chest infection

Chest infections

Pathogens
Bacterial pneumonia
Streptococcus pneumoniae (pneumococcus)
Staphylococcus
Pseudomonas
Klebsiella
Chlaymidia
Neisseria meningitides
Haemophilus influenzae
Anaerobes
Legionella
Mycoplasma pneumoniae
Actinomyces israeli
Tuberculosis

Viral pneumonia (25% of community-acquired pneumonias)

Influenza
Varicella, herpes zoster
Rubeola
CMV
Coxsackie, parainfluenza, adenovirus, RSV
Fungal pneumonia
Histoplasmosis
Coccidioidomycosis
Blastomycosis
Aspergillosis
Cryptococcosis
Candidiasis
Zyogomyocoses
Parasitic pneumonias
Pnet~mocystis carinii
Toxoylasma gondii
ACQUISITION OF PNEUMONIA
Community-acquired pneumonia
S. pneumoniae ,, Haemophilus
Mycoplasma
Hospital-acquired pneumonia (incidence 1%, mortality 35%): nosocomial infection
Gram negatives: Pseudomonas, Proteus, E. coli, Enterobacter, Klebsiella


Pneumonia in immunosuppressed patients
Bacterial pneumonia (gram negative) still most common
TB
Fungal
PCP(Pneumocystic carinii pneumonia).
Endemic pneumonias
Fungal: histoplasmosis, coccidioidomycosis, blastomycosis
Viral
Aspiration-associated pneumonia (important)
RISK FACTORS
The radiographic appearance of pulmonary infections is variable depending on
pathogen, underlying lung disease, risk factors, and prior or partial treatment.
Common pathogens associated in community-acquired infections are:
Risk Factor Pathogens I
Alcoholism ===Gram negatives, Strep. pneumoniae, TB, aspiration (mouth flora)
Old age ====Strep. pneumoniae, S. aureus, aspiration
Aspiration ====Mouth flora (anaerobes)
Cystic fibrosis ==Pseudomonas, S. aureus, Aspergillus
Chronic bronchitis ===Strep. pneumoniae, H. influenzae..

Other risk factors for developing pneumonia

Bronchiectasis
Coma, anesthesia, seizures (aspiration)
Tracheotomy
Antibiotic treatment
Immunosuppression (renal failure, diabetes, cancer, steroids, AIDS)
Chronic furunculosis (Staphylococcus)


RADIOGRAPHIC SPECTRUM OF PULMONARY INFECTIONS

TYPE

Pathogen

LOBAR PNEUMONIA

Infection primarily involves alveolus
Spread through pores of Kohn and canals of
Lambert throughout a segment and
ultimately an entire lobe
Bronchi are not primarily affected and remain
air-filled; therefore:
Air bronchograms
No volume loss because airways
are open
Nowadays uncommon due to early treatment
Round pneumonia (children): S. pneumoniae

Type

S. pneumoniae
K. pneumoniae
Others:
S. aureus
H. influenzae
Fungal


BRONCHOPNEUMONIA
Primarily affects the bronchi and adjacent
alveoli
Volume loss may be present as bronchi fill
with exudate
Bronchial spread results in multifocal patchy
Opacities

NODULES

Variable in size
Indistinct margins

CAVITARY LESIONS

Abscess: necrosis of lung parenchyma t
bronchial communication
Fungus ball (air crescent sign)
Pneumatoceles due to air leak into
pulmonary interstitium (S. auueus)

DIFFUSE OPACITIES

Reticulonodular pattern: interstitial
peribronchial areas of inflammation (viral)


Alveolar location (PCP)
Miliary pattern: hematogenous spread (TB)

S. pneumoniae

K. pneumoniae
Others:
S. aureus
H. influenzae

Fungal

S. aureus
Gram negatives
Other:
H. influenzae
Mycoplasma
Fungal
Histoplasma
Aspergillus
C yptococcus
Coccidi~ides
Bacterial
Legionella
Nocardia
Septic emboli
S. aureus


Anaerobes
Fungal
TB

Viral

Mycoplasma

PCP
Complications of Pneumonia
Parapneumonic effusion
Stage 1: exudation: free flowing
Stage 2: fibropurulent: loculated
Stage 3: organization, erosion into lung or chest wall
Empyema
Bronchopleural fistula (fistula between bronchus and pleural space) with
eroding pleural-based fluid collections
Bronchiectasis
Pulmonary fibrosis, especially after necrotizing pneumonia or ARDS
Adenopathy..

RESOLUTION OF PNEUMONIA

80% to 90% resolve within 4 weeks
5% to 10% resolve within 4 to 8 weeks (usually in older or diabetic patients).
Subsequent films should always show interval improvement compared to the
prior films.
Nonclearance
Antibiotic resistance
Consider other pathogen, (e.g., TB)
Recurrent infection
Obstruction pneumonitis due to tumor


Bacterial Infections

Common pathogens

S. pneumoniae, 50% (40-60 years)
Mycoplasma, 30%
Anaerobes, 10%
Gram negatives, 5%
Staphylococcus, 5%
Haemophiltis, 3% (especially in infants and patients with COPD)
Clinical findings
Pneumonic syndrome
Fever
Cough
Pleuritic pain
Sputum
Ancillary findings
Headache, arthralgia, myalgia
Diarrhea
Hemoptysis
STREPTOCOCCAL PNEUMONIA


Radiographic features
Lobar or segmental pneumonia pattern
Bronchopneumonia pattern
Round pneumonia (in children)

