Ischemia after carotid endarterectomy: Comparison between transcranial Doppler sonography and diffusion-weighted MR imaging

BACKGROUND AND PURPOSE: Hyperintense signals on diffusion-weighted MR image s (DWIs) are believed to correspond accurately with cerebral ischemic event s. Intraoperative transcranial Doppler sonography (TCD) can reveal hemodyna mic and embolic events during carotid endarterectomy (CEA), Our purpose was to determine whether the occurrence of hyperintense signals on postoperati ve DWIs corresponds to intraoperative embolic or hemodynamic events, METHODS: Seventy-seven CEAs were monitored intraoperatively with TCD to rec ord blood flow velocity changes after cross clamping to ascertain the prese nce of adequate collateral flow and to record microembolic signals, DWI was used to classify the hemisphere ipsilateral to the CEA by type: 0, no lesi ons (n = 51); I, cortical lesions only (n = 2); II, subcortical white matte r lesions only (n = 6); III, mixed type with cortical and subcortical lesio ns (n = 11); IV, large territorial infarcts (n = 6); and V, other types of lesions (n = 1), RESULTS: Neither the five clinical events (one transient ischemic attack, t wo minor strokes, and two major strokes) nor any DWI type (I-V) showed at r elationship to blood velocity decreases after cross clamping or, in patient s who were selectively shunted, to total ischemic time necessary for shunt insertion and removal, Total microembolic signal count was significantly hi gher in the five CEAs with clinical events than in those without, It was al so higher on the DWIs showing a hyperintense lesion as compared with DWIs s howing no lesion. CONCLUSION: Apart from lesions corresponding to clinical deficits, CEA is a ssociated with a substantial number of small areas of brain tissue at risk for irreversible ischemia, The main cause of intraoperative stroke seems to be embolism, suggesting that microembolic signals in CEA are highly releva nt events for brain tissue.