Respiratory System

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Respiratory System

Five major disease categories are presented in this chapter: obstructive and restrictive disorders of gas exchange, vascular diseases of the lung, infectious and inflammatory diseases, and tumors of lungs and pleura.

Obstructive Lung Diseases

Chronic obstructive pulmonary disease (COPD) is characterized by a reduction of pulmonary air flow as determined by spirometric function tests with normal or increased total lung capacity (TLC) and forced vital capacity (FVC) in combination with decreased forced expiratory volume (FEV). COPD follows either increased resistance to airflow (e.g., by luminal narrowing of air ducts) or the loss of elastic recoil (by passive widening of air spaces). It can be caused by a number of different respiratory diseases, including chronic bronchitis, bronchiolitis and asthma, cystic fibrosis (CF), bronchiectasis, or α1-antitrypsin deficiency. COPD may lead to progressive and destructive emphysema and, eventually, cor pulmonale, characterized by reduced intrapulmonary blood flow, pulmonary hypertension, and right heart insufficiency.

Restrictive Lung Diseases

In restrictive lung diseases (RLDs), the lungs have a limited potential to expand, and therefore, compliance is reduced. Although extrapulmonary disorders such as chest abnormalities, intraabdominal masses, and neuromuscular diseases also can limit lung expansion, the term RLD is generally reserved for intrapulmonary parenchymatous diseases. In these cases, spirometric tests show a reduced FVC with normal or proportionately reduced FEV. RLD occurs in acute and chronic forms. Classic examples of acute RLD are the adult respiratory distress syndrome (ARDS) and acute hypersensitivity pneumonitis. Chronic forms include such pathogenetically different entities as idiopathic pulmonary fibroses (fibrosing alveolitis), chronic interstitial pneumonitis in collagen-vascular diseases, pneumoconioses, and sarcoidosis. Only patients in early stages of acute RLD may recover completely; later stages and especially the chronic forms of RLD remit to scarring or progress to extensive interstitial pulmonary fibrosis with honeycombing, pulmonary hypertension, and development of cor pulmonale. Recurrent superimposed infections further complicate the course of RLD.

Tumors in the Lungs and the Pleura

As in other organs, tumors of the lung are identified as carcinomas (e.g., of bronchial epithelium, bronchial glands, or alveolar lining cells) or as sarcomas. They are classified according to their cell of origin (squamous cell carcinoma [SCC], adenocarcinoma [AC], small-cell carcinoma [oat cell carcinoma]) and to their degree of differentiation. Their local extension and metastatic spread determine their prognosis. Consequently, both tumor classification and documentation of its spread (grading and staging) are important responsibilities of diagnostic pathology and form the basis for determining therapeutic intervention. In addition, the lungs are frequent sites of metastases from other locations (e.g., breast, pancreas, testes, bone, malignant melanoma of the skin, and others), which must be distinguished from primary lung tumors.

TABLE 3-1

CONDITIONS THAT CAN CAUSE ARDS/DAD*

Conditions Causes
Infectious diseases Septicemia with DAD and DIC (especially gram negative), diffuse pneumonitis by virus, mycoplasma, pneumocystis, tuberculosis (certain forms, e.g., typhobacillosis Landouzy)
Chemical injury and inhalants Oxygen, irritant gases and inhaled chemicals, barbiturate overdose, salicylic acid, paraquat, heroin or methadone overdose, cytotoxic drugs, uremic pneumonitis, gastric aspiration
Physical injury Trauma to lungs (contusion), head injury, fat embolism of various causes, air embolism, burns, ionizing radiation
Other Shock of any cause, acute pancreatitis, near drowning aspiration

*ARDS indicates adult respiratory distress syndrome; DAD, diffuse alveolar damage; DIC, disseminated intravascular coagulation.

