Figure 11. Dolichoectasia of the vertebral or basilar arteries may result in vascular compression of the trigeminal nerve. (a) Coronal plane STIR image at the level of the pons. The ectatic basilar artery is seen as a flow void (long arrow) displacing the left trigeminal nerve superiorly and laterally (short arrow). (b) Parasagittal reconstruction of a 3D-FISP sequence in the plane of the left trigeminal nerve. The ectatic vessel is shown as a high signal intensity structure (long arrow) impinging on the trigeminal nerve (arrowhead).