Pathologic Findings Light Microscopy

Fibrin and platelet thrombi are present, primarily in the glomeruli (1-4). Fibrin is best visualized on hematoxylin and eosin or silver stains. Lesions may extend to arterioles, with some overlap with progressive malignant hypertension and systemic sclerosis, where arteriolar and even larger vessel involvement occurs (Figs. 11.1 and 11.2). Mesangiolysis occurs frequently, but is a focal, subtle lesion that may be overlooked (11). Mesangial areas seem to "unravel," resulting in very long, sausage-shaped capillary loops due to the loss of mesangial integrity and coalescence of adjoining loops.

Figure 11.1. Segmental red blood cells (RBCs) and fibrin in capillary loops and arteriole in glomerulus in thrombotic microangiopathy (Jones silver stain).

In infants and young children, thrombotic lesions predominate (4). In older children and adults, varied lesions occur. Many glomeruli may show only ischemic changes with corrugation of the glomerular basement membrane and retraction and collapse of the glomerular tuft. Segmental glomerular necrosis may be seen with rare well-developed fibrin thrombi. Arterioles and arteries, when involved, show thrombosis and sometimes necrosis of the vessel wall, with intimal swelling, mucoid change and intimal proliferation. Fragmentation of red blood cells within the vessel wall may also be seen. Tubular and interstitial changes are proportional to the degree of glomerular changes. In severe cases, cortical necrosis can be seen (12).

Secondary changes late in the course include glomerular sclerosis, either segmental or global. Reduplication of the glomerular basement membrane may occur in the late phase due to organization following endothelial injury.

Figure 11.2. Entire glomerulus and arteriole are filled with chunky, eosinophilic fibrin in this case of hemolytic uremic syndrome (HUS) (Jones silver stain).

Figure 11.3. Fibrin tactoids in subendothelial area in thrombotic microangiopathy (electron microscopy).

Figure 11.3. Fibrin tactoids in subendothelial area in thrombotic microangiopathy (electron microscopy).

Blood Pressure Health

Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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