MRI of vertebrobasilar disecting aneurysms: diagnostic value and pitfalls of spin-echo sequences

Magnetic resonance imaging (MRI) features of 12 cases with vertebrobasilar dissecting aneurysms (VBDA) were compared with those of 80 cases with nondissecting aneurysms (NDA). Seven patients with VBDA showed an eccentrically narrowed true lumen adjacent to the semilunar clot in the false lumen. Such findings were also found in patients with thrombosed NDA. However, the segment of the mural haematoma was longer in those with VBDA. An intimal flap was detected in only 3 cases of VBDA. Two patients with VBDA showed only iso- or high signal intensity of the vertebral artery; therefore, differentiation from obstruction of the vertebral artery was difficult. Flow-dependent spatial misregistration, seen adjacent to the normal vessels, sometimes mimics intramural haematoma.