Absent Internal Carotid Artery With Intact Circle of Willis

The internal carotid arteries are one of the primary suppliers of the Circle of Willis and cerebral blood flow, but the rare case of agenesis of the internal carotid artery can impair the functional redundancies of cerebral blood supply. In this study, routine, medical education-focused cadaveric dissection of an 80-year-old male cadaver (cause of death was ventricular tachycardia) was performed. A case of agenesis of the left internal carotid artery and the carotid canal was identified. Upon investigation, we found that the compensatory pattern of irrigation in the Circle of Willis did not conform to previously described cases in the scientific literature. Further literature review suggested that such agenesis can be associated with a wide range of conditions from stroke, migraine, tinnitus, and Horner's syndrome. Due to the altered blood flow pattern, we caution the reading physician regarding the potential for ischemia and iatrogenic damage, particularly of the pituitary gland and eye. We suggest the use of neuroangiographic imaging in cases of agenesis of an internal carotid artery.