The absence of the internal carotid artery: report of two cases.

The absence of the internal carotid artery (ICA) is a very rare anomaly. Since the first description of the condition in 1787, only 60 cases have been reported in the literature. We report two cases of absence of the left ICA amongst 2195 carotid angiograms performed in the Department of Neuroradiology at the Royal Brisbane Hospital over a period of 4 years. The first patient was suffering from obstructive hydrocephalus; the second from right cerebellopontine angle syndrome. Cerebral angiography by catheterization of the aorta revealed the absence of the left ICA. The collateral circulation to the left cerebral hemisphere was provided by the vertebrobasilar system via a dilated left posterior communicating artery. In the first patient, the absence of the ICA was coincidental with other congenital anomalies of the cervico-occipital junction. In the second patient, the dilated vertebrobasilar system was responsible for compressing the right cranial nerves VII and VIII. It is emphasized that in some cases of cerebellopontine angle syndromes, thorough investigation of the cerebral vessels is necessary.