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Cerebral Hemodynamics on MR Perfusion Images before and after Bypass Surgery in Patients with Giant Intracranial Aneurysms

Francesca Caramiaa, Antonio Santoroa, Patrizia Pantanoa, Emiliano Passacantillia, Giulio Guidettia, Alberto Pierallinia, Luigi Maria Fantozzia, Gian Paolo Cantorea and Luigi Bozzaoa

a From the Neuroradiology (F.C., P.P., G.G., A.P., L.M.F., L.B.) and Neurosurgery Sections (A.S., E.P., G.P.C.), I and II (L.M.F.) School of Medicine, University of Rome "La Sapienza"; and IRCCS Neuromed (L.B.), Pozzilli, Italy.



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  		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.



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  		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)



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  		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





Copyright © 2009 by the American Society of Neuroradiology. Print ISSN: 0195-6108 Online ISSN: 1936-959X