3- pathology of respiratory tract Flashcards
what is pneumonia?
- infection of long parenchyma (functional tissue of an organ)
- infection involving distal airspaces, usually with inflammatory exudation (localised oedema)
what are the classifications of pneumonia by morphology?
- lobar pneumonia (whole lobes)
- bronchopneumonia (bits of lobes)
what are the classifications of pneumonia by clinical setting?
- community
- hospital
= either where infection acquired or how/why patient acquired it - again, doesn’t necessarily tell you what but helps narrow done list
what are the classification of pneumonia by organisms?
stupid question soz - just saying that definitive classification is by what organism caused it = specific treatment can be made
what is lobar pneumonia?
= confluent consolidation involving most/all of lung lobe
- Consolidation is when lung tissue solidified because of accumulation of inflammatory cells, fluid, and debris in alveoli
- areas of consolidation within a lobe merge together to form larger, continuous patches of affected lung tissue
what organisms is most common cause of lobar pneumonia?
strep pneumoniae
(usually community acquired in healthy, younger adult)
what are some less common organisms that can also cause lobar pneumonia?
- Klebsiella pneumoniae - commonly in debilitated or malnourished adults – DM, alcoholics
- Legionella pneumophila – individuals with co-morbidities – heart, renal, haematological disease, immunosuppressed, transplant patients
what is bronchopneumonia?
- infection starts in terminal airways and spreads adjacent to alveolar lung
- widespread, patchy
- often bilateral, basal
what organisms cause bronchopneumonia?
wide variety = strep pneumoniae, haemophilus influenza, staphylococcus, anaerobes, coliforms
what may help narrow down wide variety of organisms that can cause bronchopneumonia?
clinical context may help e.g. staph/anaerobes/coliforms seen in aspiration
when is bronchopneumonia mostly seen in?
most seen in context of pre-existing disease:
- COPD
- Cardiac failure (elderly)
- Complication of viral infection (influenza)
- Aspiration of gastric contents
what is differences in appearance of microscopy in pneumonia stages?
- normally, the alveoli look like big white spaces with thin walls
- during acute period, alveoli filled with neutrophils
- as infection progresses exudate(mostly made of neutrophils but also macrophages, fibrin) within alveoli begins to organise
- exudate becomes formed masses of macrophage & fibroblasts.
= this can either be broken down by enzymes or reabsorbed by phagocytes by macrophages (resolution) or undergo fibrosis (scarring)
what are complications of pneumonia?
- fibrous scarring
- abscess
- empyema
- bronchiectasis
what is a lung abscess?
Localised collection of pus → leads to necrosis of involved lung parenchyma
when do lung abscess mostly occur?
- Most result as a complication of aspiration = foreign material, such as food, liquids, or vomit, is inhaled into the lungs instead of being swallowed into the digestive system →in that case mixed infections so Mixed organisms causing abscess
- Can occur after any bacterial pneumonia
what is empeyema?
- collection of pus in pleural cavity
- can organise leading to fibrous adhesions within pleural cavity
what is bronchiectasis?
- abnormal fixed dilation of bronchi & bronchioles usually due to fibrous scarring following infection (pneumonia, TB, cystic fibrosis) or with tumour
- the dilated airways accumulate purulent secretion and that makes sort of cycle of infection
what is tuberculosis?
chronic pulmonary & systemic disease
- primary infection occurs in lung then chronic infection in many sites (lung, gut, kidneys, lymph nodes, skin)
what is cause of tuberculosis?
mycobacterial infection, commonly:
- Mycobacterium tuberculosis (most common)
- Mycobacterium bovis – infection seen in places with infected dairy cows and no routine pasteurisation of milk (not really seen in scotland)
- Other mycobacteria cause atypical infection especially in immunocompromised host
what helps the pathogenicity of mycobacterium?
- ability to avoid phagocytosis
- ability to stimulate host T cell response
what characterises the pathology of tuberculosis?
- delayed (type IV) hypersensitivity reaction
- granulomatous inflammation which necrosis
= T cell response to organism enhances macrophage ability to kill mycobacteria & T cell response causes granulomatous inflammation, tissue necrosis & scarring
what is primary TB?
what happens in first exposure and up to 5 years afterward
- Inhaled organism phagocytosed and carried to hilar lymph nodes
- Immune activation (few weeks) leads to a granulomatous response in nodes (and in lung) usually leading to killing of organism
*can lead to progressive disease but not very common (5%)
what is secondary TB?
- Reinfection or reactivation of disease in a person with some immunity
- Disease tends initially to remain localised, often in apices of lung
- Can progress to spread by airways and/or bloodstream
why does TB re-activate/re-occur?
you get re-infected as host defences lowered like decreased T cell function (age, coincident disease causing immunocompromised (e.g. HIV), immunosuppressive therapy (steroids, cancer chemotherapy))
usually, where is primary TB?
near pleura, lower part of upper lobe or upper part of lower lobe
what is ghon focus and ghon complex?
- both aspects of primary TB
ghon focus = focused areas of consolidation in lung
ghon complex = ghon focus + enlarged hilar nodes (granulomatous inflammation
what happens to tissues in secondary TB?
fibrosing (scarring + fibrosis) and cavitating apical lesion (lesion that has hollow space in it due to necrosis)
what is the final stage/most severe form of tuberculosis?
= haematogenous (bacteria travels through blood stream to infect different sites of body)
- disseminated TB = miliary TB due to looking like millet seeds - seed like lesions scattered (tiny granulomas)
what is key characteristic of tuberculosis under microscope?
granulomas with caseous necrosis centre
granuloma = aggregate of epithelioid macrophages
*caseous necrosis = think TB
what stain can be used for testing TB?
Ziehl Neelsen (ZN) stain = highlights mycobacteria (small rod shaped organisms staining purple)
stain because alcohol acid fast bacilli = something in cell wall that highlights (called alcohol fast because unlike lots of other organisms retain dye even after alcohol & acid)
what is difference in microscopy for people who are immunocompromised in TB?
can see way more of the purple rods than in normal people with ZN stain
(alveolar spaces also filled with amorphous debris in TB)
what are common pathogens that affect immunocompromised people
a) virus
b) bacteria
c) funghi
d) protozoa
- virus (cytomegalovirus, herpesvirus)
- bacteria (Mycobacterium avium intracellulare)
- fungi (aspergillus, candida, pneumocystis, cryptococcus)
- protozoa (cryptosporidia, toxoplasma)
what is different about symptoms in immunocompromised people?
muted signs or symptoms or completely different ones = High index of suspicion required for diagnosis
what is involved in diagnosis of TB in immunocompromised?
- High index of suspicion
- Multidisciplinary (physician, radiologist, microbiologist, pathologist)
- Broncho-alveolar lavage (BAL) = flushing out airways to try and collect cells & mucus etc
- Cytology/biopsy (with lots of special stains)
what is special stain for pneumocystitis jiroveci?
grocott = stains black when positive
