Page 383 - Concise Pathology for Exam Preparation ( PDFDrive )

368 SECTION II Diseases of Organ Systems

Microscopy

• Inflammation is restricted to the alveolar walls; alveolar space is free from exudate (thus
called atypical pneumonia). In contrast, in bacterial pneumonia the exudate is typically
intra-alveolar.
• The inflammatory infiltrate is composed of lymphocytes, histiocytes and plasma cells.
• Intra-alveolar spaces show proteinaceous material and the alveolar septal walls are lined
by pink hyaline membrane.
• Superimposed bacterial infections may lead to a picture-like bacterial pneumonia.
• In cytomegalovirus infection, giant cells with intranuclear or intracytoplasmic inclu-
sions may be seen.

Q. Outline the aetiopathogenesis, morphology and complications of
lung abscess.

Ans. Lung abscess is a localized suppurative process within the lungs which induces
necrosis of lung tissue.

Aetiopathogenesis
Causative Organisms
• Aerobic and anaerobic streptococci
• Staphylococcus aureus
• Bacteroides
• Fusobacterium
Predisposing Factors
• Oropharyngeal: Surgical procedures, dental sepsis and sinusitis
• Bronchial obstruction: Secretions, bronchiectasis and bronchogenic carcinoma
• Direct trauma, infection from other organs (direct and haematogenous spread)
• Aspiration of infective material: Gastric contents may be aspirated in comatose patients,
alcoholics, patients under anaesthesia, or with sinusitis and depressed cough reflex
• Antecedent primary bacterial infection particularly in immunosuppressed patients
(Staphylococcus aureus, Klebsiella pneumoniae, Streptococcus pyogenes and Pseudomonas)
• Septic embolism: From thrombophlebitis (affecting systemic veins) or infective bacterial
endocarditis vegetations in right side of the heart
• Idiopathic/primary cryptogenic lung abscess: No definite cause is found.
Morphology

• Characterized by suppurative destruction of the lung parenchyma with a central area of
cavitation
• May be solitary or multiple
• Pulmonary abscesses due to aspiration are more common on the right side due to the
more vertical right main bronchus; abscesses that develop secondary to pneumonias
and bronchiectasis are usually multiple, basal and diffusely scattered
• Abscesses due to septic emboli and pyemia are also multiple but may affect any region
of the lungs
• Superimposed saprophytic infections lead to a large, ill-defined, foul-smelling and
multilocular cavity (gangrene of the lung).

Complications
• Involvement of pleural cavity by extension of the infection (empyema)
• Haemorrhage

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