Lung Abscess
Characteristics
1. Cavitating
infective consolidation.
2. Single
or multiple lesions.
3. Bacterial
(Staphylococcus aureus, Klebsiella, Proteus, Pseudomonas, TB and anaerobes) or
fungal pathogens are the most common causative organisms.
4. ‘Primary’ lung abscess – large solitary
abscess without underlying lung disease is usually due to anaerobic bacteria.
5. Associated
with aspiration and/or impaired local or systemic immune response (elderly,
epileptics, diabetics, alcoholics and the immunosuppressed).
Clinical
features
1. There
is often a predisposing risk factor, e.g. antecedent history of aspiration or
symptoms developing in an immunocompromised patient.
2. Cough
with purulent sputum.
3. Swinging
pyrexia.
4. Consider
in chest infections that fail to respond to antibiotics.
5. It
can run an indolent course with persistent and sometimes mild symptoms. These
are associated with weight loss and anorexia mimicking pulmonary neoplastic
disease or TB infection.
Radiological
features
1. Most
commonly occur in the apicoposterior aspect of the upper lobes or the apical
segment of the lower lobe.
2. CXR
may be normal in the first 72 h.
3. CXR
– a cavitating essentially spherical area of consolidation usually >2 cm in
diameter, but can measure up to 12 cm. There is usually an air-fluid level
present.
4. Characteristically
the dimensions of the abscess are approximately equal when measured in the
frontal and lateral projections.
5. CT
is important in characterising the lesion and discriminating from other
differential lesions. The abscess wall is thick and irregular and may contain
locules of free gas. Abscesses abutting the pleura form acute angles. There is
no compression of the surrounding lung. The abscess does not cross fissures. It
is important to make sure no direct communication with the bronchial tree is
present (bronchopleural fistula).
Fig:
Lung abscess – frontal and lateral views. Cavitating lung abscess in the left
upper zone.
Differential
diagnosis
1. Bronchopleural
fistula – direct communication with bronchial tree. Enhancing split pleural
layers on CT.
2. Empyema
- enhancing split pleural layers, forming obtuse margins with the lung on CT.
3. Primary
or secondary lung neoplasms (e.g. squamous cell carcinomas) these lesions can
run a slow indolent course. Failure to respond to antibiotic therapy should
alert the clinician to the diagnosis.
4. TB
(usually reactivation) – again suspected following slow response to treatment.
Other findings on the CT may support old tuberculous infection such as lymph
node and/or lung calcification. Lymphadenopathy, although uncommon, may be
present on the CT scans in patients with lung abscesses. It is therefore not a
discriminating tool for differentiating neoplasms or TB infection.
Management
1. Sputum
– M, C & S.
2. Protracted
course of antibiotics is usually a sufficient treatment regime.
3. Physiotherapy
may be helpful.
4. Occasionally
percutaneous drainage may be required.
5. Lastly,
some lesions failing to respond to treatment and demonstrating soft tissue
growth or associated with systemic upset (e.g. weight loss) may need biopsy.
This is done to exclude underlying neoplasm (e.g. squamous cell carcinoma).
Reference:
·
Andrew P., Mangerira C. and Rakesh R. A-Z Chest Radiology, pp.22-24
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