Dilated outer diameter of the dissected artery: acute bilateral anterior cerebral artery dissection evaluated by repeat magnetic resonance cisternography. Case report.

A 42-year-old male patient presented with an anterior cerebral artery (ACA) dissection manifesting as sudden onset of severe headache. Initial computed tomography revealed faint subarachnoid hemorrhage in the frontal region. Initial angiography showed tapering stenosis at the A(2) segment of right ACA. The patient was admitted to our hospital and treated conservatively. Magnetic resonance (MR) imaging and angiography did not detect intramural hematoma, intimal flap, or double lumen at the stenotic right A(2) segment. The ACA dissection was difficult to confirm based on the findings on day 0. ACA dissection was confirmed by improvement of the right ACA stenosis on follow-up angiography on day 14. On the other hand, MR cisternography revealed a fusiform dilatation of the vascular outer contour at the right A(2) on day 0, which had resolved on day 14. Cerebral angiography and MR cisternography similarly suggested asymptomatic contralateral (left) A(2) dissection on day 14. Fusiform dilatation of the vascular outer contour at the affected segment on MR cisternography may be indicative of arterial dissection in the acute phase.