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. 2001 Oct;22(9):1704-10.

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

F Caramia  1 , A Santoro, P Pantano, E Passacantilli, G Guidetti, A Pierallini, L M Fantozzi, G P Cantore, L Bozzao
Affiliations

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

F Caramia et al. AJNR Am J Neuroradiol. 2001 Oct.

Abstract

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 study was to use perfusion MR imaging to evaluate cerebral hemodynamics in such patients before and after extraintracranial high-flow bypass surgery.

Methods: Five patients with a giant aneurysm of the intracranial internal carotid artery underwent MR studies before, 1 week after, and 1 month after high-flow bypass surgery. We performed MR and digital subtraction angiography, and conventional and functional MR sequences (diffusion and perfusion). Surgery consisted of middle cerebral artery (MCA)-internal carotid artery bypass with saphenous vein grafts (n = 4) or MCA-external carotid artery bypass (n = 1).

Results: In four patients, MR perfusion study showed impaired hemodynamics in the vascular territory supplied by the MCA of the aneurysm side, characterized by significantly reduced mean cerebral blood flow (CBF), whereas mean transit time (MTT) and regional cerebral blood volume (rCBV) were either preserved, reduced, or increased. After surgery, angiography showed good canalization of the bypass graft. MR perfusion data obtained after surgery showed improved cerebral hemodynamics in all cases, with a return of CBF index (CBFi), MTT, and rCBV to nearly normal values.

Conclusion: Increased MTT with increased or preserved rCBV can be interpreted as a compensatory vasodilatory response to reduced perfusion pressure, presumably from compression and disturbed flow in the giant aneurysmal sac. When maximal vasodilation has occurred, however, the brain can no longer compensate for diminished perfusion by vasodilation, and rCBV and CBFi diminish. Bypass surgery improves hemodynamics, increasing perfusion pressure and, thus, CBFi. Perfusion MR imaging can be used to evaluate cerebral hemodynamics in patients with intracranial giant aneurysm.

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Figures

<sc>fig</sc> 1.
fig 1.
Patient with a giant intracranial aneurysm of the left internal carotid artery (patient 2). A, Maps of rCBV (top left), CBFi (top right), MTT (bottom left), and TTP (bottom right) before surgery. The MTT and TTP maps show a large hyperintense area on the left hemisphere compared with the contralateral (mean asymmetry index ± SD, 1.46 ±.0.34), indicating slower transit time in the side of the aneurysm. The CBFi maps show reduced flow in the same region (asymmetry index, 0.73 ± 0.09), whereas the rCBV maps show a minimal increase (asymmetry index, 1.13 ± 0.11). This hemodynamic pattern, characterized by a mismatch between flow and volume, can be explained as a vasodilatory response of the brain to a decrease in perfusion pressure. B, Maps of rCBV (top left), CBFi (top right), MTT (bottom left), and TTP (bottom right) after extra-intracranial bypass surgery. Temporal parameter maps (MTT and TTP) in the left hemisphere are only slightly elevated compared with the contralateral side (asymmetry index 1.23 ± 0.44), especially in the posterior region. The CBFi and rCBV asymmetry indices are only minimally altered (asymmetry index of CBFi, 0.91 ± 0.08; of rCBV, 1.11 ± 0.32). C, Postoperative T2-weighted images show the large aneurysmal sac, which is hyperintense, suggesting absence of flow due to exclusion from circulation.
<sc>fig</sc> 2.
fig 2.
Mean asymmetry indices (±SD) for rCBV, CBFi, and MTT from MR studies performed in five patients before, 1 week after, and 1 month after bypass surgery. Bars represent the mean values of each of the three variables calculated in all patients: a indicates significantly lower values on the affected side than on the contralateral side (P = .0001); b indicates postoperative asymmetry indices significantly higher than the preoperative values (P < .05)
<sc>fig</sc> 3.
fig 3.
Mean asymmetry indices (± SD) for rCBV, CBFi, and MTT in five patients with intracranial aneurysm before surgery. Bars represent the mean asymmetry index of each of the three variables calculated in single patients
See this image and copyright information in PMC

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