PassFinals
Respiratory

Lung Abscess

A lung abscess is a localised collection of pus within necrotic lung parenchyma, commonly following aspiration of oral flora; it presents subacutely with fever and purulent or foul sputum, and requires prolonged specialist antimicrobial treatment while excluding empyema, obstruction, malignancy, tuberculosis and septic emboli.

In a nutshell

A lung abscess is a pus-filled cavity within necrotic lung, commonly following aspiration of oral flora. It presents subacutely with fever, purulent or foul sputum and a thick-walled cavity with an air-fluid level. Treat urgently with specialist-guided prolonged antimicrobial therapy, investigate the cause and escalate for drainage, bronchoscopy or surgery when medical treatment fails.

Classic presentation

A person with aspiration risk and poor dentition has a subacute febrile illness, weight loss and foul productive cough; imaging shows a thick-walled intraparenchymal cavity with an air-fluid level.

Key points

  • Aspiration is common, but obstruction, malignancy, septic emboli, tuberculosis and atypical infection must remain in the differential.
  • The classic radiograph is a thick-walled intraparenchymal cavity with an air-fluid level; CT distinguishes it from empyema and looks for obstruction.
  • Use specialist-guided prolonged antimicrobial therapy with appropriate anaerobic coverage when indicated; duration follows clinical, biochemical and radiological response.
  • Most primary abscesses do not need immediate drainage, but persistent sepsis or non-resolution requires respiratory, microbiology and interventional review.
  • An empyema is pleural, whereas a lung abscess is intraparenchymal; pleural infection needs pleural source control.

First-line investigation

Chest radiograph followed by contrast CT to confirm an intraparenchymal cavity, identify complications and exclude obstruction or malignancy; send sputum and blood cultures when indicated.

Management

Stabilise and start targeted antibiotics

  • Treat sepsis promptly, obtain samples where safe and start local, culture-informed antimicrobial therapy with BNF and microbiology input.4,3,6

Confirm the cavity and cause

  • Use chest radiography and contrast CT, send respiratory/blood microbiology and assess aspiration, obstruction, cancer, TB, fungal disease and septic emboli.1,2,3

Support clearance and prevent recurrence

  • Provide oxygen, analgesia, fluids, nutrition and appropriate physiotherapy while addressing dysphagia, reduced consciousness, poor dentition and other aspiration risks.3,4,7

Drain or sample non-resolving disease

  • Discuss image-guided or endobronchial drainage, bronchoscopy and surgical options when there is persistent sepsis, failure of appropriate therapy, haemorrhage, obstruction or a bronchopleural fistula.1,2,5

Document radiological and clinical resolution

  • Follow symptoms, inflammatory markers and interval imaging; a persistent cavity or atypical course needs renewed investigation rather than automatic antibiotic extension.1,3

Exam traps

  • A cavity with an air-fluid level is not automatically an abscess; consider cancer, TB, fungal infection, infected bulla and septic emboli.
  • Use CT to distinguish a rounded intraparenchymal abscess from a pleural empyema.
  • Do not confuse aspiration pneumonitis with established infected necrosis; chemical pneumonitis alone does not require prophylactic antibiotics.
  • Persistent fever or a non-resolving cavity requires specialist reassessment, not simply a longer unreviewed antibiotic course.
  • Treat the aspiration risk and search for endobronchial obstruction, particularly in an older smoker.

Illustrations

Lung abscess on chest radiographA chest radiograph showing a thick-walled intraparenchymal cavity containing a horizontal air-fluid level in a dependent lung segment.James Heilman, MD, Wikimedia Commons · CC-BY-SA-4.0
Cavitating lung abscess on CTAn axial lung-window CT showing a thick-walled intraparenchymal cavity with an air-fluid level and surrounding consolidation, consistent with a lung abscess.James Heilman, MD, Wikimedia Commons · CC-BY-SA-4.0

Key sources

  1. Buckinghamshire Formulary, Management and antibiotic therapy for respiratory tract conditions in adults (UK NHS adult respiratory antimicrobial guidance covering lung-abscess microbiology, specialist review, prolonged response-guided therapy and drainage/alternative-diagnosis considerations)
  2. NHS Grampian, Orkney and Shetland, Lung abscess antimicrobial guidance (Current NHS antimicrobial page identifying common organisms, urgent chest-physician referral, sputum sampling and specialist-directed duration/therapy)
  3. NICE NG250, Pneumonia: diagnosis and management (Current NICE pneumonia assessment, imaging, severity, antimicrobial, hospital and reassessment pathway; published 2 September 2025)Published 2 Sept 2025
  4. NICE NG253, Suspected sepsis in people aged 16 or over (Current adult sepsis recognition, investigation, antimicrobial, source-control, monitoring and escalation pathway; published 19 November 2025)Published 19 Nov 2025
  5. British Thoracic Society, BTS Guideline for Pleural Disease (Current UK pleural-infection and empyema pathway used to distinguish pleural source control from an intraparenchymal abscess; published July 2023)Published 1 Jul 2023
  6. BNF, antibacterial drugs and respiratory infections (Current UK prescribing, contraindication, interaction, monitoring and patient-specific dosing reference; access may require subscription or institutional login)
  7. NHS Highland, Aspiration pneumonia antimicrobial guidance (Current NHS guidance distinguishing aspiration pneumonitis from infection and reserving additional anaerobic cover for high-risk features such as suspected lung abscess or empyema)

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.