An infarct is an area of ischemic necrosis caused by occlusion of the vascular supply to the affected tissue. Infarction primarily affecting the heart and the brain is a common and extremely important cause of clinical illness. Roughly 40% of all deaths in the United States are a consequence of cardiovascular disease, with most of these deaths stemming from myocardial or cerebral infarction. Pulmonary infarction is a common clinical complication, bowel infarction often is fatal, and ischemic necrosis of distal extremities (gangrene) causes substantial morbidity in the diabetic population.
Arterial thrombosis or arterial embolism underlies the vast majority of infarctions. Less common causes of arterial obstruction include vasospasm, expansion of an atheroma secondary to intraplaque hemorrhage, and extrinsic compression of a vessel, such as by tumor, a dissecting aortic aneurysm, or edema within a confined space (e.g., in anterior tibial compartment syndrome). Other uncommon causes of tissue infarction include vessel twisting (e.g., in testicular torsion or bowel volvulus), traumatic vascular rupture, and entrapment in a hernia sac. Although venous thrombosis can cause infarction, the more common outcome is simply congestion; typically, bypass channels rapidly open to provide sufficient outflow to restore the arterial inflow. Infarcts caused by venous thrombosis thus usually occur only in organs with a single efferent vein (e.g., testis or ovary).
tion.Thus,infarctsmaybeeitherred (hemorrhagic) orwhite (anemic) andmaybeeitherseptic orbland.
(Fig.4.17A )occur(1)asaresultofvenousocclusions(suchasinovariantorsion);(2)inloosetissues(e.g.,lung)wherebloodcancollectininfarctedzones;(3)intissueswithdualcirculationssuchaslungandsmallintestine,wherepartial,albeit (B)Sharplydemarcatedpaleinfarctinthespleen(white infarct).
Fig. 4.17 Redandwhiteinfarcts.(A)Hemorrhagic,roughlywedge-shapedpulmonaryinfarct(red infarct).
ABthe painful condition called the bends (so named in the 1880s because the afflicted person arches the back in a manner reminiscent of a then-popular women’s fashion pose called the Grecian bend). Gas bubbles in the pulmo inadequateperfusionbycollateralarterialsuppliesistypical;(4)inpreviouslycongestedtissues(asaconsequenceofsluggishvenousoutflow);and(5)whenflowisreestablishedafterinfarctionhasoccurred(e.g.,afterangioplastyofanarterialobstruction).
White infarcts occurwitharterialocclusionsinsolidorganswithend-arterialcirculations(e.g.,heart,spleen,andkidney),andwheretissuedensitylimitstheseepageofbloodfromadjoiningpatentvascularbeds(
Fig.4.17B ).Infarctstendtobewedge-shaped,withtheoccludedvesselattheapexandtheorganperipheryformingthebase(
Fig.4.17 );whenthebaseisaserosalsurface,thereisoftenanoverlyingfibrinousexudate.Lateralmarginsmaybeirregular,reflectingflowfromadjacentvessels.Themarginsofacuteinfarctstypicallyareindistinctandslightlyhemorrhagic;withtime,theedgesbecomebetterdefinedbyanarrowrimofhyperemiaattributabletoinflammation.
Fig.4.17B ).Bycomparison,hemorrhagicinfarctsaretheruleinthelungandotherspongyorgans(