Pathology of Lung Infection Flashcards
What is pneumonia?
Inflammation of the lung - mostly due to infection but not always
What are the clinical features of pneumonia?
Fever and chills, unrelenting cough, sputum production (yellow or green), chest pain if pleura is inflamed, impaired gas exchange resulting in dyspnoea and tachypnoea
What are the three groups of pneumonia according to clinical setting?
Community acquired, hospital acquired or compromised immune host
What pathogen is most likely to cause community acquired pneumonia?
50% of cases are caused by streptococcus pneumoniae
What pathogen is most likely to cause hospital acquired pneumonia?
A gram negative bacteria
What pathogens are more likely in immune compromised hosts to cause pneumonia?
Fungi or protozoa (pneumocystis jirovecii)
What are the four ways which pathogens can reach the lung?
Inhalation of pathogens in air droplets, aspiration of infected secretions from the URT, aspirating infected particles like gastric contents or food or drink, from the blood
What are the three classes of pathogens causing pneumonia?
upper respiratory tract flora, enteric saprophytes, extraneous pathogens
What are the upper respiratory tract flora which can cause pneumonia?
Streptococcus pneumoniae, haemophilus influenzae, staphlococcus aureus
What are the enteric saprophytes which can cause pneumonia?
E. coli, pseudomonas
What are the extraneous pathogens which can cause pneumonia?
Legionella pneumophila, tuberculosis
What are the two patterns of infective pneumonia?
Alveolar inflammation or interstitial inflammation (atypical pneumonia)
What cells are involved in alveolar inflammation?
Neutrophils in the alveolar spaces (consolidation)
What pathogens cause alveolar inflammation?
bacterial pathogens such as streptococcus, staphylococcus, haemophilus, gram negatives
What are the two kinds of alveolar inflammation?
Bronchopneumonia and lobar pneumonia
What is the pattern of consolidation in bronchopneumonia?
Patchy and bilateral
What is the pattern of consolidation in lobar pneumonia?
Entirety of a single lobe
What does consolidation look like on a CXR?
White
What does consolidation look like macroscopically?
White and solid
What is the commonest cause of lobar pneumonia?
streptococcus pneumoniae
What is the commonest way to get strep pneumoniae lobar pneumonia?
community acquired
What are the symptoms of community acquired strep pneumoniae lobar pneumonia?
high fever with chills, raised white cell count, cough, pleuritic chest pain, blood stained sputum, gram positive diplococci present in sputum, often causes bacteraemia
What are the 4 stages of lobar pneumonia?
congestion, red hepatisation, grey hepatisation, resolution
What happens in congestion?
Protinaceous exudate full of diplococci in the alveoli
What happens in red hepatisation?
Consolidation with haemorrhage into airspaces
What happens in grey hepatisation?
mesh work of fibrin in alveolar spaces with neutrophils and macrophages
Which patients most commonly get bronchopneumonia?
Young and old patients or patients with chronic disease e.g. COPD, cardiac failure, malignancies or cystic fibrosis - hospitalised patients
What pathogens most commonly cause bronchopneumonia?
gram negative bacteria - pseudomonas or staphylococcus
What are the complications of pneumonia?
Pleurisy, pyothorax, empyema, abscess, bronchiecstasis, fibrosis, cysts
What is a lung abscess?
A cavity containing puss
What pathogen almost always causes lung abscess?
Staphylococcus aureus
What are other causes of lung abscess?
aspiration of infected contents from the URT such as gastric contents, distal to bronchial obstruction by a tumor, septic emboli to the lung
What cells are involved in atypical pneumonia?
Lymphocytes and macrophages in intra alveolar septa
What pathogens cause atypical pneumonia?
Viruses, bacteria (mycoplasma pneumonia, coxiella burnetti, legionella, chlamydia pneumoniae)
What is seen in the lung macroscopically in atypical pneumonia?
lung looks dark, wet and heavy - there is no consolidation
What is the clinical presentation of atypical pneumonia?
systemic symptoms more than respiratory systems - malaise, aches, pains, headache, diarrhoea, non productive cough - ‘walking pneumonia’
What does the CXR of atypical pneumonia look like?
Dots and dashes in both lung fields
What is tuberculosis?
a chronic granulomatous pneumonia due to infection with mycobacterium tuberculosis
What are the unique features of tuberculosis compared to other bacterial pneumonias?
the human body cannot eradicate it, and it can lie dormant after the initial infection before causing a secondary infection
What are the clinical features of primary TB?
mild often asymptomatic
What are the histological features of primary TB?
Ghon’s complex
What is a Ghon’s complex?
Ghon focus + involved hilar lymph node
What is a Ghon’s focus?
Granuloma (aggregate of epithelioid macrophages + multinucleate macrophages) around caseous necrosis
What causes the granuloma?
A type IV hypersensitivity response where monocytes under the influence of IGNgamma become epithelioid macrophages
How does primary TB resolve?
The immune response controls the infection and the Gohn complex heals by fibrosis, often with some calcification
What is secondary TB?
The reactivation of a dormant infection or a reinfection
What area of the lung does secondary TB effect?
Lobar pneumonia involving the upper lobe
What macroscopic features are seen in secondary TB?
casseous necrosis, fibrosis, calcification, cavitation (where caseation erodes into a bronchus)
What are the complications of secondary TB?
Spread into surrounding lung, erosion of blood vessels, erosion into bronchial tree causing spread, pleural inflammation and fibrosis, lung scarring
How is TB spread from person to person?
infected aerosolised droplets
What are the clinical features of secondary TB?
weight loss, malaise, fevers, night sweats, haemoptysis, dyspnoea and chronic cough
What are the features of mycobacterium tuberculosis?
aerobic rods with an acid fast wall - detected by ZN stain
How does TB spread around the body?
Via lymphatics to pleura or to the opposite lung, via the bronchial tree - can be coughed up into larynx and swallowed and become intestinal - or can spread via the blood stream to other organs
What is miliary TB?
progressive tuberculosis caused by spread through the blood stream where multiple organs are involved - macroscopically you see numerous small white granulomas in the organs
What is single organ TB?
Where a single organ is infected in primary TB but lies dormant and then when becomes activated has effect on only one organ e.g. Potts disease in the spine
