Hemodynamic significance of abnormal magnetic resonance angiography findings assessed by acetazolamide-challenged brain perfusion SPECT

Objectives Luminal narrowing of carotid or cerebral artery is occasionally observed on MR angiography (MRA), although a considerable proportion are non-pathogenic. In this study, we assessed the hemodynamic significance of abnormal MRA findings using with brain perfusion SPECT by visual and statistical probabilistic anatomical mapping (SPAM) analysis.

Methods A total of 118 patients who underwent acetazolamide-challenged brain SPECT with abnormal MRA findings were retrospectively enrolled. MRA findings were classified according to stenosis severity, and vessel involvement: Group 1 no stenosis; Group 2 mild to moderate (<75% narrowing of luminal diameter) single vessel stenosis in ICA or MCA; Group 3, severe single vessel stenosis in ICA or MCA; Group 4 multi-vessel stenoses of the ICA and MCA. SPECT images were assessed for cerebral vascular reserve (CVR) and graded visually into 0-3. CVR index (CVRI) was calculated using an automated quantification method based on SPAM.

Results Among the 236 MCA territories evaluated of 118 patients, 87 were classified under Group 1 and only 2 (2%) showed impaired CVR. In Groups 2 and 3, 17/80 (21%) and 29/57 (51%) MCA territories showed impaired CVR. Mean CVR visual grade was 0.3 and 0.8, respectively. In Group 4, 100% of the MCA territories showed impaired CVR, with mean visual grade of 1.5. There was significant difference of impairment proportion between groups (p<0.001). CVRI calculated on SPAM was in excellent correlation with visual grading for CVR. Significant difference was also observed according to the groups: Group 1, 2.1; Group 2, 0.1; Group 3, -4.9; Group 4, -8.7(p<0.001).

Conclusions The risk of impaired CVR in case of single stenosis in ICA or MCA was correlated with stenosis severity: 20% in mild to moderate, and 51% in severe stenosis. However, patients with stenoses in both the ICA and MCA, regardless of severity, had a very high risk for CVR impairment