Infections In the Lung Flashcards
What are the clinical features of pneumonia?
- fever and chills
- unrelenting cough
- sputum production (purulent/yellow)
- chest pain (if pleura inflamed)
- impaired gas exchange resulting in SOB/dyspnoea and tachypnoea, and hypoxemia
Hospital patients are more susceptible to what type of pneumonia-causing agents?
gram negative bacteria (e.g. pseudomonas)
Immunocompromised hosts are more likely to get pneumonia caused by
fungi and protozoa (e.g pneumocystis jirovecii)
What are the 4 routes of infectious pathogens into the lungs?
- inhalation of pathogens in air droplets
- aspiration of infected secretions from URT
- aspiration of infected particles
- gastric contents, food, drink, foreign bodies
- haematogenous spread (via blood)
What are the 3 main causes of pneumonia?
- URT flora
- S. pneumoniae, H. influenzae, S. aureus
- enteric saprophytes, by contaminaiting airways or blood stream
- E. coli, Pseudomonas
- extraneous pathogens
- Legionella pneumophilia, TB
What are the 2 patterns of infective pneumonia?
- alveolar inflammation
- neutrophils in the alveolar spaces = consolidation
- Strep, Staph Haemophilus, G-ves
- neutrophils in the alveolar spaces = consolidation
- interstitial inflammation
- lymphocytes, macrophages, sometimes plasma cells in the connective tissue septa between the alveoli (interstitium)
- viruses, atypical pneumonia viruses (mycoplasma pneumoniae)
- lymphocytes, macrophages, sometimes plasma cells in the connective tissue septa between the alveoli (interstitium)
What are the two types of alveolar pneumonia?
- bronchopneumonia
- consolidation is patchy, multi-focal; very often bilateral (more than 1 lobe)
- lobar pneumonia
- involves an entire lobe and often inflammation of the adjacent pleura
What is the most common cause of lobar pneumonia?
S. pneumoniae (90%)
and H. influenzae
How is lobar pneumonia acquired?
- community acquired in adults 20-50
- commonly following viral URTI
What is the clinical presentation of lobar pneumonia?
- abrupt onset
- fever & chills
- rasied WBC
- cough
- pleuritic chest pain
- haemoptisis
- G+ diplococci in sputum
- bacteraemia
What are the 4 stages of lobar pneumonia?
- congestion of alveolar capillaries
- alveolar spaces filled with proteinaceous exudate containing G+ diplococci (Strep)
- red hepatization (consolidation)
- haemorrhage into air spaces
- grey hepatization
- fibrin, neutrophils, macrophages in alveolar spaces
- resolution
What is a cute bronchopneumonia?
- most common pattern of bacterial pneumonia
- patchy consolidation, often multi-focal and involving more than one lobe or lung
- centered on bronchioles, spreads into surrounding alveolar spaces
Acute bronchopneumonia is common in
- extremes of life
- secondary to pre-existing chronic disease
- COPD, congestive heart failure, malignancy, CF
- v. in hospitalized patients (G- bacteria & staph important causes)
- post-op complications that impair clearance of respiratory secretions
- secondary infection following viral UTI
Histologically, acute bronchopneumonia presents with
bronchioles and alveoli filled with neutrophils
What are the complications of pneumonia?
- pleuritis
- pyothorax (pus in pleural space)
- if becomes walled off by fibrous tissue = empyema
- abscesses
- cavities contaning pus (purulent exudate)
- commonly caused by staph aureus pneumonia, Klebsiella, or Pseudomonas
- chronic complications like bronchiectasis
What is the histologic presentation of interstitial pneumonia?
- may be oedema fluid, red cells, and fibrin in alvelolar spaces
- there are no alveolar neutrophils or inflammatory cells tf no consolidation
- macroscopically the lung appears wet, dark, and heavy
How does atypical pneumonia present on CXR?
- no consolidation pattern
- widespread changes throughout both lung fields
- reticulonodular infiltrate (dots and dashes)
What is primary TB?
- typically in childgood
- pathology is characterised by a Ghon’s complex
- area of inflammation (peripheral mid-zone of lung) called a Ghon focus
- mediastinal or hilar lymphnodes = granulomatous lymphadenopathy
- Ghon focus + enlarged lymph nodes = Ghon’s complex
- granuloma consists of:
- multinucleated giant cells
- epitheliod macrophages
- lymphocytes
- central caseuous (cheesy) necrosis
- usually asymptomatic
- heals, often involving calcification
- remains dormant until secondary infection arises
tuberculous granuloma
What are epitheliod macrophages?
- large, rounded pink cells
- form aggregates
What is the large arrow pointing to? The small arrow?
- large: caseous necrosis
- small: multinucleated macrophages/giant cells
What causes the formation of granulomas in TB?
- cell-mediated immune reaction type IV hypersensitivity
- monocytes exit peripheral blood in the area of the infection
- enter the tissue
- stimulated by cytokines (IFNy) to become epitheloid macrophages
- this forms a lump
What is the pattern of miliary TB?
- numerous small granulomas (~2-3mm) in lung and other organs
What is single-organ TB?
- usually caused by secondary TB with caseation
- other organs can be seeded with TB from primary infection
- seen in spine (Potts disease) and urogenital tract
- in kidney, see butterfly-shaped lesions of caseous necrosis in upper pole
- some cavitation occurs due to caseous material entering the collecting system
