[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Inflammation](https://durgical.com/en/general-pathology/#a-inflammation) › Patterns of acute inflammation: serous, fibrinous, purulent, abscess, ulcer [General pathology](https://durgical.com/en/general-pathology/) · [Inflammation](https://durgical.com/en/general-pathology/#a-inflammation) # Patterns of acute inflammation: serous, fibrinous, purulent, abscess, ulcer - Lesion Acute inflammation looks different depending on what leaks out: clear fluid, fibrin, pus or a gap in the surface. The pattern points to the cause. Updated 2026-11-01 ## Key points - Serous = thin fluid (blister); fibrinous = fibrin on serosa (pericarditis, rub); purulent = pus (neutrophils plus liquefied tissue). - Abscess = localised pus with a wall; it usually needs drainage. - Ulcer = loss of surface epithelium (peptic, aphthous, venous, pressure). - Fibrin that is not removed → organisation → adhesions or scar. - Pseudomembrane: Clostridioides difficile colitis and diphtheria. ## What it is The pattern of acute inflammation depends on how severe the injury is, where it happens and what causes it. Mild leakage gives serous fluid; larger leaks let fibrinogen out to form fibrin; pyogenic bacteria produce pus and abscesses; and loss of a surface lining leaves an ulcer. Pathologists read these patterns under the microscope, and clinicians see them as effusions, blisters, friction rubs and wounds. ## Key facts - Fibrin removed by fibrinolysis allows resolution; fibrin that persists is invaded by fibroblasts and vessels (organisation) and becomes scar. - Pyogenic (pus-forming) bacteria include staphylococci, streptococci, pneumococci, gram-negative rods and anaerobes. ## Structure - Serous: thin, protein-poor fluid in a body cavity or under the epidermis (blister); few cells. - Fibrinous: pink meshwork of fibrin on serosal surfaces; grossly a shaggy, ‘bread-and-butter’ look on the pericardium. - Purulent (suppurative): pus made of neutrophils, liquefied necrotic cells and oedema fluid; creamy yellow exudate. - Abscess: localised pus in a cavity; necrotic centre, rim of preserved neutrophils, then vessels and fibroblasts that wall it off. - Ulcer: local defect of an epithelial surface; an acute ulcer base has neutrophils and fibrin, a chronic one adds granulation tissue and scar. - Pseudomembranous: fibrin, neutrophils and necrotic epithelium forming an adherent membrane. ## Patterns, what leaks out and classic examples | Pattern | What leaks out or is lost | Classic examples | | --- | --- | --- | | Serous | Thin fluid from plasma or mesothelial cells | Burn or friction blister, viral blister, early pleural or pericardial effusion | | Fibrinous | Fibrinogen, which polymerises into fibrin | Fibrinous pericarditis (after infarction, uraemia), lobar pneumonia, meningitis | | Purulent | Neutrophils, liquefied tissue and fluid | Acute appendicitis, bacterial pneumonia, bacterial meningitis | | Abscess | Walled-off pus, often Staphylococcus aureus or mixed anaerobes | Furuncle, lung abscess after aspiration, liver abscess | | Ulcer | Surface epithelium | Peptic ulcer, aphthous ulcer, venous and pressure ulcers | | Pseudomembranous | Fibrin and necrotic epithelium forming a membrane | Clostridioides difficile colitis, diphtheria | ## Clinical notes - A pericardial friction rub is the sound of fibrinous pericarditis; if the fibrin organises it leaves adhesions and can lead to constrictive pericarditis. - Antibiotics penetrate the walled-off cavity of an abscess poorly, so drainage is the mainstay of treatment. - Pus inside a pre-existing body cavity is called empyema (pleura, gallbladder). ## Memory aid Water, glue, cream, cave, crater: serous, fibrinous, purulent, abscess, ulcer. ## Test yourself Think of the answer, then tap the question to see it. ## What causes the ‘bread-and-butter’ look of the pericardium after a myocardial infarction? Fibrinous pericarditis: fibrin strands laid down on both pericardial layers that are pulled apart. ## What is pus made of? Neutrophils (many of