Learning Objectives
Identify the pathophysiological differences between Red (Hemorrhagic) and Pale (Anemic) infarcts. Understand how tissue architecture and vascular supply dictate the morphological appearance of necrotic tissue following ischemia or venous occlusion.
1. Red (Hemorrhagic) Infarcts
Red infarcts occur when blood continues to enter an area of necrosis or leaks into the loose tissue after the initial insult. This typically happens in venous occlusions (where blood can enter but not leave) or in tissues with dual blood supplies.
| Mechanism | Context | Key Examples |
|---|---|---|
| Venous Occlusion | Blood enters via arteries but cannot exit, causing backup and hemorrhage. | Testicular torsion, Bowel volvulus. |
| Dual Supply | A secondary arterial system bleeds into the necrotic area. | Lung (Bronchial/Pulmonary), Liver (Hepatic art/Portal vein). |
| Reperfusion | Restoration of flow to damaged vessels (e.g., after angioplasty). | Post-thrombolytic therapy in MI or Stroke. |
Activity:
2. Pale (Anemic) Infarcts
Pale infarcts occur in solid organs with end-arterial circulation (a single blood supply). Because the tissue is dense, it limits the amount of blood that can seep into the necrotic area from adjacent capillary beds.
| Feature | Description | Classic Organs |
|---|---|---|
| Vascular Supply | Single “end-artery” with no significant collateral flow. | Heart (Coronaries). |
| Tissue Density | Solid, compact parenchyma prevents collateral bleeding. | Kidney, Spleen. |
| Appearance | Wedge-shaped, pale/tan color (apex points to occlusion). | Renal infarct. |
Activity:
High-Yield Mnemonics & Tips:
- Red vs. Pale: Think “Loose or Lush” for Red infarcts (Loose tissue like lungs, or Lush/dual supply like liver). Think “Solid and Single” for Pale infarcts (Solid organs, Single supply).
- Reperfusion Injury: Re-opening a vessel is generally good, but the sudden oxygen influx can create Free Radicals, turning a pale infarct into a hemorrhagic one.
- Wedge Shape: On imaging or gross pathology, infarcts in the kidney and spleen are characteristically wedge-shaped.