Pathology of Pneumonia Flashcards
What is acute pneumonia?
- Inflammatory reaction of the alveoli and interstitium of the lung usually caused by an infectious agent
Characterised by - inflammatory exudate (fluid made up of blood proteins etc that leak out) in the alveolar space that consolodiates (replacement and solidification of alveoli space)
- Inflammation of alveolar septa
- Leading cause of death from an infectious disease
What is the histology of acute pneumonia?
- Normal histology would consist of :
- Terminal and respiratory bronchioles
- Respiratory ducts
In pneumonia:
First few days - neutrophils and fluid in alveoli, congested capillaries (Red Hepatization)
- congestion makes walls look significantly bigger
- Fluid leaks and fills alveolar space from blood
-After 2-3 days : - Organisation exudates transformed to masses;
- macrophages and fibroblasts (Grey Hepatization)
- pale in colour
What is the aetiology of acute pneumonia?
- Bacteria:
- Gram +ve : Streptococcus pneumoniae, Staphylococcus aureus
- Gram -ve : Haemophilius influenzar, Klebsiella pneumoniae, Legionella pneumophila
- Viruses e,g, influenza A, RSV, SARS-CoV-2 and rhinovirus
- Mucoplasma e.g. Mycobacterium tubercluosis
- Fungi, e.g. , Pneumocystis jiroveci
- Inorganic agents (inhaled dusts or gases) - aspiration pneumonia
Anything that triggers an initial acute inflammatory response in the lungs that activates macrophages and causes neutrophil recruitment.
Opportunistic infections due to weakened immune system
What is the transmission and dissemination of pneumonia?
- Main route - inhalation of pathogens
- Aspiration of oropharyngeal secretions/gastric contents
- Contamination from systemic circulation
- Alcohol : impairs cough reflex - increased aspiration
- Cigarette smoke: reduced mucociliary and macrophage action
What are the classifcations of pneumonia?
-Anatomical classification (how the infection spread in the lungs)
- Clinical setting in which disease occures, what are the circumstances/factors surrounding the disease
- Microbiological , i.e., identifying the causative agent (pathogen)
What are the anatomical classifications of pneumonia?
- Lobar pneumonia - alveoli-alveoli - organsisms access pneumonia and rapidly spread via aleveolar pores (connect adjacent alveoli)
- Seen in adults w/ poor hygeine/malnourished/alcoholic
Bronchopneumonia : bronchi to alveoli
- Organisms colonise bronchi and spread to alveoli
- Affected areas consolidated locally- eventually whole lobes affected
- Seen in young/elderly/immobile
Describe the gross anatomy of lobar pneumonia and bronchopneumonia
Lobar pneumonia:
- Grey hepatization of inferior lobe (whole)
- Bronchopneumonia : Localised solidified masses (sporadic)
What are the clinical setting classifications of pneumonia?
- Community acquired (CAP)
- Hospital acquired (HAP): Nosocomial
- Immuno-compromised
- Aspiration pneumonia
- Necrotising pneumonia & lung abscess
- Chronic pneumonia
What is community acquired pneumonia?
- Strep pneumoniae - most common (gram +ve)
- Haemophilius influenzae and Moraxella catarrhalis - linked to COPD
- Klebsiella pneumoniae - linked to malnourishment and alcoholics (gram neg)
- Pseudomonas aeruginosa - linked to CF and neutropenia - causative agent for hospital acquired pneumonia
- Legionella pneumophila - Legionnaires’ disease
- Viruses e.g. influenza A, rhinovirus, HMPVM SARS - CoV-2
- Bacterial pneumonias are characterised by intra-alveolar neutrophillic inflammation whilst viral pneumonias shows interstitial lymphocytic inflammation
What is Hospital Acquired Pneumonia (HAP)?
- Pulmonary infection acquired during a hospital stay
- Risk factors - underlying disease, immunosuppression, prolonged antibiotic therapym invasive access device, mechanical ventilator (VAP)
- Serious and often life threatening
- Staph aureus - most common (gram +)
- Enterobacteriacae and Pseudomonas species (gram-)
- Patients often have abnormal colonisation of URT with bacteria which colonise LRT if immune resistance lowered
What is immunocompromised pneumonia?
Associated with:
- organ transplants
- Cancer treatments
- Exisitinf immunosuppressive diseases
- Opportunistic infections:
- Bacteria : Mycobacteria
- Viruses : CMV, HSV and VZV
- Fungi : Pneumocystis jiroveci , Candida, Aspergilus
What is Aspiration pneumonia?
- Aspiration of gastric contents:
- Abnormal gag/ swallow reflexes
- Unconsciousness - gastro-oesophageal reflux disease
- Repeated vomitting
- Poor oral hygeine
- Pneumonia is due to both iriitation of gastric contents and bacteria
- Anaerobic bacteria (oral flora)
- Aerobic (S.pneumoniae, S aureus, H influenzam Pseudomonas aeruginosa
- Often necrotising, frequent cause of death and abscess formation in survivors
What is necrotising pneumonia and lung abscesses?
- Rare but severe complication/ progression of pneumonia
- Inflammation and damage results in reduction of vascular supply to tissue- cell death
- Access for antibiotics reduced - infection progrsses
- Frequently causes death (>50% mortlaity)
- Survivors often have lung abcesses
- Aspiration pneumonia = most common precursor pneumonia
- Can resolve with antimicrobial therapy but leaves scarring.
What are the clinical signs and symptoms of pneumonia?
- Fever, chills, dyspnoea
- Severe cough with or without sputum (purulent, bacterialm watery-viral)
- Crackles on auscultation
- Consolidation in radiograph
What is the diagnosis and treatment of pneumonia?
Diagnosis:
- From sputum- bacteria/virus?
Various screening methods: Gram staining, bacterial culture (suitable antibiotic), ELISA, PCR or sequencing
- X tau
- - FBC and pulse oximetry
- Treatment:
- Antibiotic (empirically- can be changed on results)
- Antivirals (uncommon)
