Blood Supply and Venous Drainage of the Brain

Question 1

Describe the posterior circulation of the brain:

Answer 1

Main Arteries:

Vertebral Arteries - arise from the subclavian arteries, ascend via transverse foramina of cervical vertebrae, and enter the cranium via the foramen magnum.

Basilar Artery - formed by the union of vertebral arteries; bifurcates into posterior cerebral arteries (PCAs)

Supplies:
Posterior 1/3 of the brain: occipital lobes, brainstem, cerebellum, and medial temporal lobes.

Question 2

Describe the anterior circulation of the brain:

Answer 2

Main Arteries:

Internal Carotid Arteries (ICA): Enter the cranium via the carotid canal and contribute to the Circle of Willis.

Branches:

• Anterior Cerebral Arteries (ACA): Supply the medial frontal and parietal lobes.
• Middle Cerebral Arteries (MCA): Supply the lateral aspects of the frontal, parietal, and temporal lobes.

Supplies:
Anterior 2/3 of the brain, including most of the cerebrum

Question 3

Describe the Cerebral Arterial Circle (Circle of Willis)

Answer 3

A circular anastomosis at the base of the brain, surrounding the optic chiasm and pituitary stalk

Formed by:

-Anterior Circulation: Internal carotid arteries, ACA, and anterior communicating artery (AComm).
- Posterior Circulation: Posterior cerebral arteries (PCA) and posterior communicating arteries (PComm)

Function - provide collateral blood flow in case of arterial occlusion

Question 4

Describe the venous drainage of the brain:

Answer 4

Superficial Veins - drain the cortex and empty into dural venous sinuses.

Deep Veins - drain deep brain structures (e.g., internal cerebral veins), converging into the great cerebral vein (of Galen)

Drainage pathway:

Blood flows from dural venous sinuses → internal jugular veins → systemic circulation

Question 5

Describe the dural venous sinuses:

Answer 5

Spaces between the outer and inner layers of the dura matter
Lead to the internal jugular vein
Diploic veins from bone & emissary veins from outside cranial cavity also drain into venous sinuses

Question 6

Describe the different types of dural venous sinuses:

Answer 6

Superior sagittal sinus –
receives blood from superior cerebral veins, diploic, emissary and falx cerebri veins

Inferior sagittal sinus – cerebral veins & falx cerebri veins. Joined by great cerebral vein and forms straight sinus

Straight Sinus - connects inferior sagittal sinus to the confluence of sinuses

Transverse Sinuses - drain blood laterally from the confluence of sinuses to sigmoid sinuses

Sigmoid Sinuses - drain into the internal jugular vein

Question 7

Describe the cavernous sinuses:

Answer 7

Paired venous sinuses on either side of the sella turcica, surrounding the pituitary gland

Receive blood from cerebral,
ophthalmic & emissary veins

Structures passing through - Internal carotid artery, cranial nerves III, IV, V1, V2, and VI

Venous connections with the facial vein make the cavernous sinus susceptible to infection from the danger triangle

Question 8

What is the danger triangle ?

Answer 8

Area of the face (corners of the mouth to the bridge of the nose) with venous connections to the cavernous sinus via the ophthalmic veins

Infections in this region (e.g., acne, cellulitis) can spread to the cavernous sinus, causing cavernous sinus thrombosis, a potentially life-threatening condition

Question 9

Describe the superior petrosal sinuses and basilar sinus:

Answer 9

Superior petrosal sinuses:

• drain the cavernous sinuses into transverse sinuses
• receives blood from cerebral & cerebellar veins
• Inferior petrosal sinuses assist draining cavernous sinuses

Basilar sinus - Connects the inferior petrosal sinuses to each other and to the vertebral plexus of veins