cerebellum respectively. The superior cerebellar artery also sends small branches penetrating deeply into the deep nuclei of the cerebellum.

Clinical Note: Although it is less common, the penetrating cerebellar vessels are also at risk for hypertensive hemorrhage, with bleeding often occurring near the dentate nucleus. Such a cerebellar hemorrhage can produce deficits related to the cerebellum such as postural instability or limb ataxia. It may also affect brainstem function by compression or by rupture into the fourth ventricle.