Infarct

Classification

1. Color (amount of hemorrhage)

2. Presence of infection

• Bland infarct - no infection
• Septic infarct - infected cardiac valve vegetations embolize to tissue, converting the infarct into an abscess

Gross Morphology

• Infarcts tend to be wedge-shaped, with the occluded vessel at the apex and the organ periphery at the base
• When the base is a serosal surface, a fibrinous exudate forms over it
• Acute infarcts have indistinct, slightly hemorrhagic margins; over time, edges become better defined by a rim of hyperemia from inflammation
• White infarcts become progressively paler and sharper with time
• Hemorrhagic infarcts leave a firm, brown residue as extravasated RBCs are phagocytosed and heme is converted to hemosiderin

Histology

• The main finding is ischemic coagulative necrosis
• Exception: the brain undergoes liquefactive necrosis
• Inflammatory response begins at the margins within a few hours, well defined by 1-2 days
• Inflammation is followed by repair - parenchymal regeneration at periphery (if stromal architecture is spared), or replacement by scar

Factors That Influence Infarct Development

1. Anatomy of the vascular supply

• Lung (pulmonary + bronchial arteries) - resistant, unless both are compromised
• Liver (hepatic artery + portal vein) - resistant
• Hand/forearm (radial + ulnar arteries) - resistant
• Kidney and spleen have end-arterial circulations - very susceptible

2. Rate of occlusion

• Slowly developing occlusions allow time for collateral vessel development - may prevent infarction even with complete occlusion (e.g., gradual coronary atherosclerosis allows interarteriolar anastomoses to enlarge)
• Sudden occlusion - no time for collaterals - infarction likely

3. Tissue vulnerability to hypoxia

Common Sites and Clinical Examples

Remote/Healed Infarct

• Ultimately replaced by fibrous scar
• Once completely healed, it is impossible to distinguish its age - an 8-week-old scar looks the same as a 10-year-old scar

Symptoms of Infarction (by site)

1. Myocardial Infarction (Heart)

• Chest discomfort - pressure, tightness, squeezing; may radiate to the upper extremity, jaw (mandibular), or epigastrium
• Diaphoresis (sweating)
• Nausea / vomiting
• Syncope
• Dyspnea (shortness of breath) - an "angina equivalent"
• Fatigue
• Symptoms typically last >20 minutes and may occur at rest
• Atypical presentations are common in women, diabetics, and postoperative patients - these groups may have only dyspnea or fatigue with no chest pain

2. Pulmonary Infarction (Lung)

• Dyspnea - the most common symptom (75-80% of patients); may be sudden or gradual
• Pleuritic chest pain - sharp, severe, worsens with deep breathing; present in ~20% of PE cases and typically indicates peripheral infarction
• Hemoptysis - coughing up blood (minority of cases)
• Cough
• Low-grade fever (temperature >38.6°C / 101.5°F suggests infection rather than infarction)
• Tachycardia - the most common vital sign abnormality
• Unilateral leg swelling (if underlying DVT is the source)
• Syncope (rare, <5%, but when unexplained should raise suspicion)
• Severe cases: cardiovascular collapse, cardiac arrest (pulseless electrical activity)

Note: Pulmonary infarction symptoms can resemble lobar pneumonia (pleuritic pain + cough + fever). Distinguishing features: PE fever is low-grade, and productive cough for days suggests pneumonia.

3. Cerebral Infarction (Stroke)

• Sudden hemiplegia or hemiparesis (one-sided weakness)
• Aphasia (speech difficulty)
• Facial droop
• Visual disturbances (hemianopia, diplopia)
• Dysarthria (slurred speech)
• Ataxia (loss of coordination)
• Sudden confusion or altered consciousness
• A "stroke in evolution" = progressive worsening of neurological signs

4. Renal Infarction (Kidney)

• Flank pain (sudden onset)
• Hematuria (blood in urine)
• Fever
• Nausea/vomiting
• May be asymptomatic if small

5. Splenic Infarction

• Left upper quadrant pain, often radiating to the left shoulder
• Fever
• May be asymptomatic (discovered incidentally)

6. Mesenteric (Intestinal) Infarction

• Severe, diffuse abdominal pain - "pain out of proportion to physical findings" is a classic warning sign
• Nausea / vomiting
• Bloody diarrhea
• Abdominal distension
• Signs of peritonitis (guarding, rigidity) if bowel necrosis/perforation occurs
• Can progress to septic shock

7. Testicular Infarction (Torsion)

• Sudden, severe scrotal pain
• Scrotal swelling and tenderness
• Nausea / vomiting
• Absent cremasteric reflex

Summary Table