ABSTRACT
Collateral circulation in the brain compensates for obstruction to arterial inflow or venous drainage (1). Descriptions of collateral vessels date back to the founding of neurology. Centuries after Sir Thomas Willis described arterial collaterals and their potential significance in disease, angiography illustrated the influential role of these routes. Hemodynamic studies later emphasized the critical impact of collaterals, yet subsequent imaging advances diverted attention away from angiography, seeking neuroprotection and targeting tissue ischemia. In the routine clinical practice of interventional neuroradiology, arterial and venous intracranial collaterals are influential factors in the diagnosis, treatment, and prognosis of various cerebrovascular disorders.
