Morphology of Inflammation

Inflammatory Lesions

Occurs in diverse tissues in response to diverse causal agents

Both the causal agent and the tissue contribute to the visible evidence of inflammation, the inflammatory lesion

The inflammatory lesion can aid the pathologist to accurately diagnose the cause of a disease

Examples: Serous Inflammation, Fibrinous Inflammation, Suppurative Inflammation, Ulcers, Granulation Tissue, Granulomas

Serous Inflammation

Outpouring of low MW (i.e. protein-poor) plasma components thru "leaky" minimally inflamed vessels

Edema: Protein-poor fluid accumulates in tissue interstitium; Grossly leads to swelling; Total body edema = anasarca

Serous Effusion: Protein-poor fluid accumulates in potential space (pleura, pericardium, peritoneum); May affect function of organs it displaces; called serous ascites in the peritoneum

Vesicle (Blister): Protein-poor fluid accumulates in a cleft beneath or within epithelium

Fibrinous Inflammation

Outpouring of all soluble (i.e. protein-rich) plasma components thru permeable more severely inflamed vessels

Fibrinous Exudate: Extravasated soluble fibrinogen (high MW plasma protein) is cleaved to form insoluble fibrin, which coats all available surfaces

Fibrinous Adhesion: Adjacent structures become stuck together by a loose fibrin matrix

Two possible outcomes of fibrinous inflammation: (1) Resolution : fibrin is reabsorbed and the tissue is restored to its original architecture. (2) Organization : fibrin is reabsorbed and a collagen scar is laid down

Suppurative Inflammation

Outpouring of neutrophil leukocytes and plasma proteins through the most inflamed vessels

(Fibrino-) Purulent Exudate: Extravasated fibrin matrix, neutrophils, and necrotic debris cling to available surfaces; Commonly known as pus

Abscess: Fibrinopurulent exudate localized in a walled-off focus with a necrotic center; If persistent, will eventually drain by communication with the skin through a sinus tract

Cellulitis: Poorly localized fibrinopurulent exudate in connective tissue; Characteristic of rapidly progressive infections

Granulation Tissue

Fibrin deposits that remain moist and retain contact with vascular supply undergo fibrovascular organization

Endothelial cells and fibroblasts grow into the fibrin matrix and gradually replace soft fibrin with a tough collagen scar

Fibrin/collagen matrix with ingrowth of new capillary branches, fibroblasts, and inflam. cells is called granulation tissue

Example: skinned knee Þ soft yellow scab that bleeds easily when you remove the bandage

Ulcers

Superficial inflammatory lesion caused by damage of surface epithelium

Fibrinous exudate in the base of an ulcer allows formation of granulation tissue

Ulcers can perforate hollow viscera, or penetrate from a surface into a solid organ

Granulomas

Chronic inflammatory lesions containing Epithelioid histiocytes(macrophages), Giant cells, Lymphocytes

Typical response of the body to stimuli that are difficult to degrade

Do not confuse "granuloma" with "granulation tissue"

Etiologies: Beryllium, Tuberculosis, Parasites, Foreign Bodies, Fungi, Sarcoid

Three morphologic types:

(1) Caseating granuloma

Contain a central core of granular eosinophilic necrotic material, grossly resembling goat cheese
Highly suggestive of, but not diagnostic for TB

(2) Non-caseating (Hard) granuloma

Central caseating necrosis is conspicuously absent
Typical of sarcoidosis if all other causes of granuloma can be excluded

(3) Suppurating granuloma

Characterized by a central abscess containing neutrophils
In appropriate setting, highly suggestive of "Cat scratch disease" caused by Bartonella (Rochalimaea) henseli