them dead), liquefied necrotic tissue, oedema fluid and often the causative bacteria. ## Why is drainage the key treatment for an abscess? The fibrous wall and necrotic centre limit blood supply and antibiotic penetration, so the pus must be evacuated. [Add to my cards (3)](https://durgical.app/estudiar/?add=/en/general-pathology/patterns-of-acute-inflammation-serous-fibrinous-purulent-abscess-ulcer/) ## Related - [Outcomes of acute inflammation: resolution, abscess, scar or chronic inflammation](https://durgical.com/en/general-pathology/outcomes-of-acute-inflammation-resolution-abscess-scar-or-chronic-inflammation/) - [Vascular changes in acute inflammation: vasodilation, leakage, exudate vs transudate](https://durgical.com/en/general-pathology/vascular-changes-in-acute-inflammation-vasodilation-leakage-exudate-vs-transudat/) - [Inflammation: the cardinal signs and its five steps](https://durgical.com/en/general-pathology/inflammation-the-cardinal-signs-and-its-five-steps/) - [Patterns of necrosis: coagulative, liquefactive, caseous, fat, fibrinoid, gangrenous](https://durgical.com/en/general-pathology/patterns-of-necrosis-coagulative-liquefactive-caseous-fat-fibrinoid-gangrenous/) - [Chronic inflammation: causes, cells and features](https://durgical.com/en/general-pathology/chronic-inflammation-causes-cells-and-features/) ## Related conditions - [Acute appendicitis](https://durgical.com/en/conditions/acute-appendicitis/) - [Community-acquired pneumonia](https://durgical.com/en/conditions/community-acquired-pneumonia/) - [Peptic ulcer disease](https://durgical.com/en/conditions/peptic-ulcer-disease/) - [Abscess, furuncle and carbuncle](https://durgical.com/en/conditions/abscess-furuncle-and-carbuncle/) - [Lung abscess](https://durgical.com/en/conditions/lung-abscess/) - [Acute pericarditis](https://durgical.com/en/conditions/acute-pericarditis/) - [Bacterial meningitis](https://durgical.com/en/conditions/bacterial-meningitis/) - [Clostridioides difficile infection](https://durgical.com/en/conditions/clostridioides-difficile-infection/) - [Diphtheria](https://durgical.com/en/conditions/diphtheria/) - [Parapneumonic effusion and empyema](https://durgical.com/en/conditions/parapneumonic-effusion-and-empyema/) - [Burns (thermal, chemical, electrical; inhalation injury)](https://durgical.com/en/conditions/burns/) - [Recurrent aphthous stomatitis](https://durgical.com/en/conditions/recurrent-aphthous-stomatitis/) - [Constrictive pericarditis](https://durgical.com/en/conditions/constrictive-pericarditis/) ## Elsewhere in DurgiPedia - [Neutrophil](https://durgical.com/en/immunology/neutrophil/) - [Microscopy and stains: H&E, PAS, trichrome, silver, immunohistochemistry](https://durgical.com/en/histology/microscopy-and-stains-h-y-e-pas-trichrome-silver-immunohistochemistry/) - [Skin: epidermis layers, dermis, hypodermis](https://durgical.com/en/histology/skin-epidermis-layers-dermis-hypodermis/) ## Microorganisms - [Staphylococcus aureus](https://durgical.com/en/microbiology/staphylococcus-aureus/) - [Streptococcus pneumoniae](https://durgical.com/en/microbiology/streptococcus-pneumoniae/) - [Clostridioides difficile](https://durgical.com/en/microbiology/clostridioides-difficile/) - [Corynebacterium diphtheriae](https://durgical.com/en/microbiology/corynebacterium-diphtheriae/) [← All of general pathology](https://durgical.com/en/general-pathology/) Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given. Sources: [Abscess: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/001353.htm) (MedlinePlus, US National Library of Medicine, 2026); [Appendicitis](https://www.ncbi.nlm.nih.gov/books/NBK493193/) (StatPearls (NCBI Bookshelf), 2024); [Peptic Ulcer Disease](https://www.ncbi.nlm.nih.gov/books/NBK534792/) (StatPearls (NCBI Bookshelf), 2024). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/general-pathology/patterns-of-acute-inflammation-serous-fibrinous-purulent-abscess-ulcer/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/patterns-of-acute-inflammation-serous-fibrinous-purulent-abscess-ulcer/