Lines of Zahn
Summary
Lines of Zahn are alternating pale layers of platelets and fibrin with darker layers of red blood cells seen grossly and microscopically in a thrombus. They indicate a thrombus that formed in flowing blood, and so distinguish an antemortem thrombus from a postmortem clot.
Detail
Lines of Zahn arise because a thrombus growing in moving blood lays down platelets and fibrin in pale bands, separated by darker bands of trapped erythrocytes. Their presence proves the thrombus formed while circulation was still active, which is why they are the classic answer to distinguishing an antemortem thrombus from a postmortem clot; the latter is gelatinous, has a 'chicken fat' yellow upper layer over a 'currant jelly' red dependent layer, and lacks lamination. Lines of Zahn are most obvious in thrombi from areas of rapid flow such as the heart chambers and the aorta, and are subtle or absent in thrombi formed in sluggish venous blood. They are a favourite board question in the context of sudden cardiac death, mural thrombus over a myocardial infarct, and pulmonary thromboembolism.
Sources
- First Aid for the USMLE Step 1
- Robbins Basic Pathology
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