Suppurative Inflammation: Abscess Formation

• Suppurative inflammation is associated with pus formation
• Staphylococcus aureus and streptococcus haemolyticus are strong pyrogenic bacteria that can cause severe suppuration

Mechanism of Suppuration

• Strong pyogenic bacteria cause marked necrosis
• Neutrophils are attracted in large numbers, but die due to the bacteria's virulence
• Proteolytic enzymes, mainly from dead neutrophils, liquefy necrotic tissue and fibrin
• Liquefied material combines with pus cells and fluid exudate to form pus

Abscess

• Localized suppurative inflammation leads to an irregular pus-containing cavity formation
• Common sites include subcutaneous tissues or deep organs
• Early abscesses show a central necrotic zone and a surrounding zone of acute inflammation with neutrophils, developing into three zones
• Central necrotic core is surrounded by infected tissue
• An abscess cavity is formed in approximately 48 hours
• Peripheral zone of inflamed tissue is called the pyogenic membrane

Course and Fate of an Abscess

• Small abscesses may be absorbed and heal
• Large abscesses are slowly absorbed due to high osmotic pressure, which absorbs water, leading to increased size and throbbing pain
• Untreated abscesses may point, rupture, or spontaneously evacuate, potentially forming an ulcer

Complications of an Abscess

• Spontaneous evacuation can lead to non-healing and less repair
• Healing can result in much repair
• Chronic abscesses, if not evacuated, become surrounded by fibrosis, with pus drying and potential cholesterol crystal and dystrophic calcification

Spread of Infection

• Direct spread of infection can occur from a abscess
• Infections can spread via the lymphatic system
• Infections can also spread through the blood

Furuncle (Boil)

• Small abscesses relate to the hair follicle, sebaceous or sweat gland
• Staphylococci bacteria can cause furuncles
• Commonly found on hairy areas such as the face and armpits
• Multiple neighboring boils are called furunculosis

Carbuncle

• Acute localized suppurative inflammation that forms multiple communicating suppurative foci in the skin and subcutaneous fat which discharge pus through several openings
• Carbuncles are commonly caused by staphylococci and are common in individuals with diabetes
• Common sites are areas where the skin and subcutaneous tissue are thick and tough, such as the back of the neck, scalp, and buttocks

Cellulitis

• Acute diffuse suppurative inflammation
• Streptococci release fibrinolysin (streptokinase) and hyaluronidase, which dissolve fibrin and help spread infection
• Can occur in loose connective tissue, such as the orbit, scrotum & wall of the appendix
• Pus from streptococcal infections is thin, bloody, and contains necrotic debris

Complications of Cellulitis

• Lymphatic spread leads to acute lymphangitis and lymphadenitis
• Blood spread leads to septicemia and pyemia

Serous Inflammation

• Acute non-inflammation characterized by excess watery fluid exudate
• There is little to no fibrin present
• Skin blisters after a burn, and skin vesicles due to viral infections are examples

Serofibrinous Inflammation

• Characterized by excess fluid exudate rich in fibrin
• Such inflammation is often found in serous membranes like the pleura, peritoneum, and pericardium

Allergic Inflammation

• Characterized by fluid exudate rich in eosinophils
• Associated with hypersensitivity reactions like urticaria, bronchial asthma, allergic rhinitis, and contact dermatitis

Catarrhal Inflammation

• Mild acute non-suppurative inflammation that occurs on mucous membranes
• Characterized by excess mucous secretion

Pseudomembranous Inflammation

• Acute inflammation characterized by formation of a pseudomembrane
• Consists of fibrin, desquamated epithelium, and inflammatory cells
• Diphtheria and bacillary dysentery caused by Shigella bacilli can cause this
• Toxemia is a common complication, along with suffocation

Hemorrhagic Inflammation

• Acute inflammation characterized by vascular damage and hemorrhage in the exudate
• Often seen in meningococcal infections

Necrotizing Inflammation

• Acute non-suppurative inflammation is characterized by extensive tissue necrosis
• Can be seen in the oral mucosa of debilitated, malnourished children

Chronic Inflammation

• Characterized by lymphocytes, plasma cells, macrophages, and giant cells
• Often accompanied by fibrosis and endarteritis obliterans (EAO)

Microscopic Features of Chronic Inflammation

• Infiltration with mononuclear cells occurs
• Thick-walled blood vessels are present
• Fibrosis is common

Types of Chronic Inflammation

• Chronic non-specific inflammation follows acute inflammation, where many irritants produce the same lesion
• Chronic specific inflammation produces a specific lesion, and the irritant can be detected within the lesion