6 infarction

INFARCTIONINFARCTION

Dr.CSBR.Prasad, M.D.

Common clinical examples of Common clinical examples of infarction:infarction:

• Myocardial infarction• Cerebral infarction• Pulmonary infarction• Gangrene of limbs

Atrial fibrillation Atrial fibrillation with mural thrombiwith mural thrombi

INFARCTIONINFARCTION

Def: An infarct is an area of ischemic necrosis caused by

occlusion of either the arterial supply or the venous drainage in a

particular tissue

Basis of infarction:Basis of infarction:

Vascular compromise• Obstruction to arterial supply • Impeded venous drainage

Common causes:Common causes:Arterial occlusion:Arterial occlusion:

• 99% result from arterial occlusion (thrombotic or embolic events)• Other causes:

local vasospasmexpansion of an atheroma (hemorrhage within a plaque) extrinsic compression of a vessel (e.g., by tumor)twisting of the vessels (e.g., in testicular torsion or bowel

volvulus)compression of the blood supply by edema or by entrapment in a

hernia sactraumatic rupture of the blood supply

Venous occlusion:Venous occlusion: (organs with single veinous out flow)• Thrombosis

Classification Classification Based on the colour & presence or absence of

infection

MorphologyMorphologyRed (hemorrhagic) infarctsRed (hemorrhagic) infarcts occur (1) with venous occlusions (such as in ovarian torsion); (2) in loose tissues (such as lung), which allow blood to

collect in the infarcted zone; (3) in tissues with dual circulations (e.g., lung and small

intestine), permitting flow of blood from the unobstructed vessel into the necrotic zone (obviously such perfusion is not sufficient to rescue the ischemic tissues);

(4) in tissues that were previously congested because of sluggish venous outflow; and

(5) when flow is re-established to a site of previous arterial occlusion and necrosis (e.g., following fragmentation of an occlusive embolus or angioplasty of a thrombotic lesion) 

MorphologyMorphology

White (anemic) infarctsWhite (anemic) infarcts occur with arterial occlusions in solid organs with

end-arterial circulation (such as heart, spleen, and kidney), where the solidity of the tissue limits the amount of hemorrhage that can seep into the area of ischemic necrosis from adjoining capillary beds

Most of the infarcts are wedge Most of the infarcts are wedge shapedshaped

• with the occluded vessel at the apex and the periphery of the organ forming the base

• when the base is a serosal surface, there is often an overlying fibrinous exudate.

• The lateral margins may be irregular, reflecting the pattern of vascular supply from adjacent vessels.

Margins become hyperemicMargins become hyperemic

• Initially:Initially: all infarcts are poorly defined and slightly hemorrhagic

• Later:Later: margins tend to become better defined by a narrow rim of hyperemia attributable to inflammation at the edge of the lesion.

Examples of infarcts:

A, Hemorrhagic, roughly wedge-shaped pulmonary infarct.

B, Sharply demarcated white infarct in the spleen.

Pulmonary infarctionPulmonary infarction

Splenic infarctionSplenic infarction

Histology of infarctionHistology of infarction

Changes depends on timeIschemic coagulative necrosisInflammationLiquifactive necrosisAbscess formationScar tissue

Remote kidney infarct, now replaced by a large

fibrotic cortical scar.

Factors That Influence Factors That Influence Development of an InfarctDevelopment of an Infarct

The major determinants include: (1) the nature of the vascular supply; (2) the rate of development of the occlusion; (3) the vulnerability of a given tissue to

hypoxia; and (4) the blood oxygen content.

Factors That Influence Factors That Influence Development of an InfarctDevelopment of an Infarct

The major determinants: (1) Nature of the vascular supply (double or single blood

supply) The availability of an alternative blood supply is the most important

factor in determining whether occlusion of a vessel will cause damage.

Lungs, for example, have a dual pulmonary and bronchial artery blood supply; thus, obstruction of a small pulmonary arteriole does not cause infarction in an otherwise healthy individual with an intact bronchial circulation.

Similarly, the liver, with its dual hepatic artery and portal vein circulation, and

the hand and forearm, with their dual radial and ulnar arterial supply, are all relatively insensitive to infarction.

In contrast, renal and splenic circulations are end-arterial, and obstruction of such vessels generally causes infarction.

Factors That Influence Factors That Influence Development of an InfarctDevelopment of an Infarct

The major determinants: (2) Rate of development of occlusion. Slowly developing occlusions are less likely to cause

infarction because they provide time for the development of alternative perfusion pathways. For example, small interarteriolar anastomoses —normally with minimal functional flow—interconnect the three major coronary arteries in the heart. If one of the coronaries is only slowly occluded (i.e., by an encroaching atherosclerotic plaque), flow within this collateral circulation may increase sufficiently to prevent infarction, even though the major coronary artery is eventually occluded.

Factors That Influence Factors That Influence Development of an InfarctDevelopment of an Infarct

The major determinants: (3) Vulnerability to hypoxia. The susceptibility of a tissue to hypoxia influences

the likelihood of infarction. Neurons undergo irreversible damage when

deprived of their blood supply for only 3 to 4 minutes.

Myocardial cells, although hardier than neurons, are also quite sensitive and die after only 20 to 30 minutes of ischemia.

In contrast, fibroblasts within myocardium remain viable even after many hours of ischemia

Factors That Influence Factors That Influence Development of an InfarctDevelopment of an Infarct

The major determinants: (4) Oxygen content of blood. The partial pressure of oxygen in blood also

determines the outcome of vascular occlusion. Partial flow obstruction of a small vessel in an

anemic or cyanotic patient might lead to tissue infarction, whereas it would be without effect under conditions of normal oxygen tension.

In this way, congestive heart failure, with compromised flow and ventilation, could cause infarction in the setting of an otherwise inconsequential blockage.

Factors That Influence Factors That Influence Development of an InfarctDevelopment of an Infarct

The major determinants: (4) Oxygen content of blood.

What is the critical value for HGB ?

Compartment syndrome

Compartment syndrome

Inguinal hernia

Inguinal hernia

Strangulated hernia

Umbilical hernia

Umbilical Hernia

Umbilical hernia

Volvulus

Volvulus

Volvulus involving caecum

Torsion - ovary

Torsion - ovary

Torsion - ovary

Torsion – Fallopian tube

Torsion testis – torsion of hydatid

Torsion - testis

Gangrene of Gangrene of the fingersthe fingers

E N DE N D