Exclusively Posterior Circulation Stroke Caused by Internal Carotid Artery Thrombosis.

A fetal posterior cerebral artery (FPCA) is an anatomic variant in which the posterior cerebral artery (PCA) is an embryological derivative of the internal carotid artery (ICA). Patients with FPCA may experience posterior circulation stroke (PCS) after a thrombotic event in the ICA system, while exclusively PCS caused by thrombosis of the ICA has rarely been reported. We report a patient with FPCA and summarize 3 types of exclusively PCS caused by FPCA due to thrombotic events in the ICA system. Type A: the thrombus involves the opening of the FPCA and obstructs the blood flow of the entire ICA. The contralateral ICA compensates the ipsilateral middle cerebral artery (MCA) and anterior cerebral artery (ACA) through the anterior communicating artery (ACOM). Type B: the thrombus involves the opening of the FPCA but does not block the blood flow of the entire ICA, which still perfuses the ipsilateral ACA and MCA. Type C: the thrombus only involves the FPCA and not the ipsilateral ICA. Patients with types A and B may obtain a good prognosis through endovascular treatment (EVT), while the benefits of this procedure in type C patients are unclear.