Dear editor,
A 45-year-old Japanese woman was admitted to the hospital with a headache. Incidentally, an asymptomatic vascular anomaly was revealed. A left common carotid bifurcation was detected at the C7 level on the computed tomography angiography (Figure 1A) and digital subtraction angiography (Figure 1B), and its location was extremely proximal. The carotid canal on the left side (red arrow) was smaller than that on the right side (Figure 1C). The left internal carotid artery was hypoplastic and traveled the normal route. This suggested that it was a hypoplastic true internal carotid artery. The left middle cerebral artery was narrow, and the peripheral area was perfused via anastomosis. She had no family history of other skeletal or vascular anomalies. Klippel–Feil syndrome is known to cause the proximal location of common carotid bifurcation, but the patient had no relevant clinical findings. Although there are racial differences, the position of the bifurcation of the common carotid artery has been located around the C3 level in Japanese people (1). A low bifurcation of the common carotid artery has been shown to be associated with the persistence of the ductus caroticus, which is a segment of the dorsal aorta that connects the third and fourth aortic arches (2). It disappears with development and is not involved in normal blood vessel formation. There has only been one case of internal carotid artery hypoplasia on the right side (3). This is the first case of internal carotid artery hypoplasia on the left side and is important for blood vessel development. Anatomical knowledge of the common carotid artery bifurcation is essential for carotid endarterectomy and other invasive procedures.
