In 1938 Fischer, described five internal carotid artery segments in the opposite direction to the blood flow 1).
These segments were based on the angiographic course of the intracranial ICA rather than its arterial branches or anatomic compartments. Subsequent attempts to apply modern nomenclature to these numerical segments failed to recognize Fischer's original intent of describing patterns of arterial displacement by tumors and, therefore, resulted in a nomenclature that was anatomically inaccurate. Fischer's system was further limited, because segments were numbered opposite the direction of blood flow and the extracranial ICA was excluded 2).