TABLE 3-2

CLASSIFICATION OF IDIOPATHIC PULMONARY FIBROSIS*

Feature NSIP UIP DIP AIP LIP COP
Interstitial inflammation Prominent Scant Scant Scant Prominent Scant
Interstitial fibrosis            
Collagen Variable, diffuse Patchy Variable, diffuse No Some areas No
Fibroblast foci Occasional No No Yes, diffuse No No
BOOP Occasional, focal Occasional, focal No Occasional, focal No Prominent
Intraalveolar macrophages Occasional, patchy Occasional, patchy Yes, diffuse No Patchy No
Hyaline membranes No No No Yes, focal No No
Honeycombing Rare Yes No No Sometimes No

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*AIP indicates acute interstitial pneumonitis; BOOP, bronchiolitis obliterans organizing pneumonitis; DIP, desquamative interstitial pneumonitis; NSIP, nonspecific interstitial pneumonitis; UIP, usual interstitial pneumonitis, LIP lymphocytic interstitial pneumonitis, COP cryptogenic organizing pneumonitis.

From Leslie KO, Wick MR. Practical Pulmonary Pathology. Philadelphia, 2005, Churchill Livingstone.

TABLE 3-3

CLINICAL AND PATHOLOGIC FEATURES OF PNEUMOCONIOSES*

Entity Clinical Appearance Pathologic Changes
Coal miner’s lung Black lung disease Diffusely distributed, small focal anthracosilicosis, initially centriacinar and peribronchiolar with many carbon-laden macrophages and perifocal emphysema; extent of fibrosis depends on admixture of quartz
Silicosis Acute silicosis (uncommon) Alveolar lipoproteinosis and progressive diffuse interstitial fibrosis secondary to inhalation of small particulate silica crystals (e.g., after sand blasting)
  Nodular silicosis (common) Multiple growing silicotic nodules, usually 2 mm to 1 cm in diameter: fibrosing granulomas with concentric fibrous layering, some anthracotic pigment, small slitlike spaces, and needle-shaped crystalline spicules on polarization; perifocal emphysema
  Progressive massive silicosis Multiple silicotic granulomas up to 10 cm in diameter, both lungs involved, massive and rapidly progressive fibrosis
Asbestosis and asbestosrelated diseases Asbestosis per se Alveolitis with progressive interstitial fibrosis, deposition of asbestos bodies (golden-brown beaded rods consisting of asbestos fibers coated by ferroproteinaceous material); final stage: honeycombing lung
  Pleural plaques and rounded atelectasis Recurrent pleural fibrinous effusions, pleural fibrosis and pleural plaques (“sugar coating”), focal atelectasis secondary to pleural fibrosis
  Neoplasms Malignant mesothelioma (↑ risk of bronchogenic carcinoma)
Berylliosis Berylliosis per se Acute and recurrent pneumonitis, systemic sarcoidlike and fibrosing granulomas
Talcosis Talcosis per se Foreign body granulomas with birefringent talcum deposits, micronodular and diffuse interstitial fibrosis

*Caplan syndrome occurs in patients with rheumatoid arthritis and some form of nodular silicosis. Deposition of microparticulate iron causes siderotic macrophage response with secondary focal or diffuse interstitial fibrosis.

TABLE 3-4

INFECTIOUS AGENTS CAUSING PNEUMONIA

Class Etiologic Agent Type of Pneumonia
Bacteria Streptococcus pneumoniae  
Streptococcus pyogenes  
Staphylococcus aureus  
Klebsiella pneumoniae  
Pseudomonas aeruginosa  
Escherichia coli  
Yersinia pestis  
Legionella pneumophila Legionnaires disease
Peptostreptococcus, Peptococcus Aspiration (anaerobic) pneumonia
Bacteroides  
Fusobacterium  
Veillonella Bacterial pneumonias
Actinomycetes Actinomyces israelii Pulmonary nocardiosis
Nocardia asteroides Pulmonary actinomycosis
Fungi Coccidioides immitis Coccidioidomycosis
Histoplasma capsulatum Histoplasmosis
Blastomyces dermatitidis Blastomycosis
Aspergillus Aspergillosis
Phycomycetes Mucormycosis
Rickettsia Coxiella burnetii Q fever
Chlamydia Chlamydia psittaci Psittacosis
  Ornithosis
Mycoplasma Mycoplasma pneumoniae Mycoplasmal pneumonia
Viruses Influenza virus, adenovirus, respiratory syncytial virus, etc. Viral pneumonia
Protozoa Pneumocystis carinii Pneumocystis pneumonia (plasma cell  pneumonia)
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