Newly developed twisted carotid bifurcation on the left side incidentally diagnosed by magnetic resonance angiography

We herein report a case of left twisted carotid bifurcation (TCB) that newly appeared on follow-up examination. The patient was a 71-year-old woman with neck bruit and hyperlipidemia underwent neck magnetic resonance angiography. The left carotid bifurcation showed a normal branching pattern. Two years later, a follow-up examination was performed, and the left internal carotid artery (ICA) ran medial to the external carotid artery (ECA), indicating TCB. On the right side, the ICA ran dorsal to the ECA. The prevalence of TCB is reported to be 3.6%-15.1%. According to a review of the relevant literature, >80% of TCBs were found on the right side. TCB is generally considered to be a result of excessive lateral migration of the ECA during embryogenesis, and age-related atherosclerotic elongation and tortuosity of the carotid arteries may be another cause. In the case of TCB, carotid endarterectomy (CEA) is slightly difficult and slightly dangerous, because the affected ICA lies behind the ECA, and superior laryngeal nerve injury rarely occurs. TCB is not uncommon, but there is greater frequency on the right side. It may also newly develop. It is important to conduct a radiological evaluation of TCB before performing CEA.