Pathology of the urinary system

2) Renal Infarcts

 

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the kidney has a particular predisposition to infarction because of the normally abundant blood flow 

through this organ and because of the pattern of its vascular perfusion, which is of a terminal or 

“end-artery” type: arcuate arteries originating from individual interlobar arteries at the level of the 

corticomedullary junction do not communicate with vessels from other interlobar arteries; there is 

therefore little opportunity for collateral blood circulation; 

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renal infarcts have a typically triangular (wedge) shape due to thrombosis / thromboembolism of 

renal vessels  

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 renal tissue undergoes coagulative necrosis; this can be accompanied by suppuration 

and abscessation if the material causing thrombosis is infected by bacteria; 

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the size of the infarct depends on the size of the affected vessel; obstruction of an arcuate artery 

results in necrosis of a wedge of both cortex and medulla, whereas obstruction of an interlobular 

artery results in necrosis of a wedge of cortex only; 

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acute infarcts are often swollen and dark red because of hemorrhage; older infarcts appear pale, 

following red blood cell lysis/removal, and may be rimmed by a thin zone of hyperemia; this gradual 

change in color may take only a few (2-4) days; 

 

The concept of terminal or “end-artery” vascular perfusion in the kidney is relative.  There is 

always some degree of connection among capillaries.  As a portion of the renal tissue 

undergoes ischemic necrosis as a result of infarction, blood vessels in the affected area die 

together with the parenchyma.  This allows red blood cells to escape from the intravascular 

compartment, including some coming from the relatively few capillaries outside the infarcted 

area that are anastomosed with the affected blood vessels.  This escape of red blood cells 

(and thus hemorrhage) is limited and does not last long because of the little collateral 

circulation available but is sufficient to result in grossly visible hemorrhage.  The latter, 

however, fades away quickly because of hemolysis of red blood cells (“white infarct” in the 

human literature). [Conversely, in other organs characterized by abundant collateral 

circulation, such as lung and intestine, infarction of a portion of the tissue caused by arterial 

occlusion typically appears as a persistently severe area of hemorrhage (“red infarct” in the 

human literature).] 

 

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chronic infarcts heal by fibrosis, causing the tissue to retract and form depressions on the outer 

surface of the renal cortex; 

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valvular endocarditis of the left side of the heart (mitral or aortic valves) is the most common cause 

of renal infarcts; most commonly seen in cattle and pigs.