Venous Congestion

Generalised (Systemic) Venous Congestion

• Usually associated with increased in circulation time due to cardiac pumping inefficiency.
  • The cardiac inefficiency is usually the result of:
    1. Cardiac disease, e.g.
       • Valvular disease
       • Myocardial degeneration
       • Cardiac malformation
    2. Increased pulmonary vascular resistance
       • Due to fibrosis or emphysema.
  • Reduced cardiac output gives an increased circulation time and a larger venous volume.
  • The relative quantity of deoxygenated blood in tissues rises.
• Some organs are more susceptible to venous congestion than others.
  • Lungs
  • Liver
  • Spleen
  • Kidneys (to a lesser extent)).

Pathology

• Severe congestion results in increased size and weight of organs.
  • Ultimately, oedema occurs.
• Encapsulated organs (e.g. spleen, liver):
  • Become swollen.
    • Turgid on palpation.
    • Have rounded free borders.
  • Are frequently darker red or purple.
  • Ooze dark (deoxygenated) blood on cut surface.
• Oedema fluid may be seen (e.g. lung) if the condition is prolonged.
  • E.g. in the lung.
• Accumulation of deoxygenated blood often results in cyanosis of tissues.
• Where the condition persists, hypoxia induces degenerative changes and fibrosis.
  • Replacement of degenerate tissue by more compact fibrous tissue often leads to irregular surface depressions known as induration.
• Where changes are more insidious, cellular and organoid atrophy may occur with diminution in size.

Sequelae

• Severe congestion can induce:
  • Oedema formation
    • E.g. in the lung, associated with cardiac mitral valvular disease.
  • Stagnation hypoxia and capillary damage
  • Minor capillary haemorrhage is induced by hypoxia.
    • Is often followed by haemosiderin deposition.
  • Fatty change
    • Degenerative change, characterised by fatty change, occurs when whole parenchymatous organs are affected.
      • E.g. the liver and kidneys.

Localised Venous Congestion

• Affects individual organs or tissues.
• May be
  • Acute
    • E.g. due to sudden blockage of drainage.
  • More chronic.
    • A slower but progressive blockage to venous drainage.
    • May result in tissue atrophy.

Causes

1. Extra-vascular pressure, for example
   • Ligatures or bandages.
   • Adjacent masses
     • Tumours
     • Abscesses
     • Granulomas
   • Organ displacements or torsions.
2. Intra-vascular obstruction
   • Thrombosis or embolism.
3. Vasculitis
   • Inflammation in and around the vessel wall (phlebitis).
   • May be iatrogenic.

Gross

• The affected organs or tissues show similar changes to venous congestion of systemic origin.
  • Here, the changes are confined to one organ or tissue area.
• Organ displacements, e.g. intussusception, often show venous congestion followed by hypoxic degeneration and sloughing of tissue.

Histological

• Affected tissues are seen to be congested .
  • Red blood cell stasis in venules and capillaries.
• Degeneration of tissue cells in the area affected.
  • Varying numbers of inflammatory cells around these degenerate foci.
    • Oedema and leaked plasma protein deposits.

Sequelae

• Sequelae depend on:
  • Severity
  • Speed of onset of hypoxia
  • Presence of alternative routes of venous drainage.
• The usual effect is hypoxic localised degeneration.
• Insidious, long-standing congestion tends to result in a combination of fibrosis and atrophy.

Hypostatic Congestion

• Seen in long-term recumbent, chronically ill animals, or those dying slowly.
• The term refers to congestion of the dependant parts of an organ in a failing circulation.
  • In cases of paired organs, it applies to the dependant organ .
• Particularly affects the lungs and kidneys.