Segmental atelectasis and postoperative reperfusion edema could be causes of new perfusion scan defects in our patient population. Both pulmonary parenchymal abnormalities have been reported to induce regional decrements in flow. However, the steal zones have been consistently free of parenchymal infiltrates or areas of collapse on the postoperative chest roentgenograms; the postoperative ventilation scans have shown no abnormality in these segments; and, as previously reported, reperfusion edema is limited to zones of lung served by endarterectomized vessels, whereas steal occurs dominantly in untouched segments.
What alternative possibilities exist? A brief note regarding the approach to endarterectomy may provide some insight. Arteries are not endarterectomized under two circumstances: when no chronic thrombus is visible in the lobar or segmental artery at surgery; or when thrombus is seen, but is too thin to allow dissection to the segmental level. In addition, despite careful attempts at endarterectomy, the specimen may break distally, leaving behind obstructing organized thrombus in some segmental or subsegmental vessels. buy cipro
Given these considerations, we can put forth two different explanations for the postoperative regional decrement in flow responsible for the steal. First, in some cases, partially occluding thrombus may remain after surgery either because it was too distal to allow removal or, as noted above, “broke off’ at endarterectomy. However, the presence of partially occlusive residual distal thrombi—as seen on the preoperative arteriogram—appears to explain the steal phenomenon in a small minority of patients.
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