Pneumonia anatomical path, Cheat Sheet of Pathology

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PNEUMONIAS, LUNG

ABSCESS AND

ATELECTASIS

BY

DR CHRISTIAN. C OGBU

MBBS, FMCPath, FRCPath (UK)

OBJECTIVES

OBJECTIVES

• (^) At the end of this lecture the students should be able to classify pneumonias.
• (^) List the etiologies.
• (^) Discuss the various types

Community-Acquired Bacterial Pneumonias

• (^) Bacterial pneumonias often follow a viral upper- respiratory tract infection.
• (^) S. pneumoniae (pneumococcus) is the most common cause of community-acquired acute pneumonias.

Streptococcus pneumoniae

• (^) Pneumococcal infections occur with increased frequency in two clinical settings: (1) chronic diseases such as chronic heart failure, COPD, or diabetes, and (2) congenital or acquired defects in immune responses.
• (^) In addition, decreased or absent splenic function greatly increases the risk for overwhelming pneumococcal sepsis.

Moraxella catarrhalis

• (^) M. catarrhalis is a cause of bacterial pneumonia in older adults, particularly in those with cardiopulmonary disease, diabetes, or immunodeficiency.
• (^) It is the second most common bacterial cause of acute exacerbation of COPD.

Staphylococcus aureus

• (^) S. aureus is an important cause of secondary bacterial pneumonia in children and healthy adults after viral respiratory illnesses.
• (^) It is associated with a high incidence of complications such as lung abscess and empyema.

Morphology

• (^) Bacterial pneumonia has two patterns of anatomic distribution: lobular bronchopneumonia and lobar pneumonia.
• Patchy consolidation of the lung is the dominant characteristic of bronchopneumonia, while consolidation of a large portion of a lobe or of an entire lobe defines lobar pneumonia.

• (^) In lobar pneumonia, four stages of the inflammatory response have classically been described.
• (^) In the first stage of congestion, the lung is heavy, wet, and red. It is characterized by vascular engorgement, intraalveolar fluid with few neutrophils, and often numerous bacteria.
• The stage of red hepatization that follows is characterized by massive confluent exudation, as neutrophils, red cells, and fibrin fill the alveolar spaces.

Complications of pneumonia include (1) tissue destruction and necrosis, causing abscess formation (2) spread of infection to the pleural cavity, causing pleuritis and the intrapleural fibrinosuppurative reaction known as empyema (3) bacteremic dissemination to the heart valves, pericardium, brain, kidneys, spleen, or joints, variously causing abscesses, endocarditis, meningitis, or suppurative arthritis.

Clinical Features

• (^) The major symptoms of typical community acquired acute bacterial pneumonia are abrupt onset of high fever, shaking chills, and cough producing mucopurulent sputum.
• (^) Occasionally, patients have hemoptysis.

Morphology

• (^) The morphologic patterns in viral pneumonias are similar.
• (^) It may be patchy or it may involve whole lobes bilaterally or unilaterally.
• (^) Macroscopically, the affected areas are red-blue and congested.
• (^) On histologic examination, the inflammatory reaction is largely confined to the walls of the alveoli.
• (^) The septa are widened and edematous; they usually contain a mononuclear inflammatory infiltrate of lymphocytes, macrophages, and, occasionally, plasma cells.
• (^) In severe cases, diffuse alveolar damage with hyaline membranes may develop.

Clinical Features

• (^) The course of viral pneumonia is extremely varied.
• (^) It may masquerade as an upper respiratory tract infection or “chest cold” that goes undiagnosed or manifest as a fulminant, life-threatening infection.

MORPHOLOGY

• (^) The yeast forms are fairly distinctive, allowing each of these fungi to be identified in tissue sections:
• (^) H. capsulatum: Round to oval, small yeast forms measuring 2 to 5 mm in diameter.
• (^) C. immitis: Thick-walled, nonbudding spherules, 20 to 60 mm in diameter, often filled with small endospores.
• B. dermatitidis: Round to oval yeast forms (5 to 25 mm in diameter) that reproduce by characteristic broad-based budding.

Clinical Features

• (^) The clinical symptoms and signs resemble those of a “flulike” syndrome and are most often self-limited.
• (^) In the vulnerable host, chronic cavitary pulmonary disease develops, with a predilection for the upper lobe, resembling the secondary form of tuberculosis.
• (^) Manifestations may include cough, hemoptysis, dyspnea, and chest pain.
• (^) Disseminated disease produces a febrile illness marked by hepatosplenomegaly, anemia, leukopenia, and thrombocytopenia.