A 58-year-old man from Delhi presents to the emergency department with acute onset dyspnea and pleuritic chest pain for 6 hours. He underwent total knee replacement 10 days ago. On examination, he is tachycardic (HR 112/min), tachypneic (RR 28/min), and hypoxic (SpO₂ 88% on room air). Blood pressure is 95/60 mmHg. Chest X-ray shows a wedge-shaped opacity in the right lower lobe. ECG shows sinus tachycardia with T-wave inversion in leads V1–V4. D-dimer is markedly elevated. CT pulmonary angiography (CTPA) confirms acute pulmonary embolism with right ventricular dilatation. Which of the following pathological findings would you expect on histological examination of the affected lung tissue?

Question

Accepted Answer

C. Hemorrhagic infarction with intact alveolar architecture. ## Pathological Basis of Pulmonary Infarction

### Mechanism of Lung Infarction in PE

**Key Point:** Pulmonary infarction occurs in only ~10% of pulmonary emboli because the lungs have a dual blood supply (pulmonary and bronchial arteries). Infarction develops when a distal pulmonary artery is occluded in the setting of compromised bronchial circulation (e.g., left heart failure, shock) or impaired venous drainage.

### Classic Histological Finding: Hemorrhagic Infarction with Preserved Architecture

**High-Yield (Robbins Pathology):** The hallmark of pulmonary infarction is **hemorrhagic infarction with preservation of the underlying alveolar architecture** — at least in the early/acute phase. Key microscopic features include:

| Feature | Description |
|---------|-------------|
| **Necrosis type** | Coagulative necrosis — cell outlines preserved, nuclei lost (ghost outlines) |
| **Hemorrhage** | Extensive intra-alveolar hemorrhage filling alveolar spaces |
| **Alveolar architecture** | **Intact/preserved** — the alveolar walls and septal framework remain recognizable |
| **Inflammatory response** | Minimal early; neutrophilic infiltration appears at the margins later |
| **Timing** | Hemorrhagic infarct visible within 24–48 h; organization begins day 5–7 |

This is why **Option A** — *hemorrhagic infarction with intact alveolar architecture* — is the correct answer. The lung, unlike solid organs, undergoes hemorrhagic (not pale) infarction, and the preserved alveolar scaffold is the key distinguishing histological feature.

### Why Option B Is Incorrect

Option B describes "coagulative necrosis with neutrophilic infiltration and fibrin deposition." While coagulative necrosis is indeed the underlying necrosis type, the **defining and distinguishing** histological hallmark of pulmonary infarction is the **hemorrhagic character with preserved alveolar architecture** — not neutrophilic infiltration (which is more characteristic of bacterial pneumonia/abscess) or prominent fibrin deposition (more characteristic of DAD/ARDS). Option B's description more closely resembles an organizing pneumonia or early abscess than a classic pulmonary infarct.

### Distinguishing Features from Other Lung Pathologies

| Condition | Key Histological Feature |
|-----------|--------------------------|
| **PE with infarction** | Hemorrhagic infarction, preserved alveolar outline, coagulative necrosis |
| **Bacterial pneumonia** | Purulent (neutrophilic) exudate, organisms, no preserved architecture |
| **Tuberculosis** | Caseous (cheese-like) necrosis, granulomas, Langhans giant cells, AFB |

**Clinical Pearl:** This patient's wedge-shaped opacity (Hampton's hump) on CXR, hemodynamic compromise, and RV dilatation on CTPA confirm massive PE with infarction. The dual blood supply of the lung means infarction is uncommon, but when it occurs (as here, with shock reducing bronchial perfusion), the result is a **hemorrhagic infarct with preserved alveolar architecture** — the classic Robbins teaching point.

**Mnemonic: HIPA** — **H**emorrhagic infarction, **I**ntact alveolar architecture, **P**ulmonary embolism, **A**cute coagulative necrosis.

Answer

A. Coagulative necrosis with neutrophilic infiltration and fibrin deposition

Answer

B. Acute bronchopneumonia with purulent exudate

Answer

D. Granulomatous inflammation with caseous necrosis

Explanation

Pathological Basis of Pulmonary Infarction

Mechanism of Lung Infarction in PE

Classic Histological Finding: Hemorrhagic Infarction with Preserved Architecture

Why Option B Is Incorrect

Distinguishing Features from Other Lung Pathologies

Practice similar questions

Join our NEET PG community

Feature	Description
Necrosis type	Coagulative necrosis — cell outlines preserved, nuclei lost (ghost outlines)
Hemorrhage	Extensive intra-alveolar hemorrhage filling alveolar spaces
Alveolar architecture	Intact/preserved — the alveolar walls and septal framework remain recognizable
Inflammatory response	Minimal early; neutrophilic infiltration appears at the margins later
Timing	Hemorrhagic infarct visible within 24–48 h; organization begins day 5–7

Condition	Key Histological Feature
PE with infarction	Hemorrhagic infarction, preserved alveolar outline, coagulative necrosis
Bacterial pneumonia	Purulent (neutrophilic) exudate, organisms, no preserved architecture
Tuberculosis	Caseous (cheese-like) necrosis, granulomas, Langhans giant cells, AFB