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Dr. Yasser Mokhtar, M.D.

3. Collateral blood supply of the brain

Fields et al. described this in 1985. The actual pattern of collateral blood flow depends on where the major vessels are stenosed or occluded and on which collateral channels are available and free from disease.

On the whole, the development of collateral channels is more effective if the major vessel occlusion occurs over weeks or months rather than suddenly. Collateral blood flow may develop via:

A. Extracranial connections:

  • In the orbit, branches of ECA anastomose with branches of ophthalmic artery.

  • Branches of ECA anastomose with branches of vertebral artery.

  • Branches of vertebral artery anastomose with branches of subclavian artery.

  • Branches of ECA anastomose with branches of subclavian artery.

B. Intracranial connections:

  • Circle of Willis

It is a network of blood vessels present at the base of the brain. This polygon of blood vessels is formed by the proximal parts of the two anterior cerebral arteries connected by the ACoA and the proximal parts of the two posterior cerebral arteries connected to the distal internal carotid arteries by the posterior communicating arteries. However fifty per cent of circles have hypoplastic or absent segments and the potential for collateral flow is not always as good as it might first appear.

  • Leptomeningeal anastomoses:

It lies on the surface of the brain. They develop between the cortical branches of the anterior, middle and posterior cerebral arteries.

  • Dural anastomoses

It occurs between meningeal branches of the ICA, ECA and the vertebral arteries.

  • Anterior choroidal artery

It is a branch of ICA can anastomose with the posterior choroidal artery

  • posterior choroidal artery

A branch of ECA (Fields et al., 1985). 

4. Venous drainage

Venous blood flows peripherally via superficial cerebral veins and centrally via the deep cerebral veins into the venous sinuses (which lie between the outer endosteal and the inner meningeal layer of the dura) which drain into the internal jugular vein. The cerebral veins are thin walled and have no valves. There are numerous venous connections between cerebral veins and dural sinuses and venous systems of the meninges, skull, scalp and nasal sinuses so facilitating propagation of thrombus or spread of infection between these vessels (Sheldon 1981).

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