Classification and Terminology
Bleeding is divided into external (blood pours into the external environment) and internal (blood accumulates in body cavities or the lumens of hollow organs).
Depending on the source, bleeding is classified as arterial, venous, arteriovenous, capillary, parenchymal, and cardiac.
Specialized terminology is used to describe blood accumulation in specific areas:
- Hemothorax — in the pleural cavity.
- Hemopericardium — in the pericardial cavity.
- Hemoperitoneum — in the peritoneal cavity.
- Hemarthrosis — in the joint cavity.
- Melena — intestinal bleeding.
- Metrorrhagia — uterine bleeding not associated with the normal menstrual cycle.
Types of Hemorrhages
A hemorrhage is a specific type of bleeding. Depending on the nature of tissue damage, several types are distinguished:
- Hematoma — accompanied by disruption of tissue integrity and the formation of a pathological cavity filled with clotted or liquid blood.
- Hemorrhagic imbibition (infiltration) — tissue structure is preserved; it is merely soaked with erythrocytes.
- Bruise (ecchymoma) — a flat accumulation of blood in the skin, subcutaneous tissue, or mucous membranes. If the diameter exceeds 2 cm, it is called an ecchymosis.
- Petechiae — small, pinpoint hemorrhages. Multiple petechiae that merge into larger foci form hemorrhagic purpura.
Mechanisms of Development
Blood escapes beyond the vessel wall via one of three main mechanisms:
- Rupture (haemorragia per rhexin). Occurs due to mechanical trauma, wall necrosis (e.g., myocardial rupture in myocardial infarction), inflammation (syphilitic mesaortitis), or aneurysm rupture.
- Erosion (haemorragia per diabrosin). Arrosion bleeding in which the entire thickness of the vascular wall is destroyed by a pathological process. Causes include purulent inflammation, malignant tumor breakdown, caseous necrosis (in the wall of a tuberculous cavity), chemical action (gastric juice in an ulcer), or chorionic villi invasion (in ectopic pregnancy).
- Diapedesis (haemorragia per diapedesin). Seepage of blood through intact microcirculatory vessels due to increased permeability. Observed in severe hypoxia, intoxications, systemic vasculitis, leukemias, uremia, and hypertensive crises.
Etiology and Hemorrhagic Diathesis
Hemorrhagic diathesis is a pathological tendency to spontaneous bleeding in response to minor trauma. The underlying causes include:
- Increased vascular fragility: congenital defects, hypovitaminosis, infections, and the consequences of steroid therapy.
- Platelet defects: decreased count (thrombocytopenia), impaired adhesion (von Willebrand disease, Bernard–Soulier syndrome), or weakened aggregation.
- Deficiency of coagulation factors: congenital (hemophilia A — factor VIII deficiency, hemophilia B — factor IX deficiency) or acquired (liver disease, vitamin K deficiency).
- Excessive intravascular coagulation: characteristic of DIC (disseminated intravascular coagulation).
Plasmorrhagia
Plasmorrhagia is the escape of blood plasma from the vessel lumen followed by the imbibition of surrounding tissues. This process is associated with damage to the vascular intima and altered blood properties.
Mechanisms of plasma exit (primarily transendothelial):
- Ultrafiltration through basement membrane pores during pressure spikes.
- Diffusion along a concentration gradient.
- Microvesicular transport (micropinocytosis).
- Interendothelial exit (rarely seen under normal conditions).
Under light microscopy, the microvessel wall appears thickened and homogeneous. Electron microscopy reveals endothelial cell swelling, the appearance of fenestrae, and loosening of the basement membrane. In mild cases, plasmorrhagia ends in hyalinosis of the vessel wall; in severe cases, it leads to fibrinoid necrosis.
Outcomes and Clinical Significance
The clinical significance of bleeding depends on its type, volume, duration, and, above all, localization.
- Acute bleeding: arterial bleeding threatens massive blood loss and death from acute anemia. Heart rupture leads to hemopericardium — even 100–200 mL of blood causes fatal tamponade.
- Chronic bleeding: prolonged loss of small volumes of blood (e.g., from a stomach ulcer) leads to chronic post-hemorrhagic anemia.
- Localization of hemorrhage: a massive subcutaneous bruise is not life-threatening, whereas even a tiny hemorrhage in the brain can cause edema and death.
Hemorrhage outcomes can be favorable (resorption, organization, encapsulation) or unfavorable (suppuration upon infection). In the brain, a "rusty" cyst often forms at the site of a hematoma, colored by the accumulation of the pigment hemosiderin.