Hyperemia is an active process: There is increased blood inflow caused by arteriolar dilation. (Example: skeletal muscle during exercise or at sites of inflammation).

Tissues are redder due to engorgement with oxygenated blood.

Normally, a fraction of the capillaries of an organ or tissue functions, others remain closed. When capillaries are injured (toxic or anoxic) or when more blood is required due to functional over activity, all the capillaries open up resulting in more blood in the part.

In chronic cases the capillary may rupture. This may cause focal hemorrhage and breakdown of erythrocytes at these sites. Hemosiderin-laden macrophages are often present.

Parenchymal cell atrophy or death may cause scarring.

Gross features: The involved organs appear brown with contraction and fibrosis - Example: Lungs ; Liver.

Congestion is a passive process: It is caused by impaired outflow from a tissue.

Isolated venous obstruction may cause local congestion.

Systemic venous obstruction occurs in congestive heart failure.

Tissues acquire a blue-red color (cyanosis) due to accumulation of deoxygenated hemoglobin.

Long-standing stasis may result in cell death. (Visit: CONGESTIVE HEART FAILURE )

Causes: (Visit: Cardiac Path Online ; Pulmonary Pathology Online )

a) Heart: Mitral valve disease (Example: stenosis/incompetence). Congenital heart disease (e.g. pulmonary stenosis, tricuspid regurgitation) and Myocardial infarct ; Cardiomyopathy.

(Visit: congenital heart disease ; CARDIOMYOPATHY ; Myocardial infarction )

b) Lung: Emphysema ; Pulmonary fibrosis. It causes reduction of pulmonary circulatory bed producing right heart failure leading to passive venous congestion.

Morphology:

Heart: In mitral stenosis heart shows hypertrophy and dilation of left atrium with formation of ball thrombus.

Lungs:

Gross features:

Grossly, lung is voluminous with impression of ribs, pits on pressure, dark brown in color, and feels firm.

Microscopic features:

Microscopically, alveoli contain edema fluid with intra alveolar hemorrhage (cause of hemoptysis) and "Heart failure cells" (hemosiderin filled macrophages).

Histopathology Image of Heart Failure Cells: click here

(Hemolysis of alveolar RBC liberates hemosiderin and bilirubin. Alveolar phagocytes engulf hemosiderin and carry them throughout the framework of lung, which stimulates fibrosis producing brown induration of lung and bilirubin cause latent jaundice).

Liver:

Gross features:

Liver is enlarged and soft. Cut surface shows alternate dark and pale areas ("Nutmeg liver") - dark area represent congested centrilobular zone and pale areas represent fatty middle zone and normal periportal areas. Macroscopic image of Nutmeg Liver: click here

Microscopic features: Histopathology Image of Liver showing Nutmeg Pattern due to Congestion around the Central Veins: click here

1. In centrilobular zone central vein and sinusoids are distended with blood and liver cells show necrosis (due to anoxia and pressure).

2. Mid zone shows fatty change.

3. Periportal zone is relatively normal (better oxygenated due to their proximity to hepatic arterioles.

In long-standing cases central vein is thickened with extension of fibrous tissue in to the surrounding lobules

Persistent hypoxia prevents regeneration of liver cells hence called cardiac sclerosis instead of cardiac cirrhosis.