CT SCAN OF THE SKULL BASE IN INTERNAL CAROTID-ARTERY HYPOPLASIA

Internal carotid artery (ICA) hypoplasia is a rare congenital anomaly that is sometimes difficult to distinguish from acquired diseases asso ciated with narrowing of the ICA. As the carotid canal develops in ass ociation with the ICA, a hypoplastic carotid artery should result in a hypoplastic carotid canal. We used skull base CT scans to measure the size of carotid canals in 4 patients with ICA hypoplasia (bilateral i n 1) and in 30 consecutive controls. The diameter of the carotid canal was significantly smaller in the patients with carotid hypoplasia (2. 4-3.0 mm, on the involved side) than in the controls (mean = 6.4 +/- 0 .8 mm, range = 5.2-9.8 mm) with no overlapping value (p < 0.001). The ratio of the largest to the smallest carotid diameter was greater than 2 in patients with unilateral hypoplasia, while it never exceeded 1.2 in controls. CT scan of the skull base is a simple and reliable tool for confirming the diagnosis of ICA hypoplasia.