STAPHYLOCOCCAL PNEUMONIA

Radiographic features
Bronchopneumonia pattern
Bilateral in > 60%
Abscess cavities in 25%-75%
Pleural effusion, empyema, 50%
Pneumatoceles, 50% (check valve obstruction), particularly in children
Central lines
Sign of endocarditis

PSEUDOMONAS PNEUMONIA

Typical clinical setting
Hospital-acquired infection
Ventilated patient
Reduced host resistance
Patients with cystic fibrosis
Radiographic features
Three presentations:
Extensive bilateral parenchymal consolidation (predilection for both lower
lobes)
Abscess formation
Diffuse nodular disease (bacteremia with hematogenous spread; rare)
LEGIONNAIRES' DISEASE
Severe pulmonary infection caused by Legionella pneumophila; 35% require ventilation,
20% mortality. Most infections are community acquired. Patients have hyponatremia.
Seroconversion for diagnosis takes 2 weeks.
Radiographic features
Common features
Initial presentation starts as peripheral patchy consolidation
Bilateral severe disease
Rapidly progressive
Pleural effusions < 50%
Lower lobe predilection
Uncommon features
Abscess formation
Lymph node enlargement
HAEMOPHILUS PNEUMONIA
Caused by Hnemophilus influenzne. Occurs most commonly in children, immunocompromised
adults or patients with COPD. Often there is concomitant meningitis,
epiglottitis, bronchitis.


Radiographic features
Bronchopneumonia pattern
Lower lobe predilection, often diffuse
Empyema

TUBERCULOSIS (TB)

Transmitted by inhalation of infected droplets Mycobacterium tuberculosis or M. bovis.
TB usually requires constant or repeated contact with sputum-positive patients as
the tubercle does not easily grow in the immunocompetent human host. Target
population:
Patients of low socioeconomic scale (homeless)
Alcoholics
Immigrants: Mexico, Philippines, Indochina, Haiti
Elderly patients
AIDS patients
Prisoners
Primary infection

Usually heals without complications. Sequence of events:

Pulmonary consolidation (1-7 cm); cavitation is rare; lower lobe
(60%) > upper lobes
Caseous necrosis 2-10 weeks after infection
Lymphadenopathy (hilar and paratracheal), 95%
Pleural effusion, 10%
Spread of a primary focus occurs primarily in children or immunosuppressed
patients


Secondary infection (Reactivation TB)

Active disease in adults most commonly represents reactivation of a

primary focus. However, primary disease is now also common in adults in
developed countries since there is no exposure in childhood. Distribution
is as follows:
Typically limited to apical and posterior segments of upper lobes or
superior segments of lower lobes (because high PO,?)
Rarely in anterior segments of upper lobes (in contradistinction to
Consolidation
scarring
histoplasmosis)

Radiographic features

Exudative tuberculosis
Patchy or confluent airspace disease
Adenopathy is uncommon
Fibrocalcific tuberculosis
Sharply circumscribed linear densities radiating to hilum
Cavitation, 40%


Complications
Miliary TB may occur after primary or secondary hematogenous spread
Bronchogenic spread occurs after communication of the necrotic area with a
bronchus; it produces an acinar pattern (irregular nodules approximately 5 mm
in diameter)
Tuberculoma (1-7 cm): nodule during primary or secondary TB; may contain
calcification
Effusions are often loculated
Bronchopleural fistula
Pneumothorax

COMPARISON

Primary TB Reinfection TB
Location Usually bases Upper lobes, sup. segment LL
Appearance Focal Patchy
Cavitation No Frequent
Adenopathy as only Common NO
Finding
Effusion Common Uncommon
Miliary pattern Yes Yes
PULMONARY ABSCESS:
The spectrum of anaerobic pulmonary infections includes:
Abscess: single or multiple cavities > 2 cm, usually with air-fluid level
Necrotizing pneumonia: analogous to abscess but more diffuse and cavities
<2cm
Empyema: suppurative infection of the pleural space, most commonly as a
result of pneumonia.
Predisposing conditions
Aspiration (alcoholism, neurologic disease, coma, etc.)
Intubation
Bronchiectasis, bronchial obstruction
Treatment:
Antibiotics, postural drainage
Percutaneous drainage of empyema
Drainage/resection of lung abscess only if medical therapy fails.
Viral Pneumonia
Spectrum of disease
Acute interstitial pneumonia: diffuse or patchy interstitial pattern, thickening of
bronchi, thickened interlobar septae
Lobular inflammatory reaction: multiple nodular opacities 5-6 mm (varicella;
late calcification)
Hemorrhagic pulmonary edema: mimics bacterial lobar pneumonia
Pleural effusion: usually absent or small
Chronic interstitial fibrosis (broncholitis obliterans).
INFLUENZA PNEUMONIA
Influenza is very contagious and thus occurs in epidemics. Pneumonia, however, is
uncommon.
Radiographic features
Acute phase: multiple acinar densities
Coalescence of acinar densities to diffuse patchy air space disease
(bronchopneumonia type).


Fungal infection

Radiographic features

Acute phase: pneumonic type of opacity (may be segmental, nonsegmental, or
patchy); miliary (hematogenous) distribution in immunosuppressed patients
Reparative phase: nodular lesions with or without cavitations and crescent sign
Chronic phase: calcified lymph nodes or pulmonary focus with fungus (e.g.,
histoplasmosis)
Disseminated disease (spread to other organs) occurs primarily in
immunocompromised patients.