Brainstem compression by basilar artery anomalies as visualized by MRI.

The use of MRI in the diagnosis of vascular anomalies of the basilar artery is demonstrated in two cases. The first patient had a partially thrombosed giant aneurysm of the basilar artery; the second had an atypical course of the basilar artery. MRI is indicated whenever other imaging procedures do not provide a definite diagnosis or the use of contrast medium for conventional X-ray examination or computed tomography is contraindicated.