Pneumonias and Fungal
infections
Dr.FARHANA ZAKARIA
PNUEMONIA
• Defined as acute infection of the lung
parenchyma distal to the terminal bronchioles
Pathogenesis
• Microorganisms gain entry into the lungs by
one of the following routes :
• Inhalation of microbes present in air
• Aspiration of organisms from the nasopharynx
or oropharynx
• Hematogenous spread from a distant focus of
infection
• Direct spread from an adjoining site of
infection.
Etiologic classification of pneumonias
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BACTERIAL PNEUMONIA
Lobar pneumonia
Bronchopneumonia
VIRAL AND MYCOPLASMAL PNEUMONIA
OTHER TYPES OF PNEUMONIAS
Pneumocystis carini pneumonia
Legionella pneumonia
Aspiration pneumonia
Anatomical classification
• Lobar pneumonia
• Broncho pneumonia
• Interstitial pneumonia
Bacterial pneumonia
• Most common cause of pneumonia
Lobar pneumonia
• Is an acute bacterial infection of a part of a
lobe , the entire lobe or even two lobes of one
or both the lungs
• Lower lobes are affected most commonly
• Etiology
• Pneumococcal pneumonia – more than 90%
of all lobar pneumonias are caused by
streptococcus pneumoniae .
• Is community acquired infection
• Staphylococcal pneumonia – staphylococcus
aureus causes pneumonia by hematogenous
spread of infection.
• Streptococcal pneumonia – β-hemolytic
streptococci cause pneumonia in severely
debilitated elderly patients and in diabetics
• Pneumonia by gram-negative aerobic bacteria
• Like haemophilus influenza , klebsiella
pneumonia, pseudomonas, proteus , E coli ,
H.influenza.
Morphologic features
• Lobar pneumonia can be divided into 4
sequential pathologic phases:
• Stage of congestion
• Red hepatisation
• Grey hepatisation
• Resolution
Stage of congestion – initial phase
• Represents early acute inflammatory response
to bacterial infection and lasts for 1 to 2 days.
• Grossly – affected lobe is enlarged , heavy ,
dark red and congested .
• C/S exudes blood-stained frothy fluid
• Histologically :
• Dilatation and congestion of capillaries in the
alveolar walls.
• Pale eosinophilic edema fluid in the air spaces
• Few red cells and neutrophils in the intraalveolar fluid.
• Numerous bacteria demonstrated in the
alveolar fluid by gram’s staining.
Red hepatisation – early consolidation
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Lasts for 2 to 4 days
Liver-like consistency of afected lobe on C/S
Grossly:
Affected lobe is red , firm and consolidated
C/S of involved lobe is airless , red-pink , dry ,
granular and has liver-like consistency
• Accompanied by serofibrinous pleurisy.
• Histologically ,
• Edema fluid of preceding stage is replaced by
strands of fibrin
• Marked cellular exudate of neutrophils and
extravasation of red cells
• Many neutrophils show ingested bacteria
• The alveolar septa are less prominent than in
the first stage due to cellular exudation.
Grey hepatisation – late consolidation
• This phase lasts for 4 to 8 days
• Grossly , the affected lobe is firm and heavy.
• C/S is dry, granular and grey in appearance
with liver-like consistency .
• Change in color from red to grey begins at
hilum and spreads towards the periphery .
• Fibrinous pleurisy is prominent.
• Histologically,
• Fibrin strands are dense and more numerous
• Cellular exudate of neutrophils is reduced due to
disintegration of many inflammatory cells. Red
cells are also fewer.
• Macrophages begin to appear in the exudate
• Cellular exudate is often separated from the
septal walls by a thin clear space.
• Organisms are less numerous and appear as
degenerated forms.
Resolution
• This stage begins by 8th to 9th day if no
chemotherapy is administered and completed
in 1 to 3 weeks.
• Grossly ,
• Previously solid fibrinous constituent is
liquefied by enzymatic action , eventually
restoring normal aeration in the affected lobe.
• Process of softening begins centrally and
spreads to periphery.
• C/S is grey- red or dirty brown and frothy ,
yellow , creamy fluid can be expressed on
pressing.
• Pleural reaction may also show reaction but
may undergo organisation leading to fibrous
obliteration of pleural cavity.
• Histologically ,
• Macrophages are predominant cells in the
alveolar spaces , neutrophils diminish in
number.
• Granular and fragmented strands of fibrin in
the alveolar spaces are seen
• Alveolar capillaries are engorged
• There is progressive removal of fluid content
as well as cellular exudate from the air spaces.
Complications
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Organisation
Pleural effusion
Empyema
Lung abscess
Metastatic infection
Bronchopneumonia
• Infection of terminal bronchioles that extends
into surrounding alveoli resulting in patchy
consolidation of lung.
• Frequent at extremes of life , as a terminal event
in chronic debilitating diseases and as a
secondary infection following viral respiratory
infections
• Common organisms- staphylococci , streptococci ,
pneumococci , klebsiella pneumonia,
haemophilus influenza , pseudomonas.
Gross
• Patchy areas of red or grey consolidation
affecting one or more lobes , frequently found
bilaterally and more often involving lower
zones of the lungs .
• C/S – dry , granular , firm , red or grey in color
, 3 to 4 cms in diameter , slightly elevated over
the surface and are often centered around a
bronchiole.
Histologically
• Acute bronchiolitis
• Suppurative exudate in the peribronchiolar
alveoli
• Thickening of the alveolar septa by congested
capillaries and leucocytic infiltration
• Less involved alveoli contain edema fluid.
Fungal infections of lung
• More common than tuberculosis in US.
• These infections in healthy individuals are
rarely serious but in immunosuppressed
individuals may prove fatal
Histoplasmosis
• Caused by histoplasma capsulatum
• By inhalation of infected dust or bird
droppings.
• May remain asymptomatic or may produce
lesions similar to ghon’s complex.
Coccidioidomycosis
• Caused by coccidioides immitis , spherical
spores
• Infection is acquired by close contact with
infected dogs.
• Lesions consist of peripheral parenchymal
granuloma in the lung
Cryptococcosis
• Caused by cryptococcus neoformans which is
round yeast having a halo around it due to
shrinkage in tissue sections.
• Infections occurs by inhalation of pigeon
droppings.
• Lesions range from small parenchymal
granuloma in the lung to cryptococcal
meningitis.
Blastomycosis
• Caused by blastomyces dermatitidis.
• Result from inhalation of spores in the ground.
• May present as ghon’s complex-like lesion , as
a pneumonic consolidation , and as multiple
skin nodules.
Aspergillosis
• Most common fungal infection of the lung
caused by aspergillus fumigatus.
• Fungus exists as a thin septate hyphae with
dichotomous branching and grows best in
cool , wet climate.
• Result in allergic bronchopulmonary
aspergillosis , aspergilloma and necrotising
bronchitis.
• Immunocompromised persons develop more
serious manifestations of aspergillus infection.
Mucormycosis
• Caused by Mucor and Rhizopus.
• Pulmonary lesions are especially common in
patients with diabetic ketoacidosis.
Candidiasis
• Caused by candida albicans.- normal
commensal in oral cavity, gut and vagina.
• Attains pathological forms in
immunocompromised host.
• Angio-invasive growth of the organism occurs
in the airways.