A 38-year-old woman presents with acute onset of severe chest pain and a pericardial friction rub. Histology shows fibrin deposition in the pericardium with neutrophilic infiltration. Which acute inflammatory pattern best explains these findings, and what is the key distinguishing feature from suppurative pericarditis?

Question

Accepted Answer

A. Fibrinous inflammation; absence of abscess or localized pus collection. ## Fibrinous vs. Suppurative Pericarditis

### Clinical Context

**Key Point:** The patient has **acute fibrinous pericarditis** (likely post-viral or post-MI), characterized by fibrin deposition and a **friction rub** on auscultation. The critical discriminator from suppurative (purulent) pericarditis is the **absence of pus formation and abscess**.

### Pathological Comparison

| Feature | Fibrinous Pericarditis | Suppurative Pericarditis |
|---------|------------------------|-------------------------|
| **Exudate type** | Fibrin-rich, serofibrinous | Purulent (pus) |
| **Cell infiltrate** | Neutrophils + fibrin | Neutrophils + bacteria |
| **Abscess formation** | No | Yes (localized pus pocket) |
| **Auscultatory finding** | Friction rub | May be absent if large effusion |
| **Etiology** | Viral, post-MI, autoimmune, rheumatic | Bacterial infection (S. aureus, Streptococcus, TB) |
| **Outcome** | Resolution or adhesions | Tamponade, constrictive pericarditis if untreated |
| **Treatment** | NSAIDs, corticosteroids | Antibiotics + drainage |

### Why Fibrinous, Not Suppurative?

**High-Yield:** Fibrinous inflammation = **fibrin deposition** in tissue and vessel walls. Suppurative inflammation = **pus formation** (dead neutrophils + bacteria + necrotic debris).

The **friction rub** is pathognomonic for fibrinous pericarditis — it results from rough, fibrin-coated pericardial surfaces rubbing together. Suppurative pericarditis typically presents with a large effusion that muffles heart sounds; friction rub is less prominent.

**Clinical Pearl:** Post-MI pericarditis (Dressler syndrome) is classically fibrinous, not suppurative. The immune response to cardiac necrosis triggers fibrin deposition, not bacterial infection.

### Discriminating Feature: Absence of Abscess

**Mnemonic:** **FIB** = **F**ibrin, **I**mmune-mediated, **B**enign course (usually). **PUS** = **P**yogenic bacteria, **U**ncontrolled, **S**evere (requires drainage).

Fibrinous inflammation does not form a localized pus collection (abscess). Suppurative inflammation, by definition, does. This is the single most important discriminator.

[cite:Robbins 10e Ch 2]

Answer

B. Hemorrhagic inflammation; red blood cell extravasation predominates

Answer

C. Serous inflammation; clear, protein-rich exudate without fibrin

Answer

D. Purulent inflammation; presence of organized granulation tissue

Explanation

Fibrinous vs. Suppurative Pericarditis

Clinical Context

Pathological Comparison

Why Fibrinous, Not Suppurative?

Discriminating Feature: Absence of Abscess

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Feature	Fibrinous Pericarditis	Suppurative Pericarditis
Exudate type	Fibrin-rich, serofibrinous	Purulent (pus)
Cell infiltrate	Neutrophils + fibrin	Neutrophils + bacteria
Abscess formation	No	Yes (localized pus pocket)
Auscultatory finding	Friction rub	May be absent if large effusion
Etiology	Viral, post-MI, autoimmune, rheumatic	Bacterial infection (S. aureus, Streptococcus, TB)
Outcome	Resolution or adhesions	Tamponade, constrictive pericarditis if untreated
Treatment	NSAIDs, corticosteroids	Antibiotics + drainage