A 68-YEAR-OLD woman was admitted to our clinic for a slowly progressive gait disturbance. Her medical record was unremarkable. There was no history of transient ischemic attacks or stroke. During the examination, she was alert and oriented and had no focal neurologic deficit. She was afebrile with a blood pressure reading of 124/82 mm Hg, and results of routine laboratory tests were normal. Magnetic resonance imaging revealed convoluted vascular flow voids around the right cavernous sinus (Figure 1). A contrast-enhanced computed tomographic scan indicated hypoplasia of the right carotid canal and complete aplasia of the left carotid canal (Figure 2). Cavernous portions of the bilateral internal carotid arteries were not visible. A 3-dimensional computed tomographic scan of the bone window demonstrated an anomalous, calcified, dolichoectatic cerebral artery (Figure 3). Right carotid angiography revealed obstruction of the right internal carotid artery at its origin (Figure 4). Numerous small vessels originating from the external carotid artery made multiple anastmoses to the carotid siphon, through which the cerebral circulation was maintained (Figure 5). These findings were compatible with carotid rete mirabile. Catheterization to the left common carotid artery and bilateral vertebral artery was not possible because of the associated aortic arch anomaly, that is, the right aortic arch with an aberrant left innominate artery originating from the proximal descending aorta (Figure 6). The patient has been observed for a year without treatment and is clinically stable.