Describe blood supply of brain stem and add a note on its applied importance.

Arterial Supply of the Brainstem

The arterial supply to the brainstem is a complex network derived from the vertebral and basilar arteries. These arteries are branches of the subclavian arteries.

1. Vertebral Arteries

The vertebral arteries ascend through the transverse foramina of the cervical vertebrae (C1-C6). They enter the skull through the foramen magnum and merge to form the basilar artery. Before merging, they give off several important branches:

• Posterior Inferior Cerebellar Artery (PICA): Supplies the inferior cerebellum, medulla oblongata (including the dorsal column nuclei and spinocerebellar tracts), and the posterior lateral medulla.
• Anterior Inferior Cerebellar Artery (AICA): Arises from the basilar artery but often receives collateral supply from the vertebral artery. Supplies the anterior inferior cerebellum and the lateral pons.
• Spinal Arteries: Anterior and posterior spinal arteries supply the spinal cord.

2. Basilar Artery

Formed by the union of the two vertebral arteries, the basilar artery ascends along the ventral surface of the pons. It terminates by bifurcating into the posterior cerebral arteries. Branches of the basilar artery include:

• Anterior Inferior Cerebellar Artery (AICA): (As mentioned above, often has contributions from both vertebral and basilar).
• Pontine Arteries: Numerous small branches supplying the pons, including the paramedian pontine arteries.
• Labyrinthine Artery (Internal Auditory Artery): Supplies the inner ear.
• Superior Cerebellar Artery (SCA): Supplies the superior cerebellum and the upper pons.

3. Specific Brainstem Regions and their Supply

Different regions of the brainstem receive blood supply from overlapping arterial territories, providing some degree of collateral circulation. However, this collateral circulation is often insufficient to prevent significant damage in cases of major arterial occlusion.

• Medulla Oblongata: Primarily supplied by the vertebral arteries (PICA) and branches from the anterior spinal artery.
• Pons: Supplied by the basilar artery (pontine arteries, AICA, SCA) and vertebral arteries.
• Midbrain: Supplied by branches of the posterior cerebral artery and the superior cerebellar artery.

Venous Drainage of the Brainstem

The venous drainage of the brainstem is complex and involves several venous sinuses and veins.

• Superior Petrosal Sinus: Drains the pons and midbrain.
• Inferior Petrosal Sinus: Drains the medulla oblongata and cerebellum.
• Internal Jugular Vein: Receives drainage from both superior and inferior petrosal sinuses.
• Vertebral Veins: Accompany the vertebral arteries and drain into the brachiocephalic veins.

Applied Importance: Clinical Correlations

Understanding the blood supply of the brainstem is critical for diagnosing and managing stroke syndromes. Occlusion of specific arteries leads to predictable clinical deficits:

• Wallenberg Syndrome (Lateral Medullary Syndrome): Resulting from PICA occlusion. Symptoms include vertigo, nausea, dysphagia, hoarseness, Horner’s syndrome (ipsilateral), and loss of pain and temperature sensation on the contralateral side of the body.
• Locked-In Syndrome: Often caused by basilar artery occlusion, resulting in quadriplegia, anarthria (inability to speak), and preserved consciousness with vertical eye movements and blinking.
• Pontine Strokes: Occlusion of pontine arteries can cause various deficits depending on the location of the infarct, including ataxia, paralysis, and sensory loss.

Furthermore, vascular malformations like arteriovenous malformations (AVMs) in the brainstem can present with seizures, headaches, and progressive neurological deficits. Accurate diagnosis and treatment planning require a thorough understanding of the vascular anatomy.