Rare variant of internal carotid artery anatomy

Three-dimensional maximum intensity projection (MIP) image shows abrupt termination of cervical internal carotid artery (ICA) with a branch of external carotid artery (ECA) coursing in the distal expected course of ICA. (A) External carotid artery (ECA) (thin arrow) and internal carotid artery (ICA) (thick arrow) after bifurcation, (B) branch arising from ECA (curved arrow) can be seen between ECA and ICA (which gets further narrowed), (C) ICA gets narrowed as it courses cranially, (D) the branch arising from ECA continues along the course of ICA and ICA is not seen. Congenital absence of the ECA has been reported in literature.3 Professor Lasjaunias in his article proposed segmental concept of carotid artery—which states that ICA results from persistence of several embryologically different segments (ventral pharyngeal hyoid, mandibular, primitive maxillary, trigeminal, dorsal ophthalmic and ventral ophthalmic).4 He further stated that each segment may undergo agenesis independently and blood flow is established through the ICA distal to the agenetic segment.