Collateral circulation maintains cerebral blood flow in the setting of arterial occlusion. Trans-cranial Doppler (TCD) can detect some of these collateral circulations by providing real-time information about the direction and the velocity of blood flow. The circle of Willis is the main intracranial collateral pathway. The anterior communicating artery and the posterior communicating arteries are the most important component of the Willisian collaterals and also called first order collaterals. Second order collaterals are ophthalmic artery and leptomeningeal collaterals which considered as a reserve system. This article reviews the collateral pathways which can be detected by TCD and clinical significance of those.

Journal of Neurosonology 6(1):1-5, 2014
Key Words: Transcranial doppler, Collateral circulation