Lung abscess is a cavitary lesion containing purulent material resulting from necrotizing infection in the lung parenchyma. Most commonly caused by aspiration (alcoholism, loss of consciousness, swallowing dysfunction) and anaerobic bacteria (Bacteroides, Fusobacterium, Peptostreptococcus). Incidence is 4-5 per 100,000. It is 3-4 times more common in males with mean age 50-60 years. The right lung is affected more often than the left (increased aspiration risk due to the more vertical angle of the right main bronchus). Mortality has decreased to 5-10% in the antibiotic era but may reach 20-30% in immunosuppressed patients.
Age Range
30-70
Peak Age
50
Gender
Male predominant
Prevalence
Uncommon
Lung abscess most commonly develops through aspiration mechanism — oropharyngeal secretions (dense in anaerobic flora) are aspirated into the lower airways during loss of consciousness, alcoholism, or neurological impairment. Bacteria initiate necrotizing pneumonia in the lung parenchyma — proteolytic enzymes and toxins cause tissue necrosis. The necrotic area liquefies and an inflammatory wall (pyogenic membrane) forms around it — this determines the CT appearance of the thick irregular wall. When the cavity communicates with the bronchial tree, necrotic material partially drains and air enters — creating an air-fluid level. Aspiration abscess characteristically locates in gravity-dependent segments: in supine position, right upper lobe posterior segment and lower lobe superior segment. It forms an acute angle with the pleura (distinguishing from empyema). Wall enhancement reflects the intense vascularity and active inflammation of the pyogenic membrane.
The triad of thick irregular-walled cavitary lesion, air-fluid level, and acute angle with the pleural surface — pathognomonic imaging combination of lung abscess. This triad distinguishes from empyema (obtuse angle, lentiform, split pleura sign), cavitary carcinoma (irregular inner wall, but no fever/leukocytosis), and cavitary metastasis (known primary, multiple).
Thick (>4 mm), irregular-walled cavitary lesion. Wall thickness usually varies between 5-15 mm. Inner wall surface may be irregular/nodular. Outer margin becomes indistinct due to surrounding parenchymal consolidation. The wall shows intense enhancement (pyogenic membrane).
Report Sentence
A cavitary lesion measuring approximately ___ cm in the ___ lobe with thick irregular wall and intense wall enhancement is identified, consistent with lung abscess.
Air-fluid level — a flat line between purulent fluid (high density) and air above (low density) within the cavity. Indicates communication of the abscess cavity with the bronchial tree. Air-fluid level is best evaluated on supine CT or lateral decubitus position.
Report Sentence
Air-fluid level within the cavity is identified, consistent with lung abscess with bronchial communication.
Acute angle with pleura — abscess maintains round/oval shape and forms an acute angle with the pleural surface. Empyema shows lentiform (lens) shape and forms an obtuse angle with the pleural surface. 'Split pleura sign' is seen in empyema (separate enhancement of visceral and parietal pleura), absent in abscess.
Report Sentence
The cavitary lesion forms an acute angle with the pleural surface, favoring intraparenchymal abscess; empyema (obtuse angle, lentiform shape) has been morphologically excluded.
Extensive consolidation area surrounding the cavity — reflecting the necrotizing pneumonia background. Consolidation may contain air bronchograms. Ground-glass opacities and septal thickening may be observed in surrounding parenchyma (perifocal inflammatory changes).
Report Sentence
Extensive consolidation area surrounding the cavitary lesion is identified, consistent with necrotizing pneumonia/abscess.
Abscesses near the pleural surface can be evaluated by US: hypoechoic, heterogeneous collection (purulent material), with hyperechoic foci within (gas bubbles, 'dirty shadowing'). Doppler may show periwall hypervascularity. US is also used for percutaneous drainage guidance.
Report Sentence
A pleural-based hypoechoic heterogeneous collection with gas echoes within is identified on US, consistent with lung abscess.
Criteria
Caused by aspiration mechanism. In the setting of alcoholism, loss of consciousness, neurological impairment. Anaerobic bacteria predominant.
Distinct Features
Gravity-dependent segment location (supine: right upper lobe posterior, lower lobe superior). Usually solitary. Good response to antibiotic treatment (80-90%). Polymicrobial (anaerobes + aerobes).
Criteria
Developing distal to bronchial obstruction. In the setting of endobronchial tumor (most common), foreign body, or stricture.
Distinct Features
Non-gravity-dependent segment location. Endobronchial lesion should be sought — intrabronchial mass on CT. Slow/insufficient response to antibiotic treatment (due to obstruction). Cavitary lesion in smoker >50 years — cancer must be excluded.
Criteria
Originating from septic emboli. In the setting of IV drug use, infective endocarditis, thrombophlebitis. S. aureus most common pathogen.
Distinct Features
Multiple, bilateral, peripherally located cavitary nodules. 'Feeding vessel sign' — indicating hematogenous origin of septic emboli. Early stage: solid nodule surrounded by ground-glass halo, late stage: cavitation. Subpleural location predominant.
Distinguishing Feature
Cavitary squamous carcinoma shows irregular thick wall and nodular inner surface but surrounding consolidation is less prominent; abscess shows more extensive consolidation and air-fluid level. Clinical context: cancer — elderly smoker, abscess — fever, leukocytosis, aspiration history.
Distinguishing Feature
TB cavity in the upper lobe apex, thin smooth wall, surrounding satellite nodules and tree-in-bud pattern; abscess has thick irregular wall surrounded by extensive consolidation. Air-fluid level is less common in TB.
Distinguishing Feature
Aspergilloma shows a freely mobile fungus ball within a pre-existing cavity (TB, bronchiectasis) with 'air crescent sign'; in abscess the air-fluid level is horizontal and the cavity wall shows active inflammatory enhancement.
Urgency
urgentManagement
medicalBiopsy
Not NeededFollow-up
6-monthLong-term antibiotic therapy (4-8 weeks IV + oral) is the primary approach in lung abscess treatment — empiric anaerobic coverage for aspiration abscess (clindamycin or amoxicillin-clavulanate). 80-90% of patients respond to medical treatment. Percutaneous drainage: indicated for >6 cm abscesses, cases unresponsive to medical treatment, or sepsis development. Surgical resection: performed for medical+drainage failure, massive hemoptysis, or suspicion of occult malignancy underlying the abscess. In post-obstructive abscess, bronchoscopy should exclude endobronchial pathology. Follow-up CT at 4-6 weeks evaluates treatment response — cavity shrinkage and wall thinning are expected.
Antibiotic therapy is the mainstay (4-6 weeks). Percutaneous or surgical drainage may be needed for large abscesses. Underlying bronchial obstruction (tumor) should be excluded.