Cerebral hemodynamics on MR perfusion images before and after bypass surgery in patients with giant intracranial aneurysms

BACKGROUND AND PURPOSE: Preoperative assessment of the anatomy and dynamics of cerebral circulation for patients with giant intracranial aneurysm can improve both outcome prediction and therapeutic approach. The aim of our st udy was to use perfusion MR imaging to evaluate cerebral hemodynamics in su ch patients before and after extraintracranial high-flow bypass surgery. METHODS: Five patients with a giant aneurysm of the intracranial internal c arotid artery underwent MR studies before, I week after, and 1 month after high-flow bypass surgery. We performed MR and digital subtraction angiograp hy, and conventional and functional MR sequences (diffusion and perfusion). Surgery consisted of middle cerebral artery (MCA)internal carotid artery b ypass with saphenous vein grafts (n = 4) or MCA-external carotid artery byp ass (n = 1). RESULTS: In four patients, MR perfusion study showed impaired hemodynamics in the vascular territory supplied by the MCA of the aneurysm side, charact erized by significantly reduced mean cerebral blood flow (CBF), whereas mea n transit time (MTT) and regional cerebral blood volume (rCBV) were either preserved, reduced, or increased. After surgery, angiography showed good ca nalization of the bypass graft. MR perfusion data obtained after surgery sh owed improved cerebral hemodynamics in all cases, with a return of CBF inde x (CBFi), MTT, and rCBV to nearly normal values. CONCLUSION: Increased MTT with increased or preserved rCBV can be interpret ed as a compensatory vasodilatory response to reduced perfusion pressure, p resumably from compression and disturbed flow in the giant aneurysmal sac. When maximal vasodilation has occurred, however, the brain can no longer co mpensate for diminished perfusion by vasodilation, and rCBV and CBFi dimini sh. Bypass surgery improves hemodynamics, increasing perfusion pressure and , thus, CBFi. Perfusion MR imaging can be used to evaluate cerebral hemodyn amics in patients with intracranial giant aneurysm.