Lung Abscess

Overview

Localised necrosis+suppuration of lung tissue. Primary (normal lung, usually aspiration) vs Secondary (complicates another lung disease/distant site).

Etiopathogenesis

Isolates: strep, staph, gram-negatives. 5 routes:

Aspiration — food, decaying teeth, gastric contents, infected gingivae, necrotic oral/URT tissue. Favoured by sleep, unconsciousness, anaesthesia, debility, alcoholism
Preceding bacterial infection — bronchopneumonia (debilitated patient); occasionally TB, bronchiectasis, mycotic infection
Bronchial obstruction — distal to tumour/foreign body
Septic embolism — pyaemia/thrombophlebitis/endocarditis → right heart → lung → MULTIPLE abscesses
Misc — infected pulmonary infarcts, amoebic abscess (E. histolytica), trauma, direct extension from mediastinum/oesophagus/subphrenic/spine

Morphology

Distribution: aspiration abscesses → RIGHT lung (more vertical main bronchus), usually SINGLE, lower part of RUL or apex of RLL. Post-pneumonia/septic abscesses → often MULTIPLE, scattered.

Gross: few mm to 5-6cm cavities with exudate. Acute: surrounded by acute pneumonia, poorly-defined ragged wall. Chronic: fibrous wall.

Micro: parenchyma destruction + suppurative exudate. Initially acute inflammation surround → later chronic infiltrate (lymphocytes/plasma cells/macrophages) → chronic cases: fibroblastic proliferation, fibrocollagenic wall.

Clinical features

Fever, malaise, weight loss, cough, purulent expectoration, haemoptysis (~half). Clubbing (~20%). Secondary amyloidosis in chronic longstanding cases (same mechanism as bronchiectasis).

Clinical relevance

Right-lung predominance = simple anatomic fact (more vertical main bronchus, in line with trachea) — same logic explains right-sided predominance across multiple aspiration-related conditions, not just abscess. Single (aspiration) vs multiple (septic embolic) = practical diagnostic clue — multiple abscesses should prompt search for distant septic source (endocarditis, thrombophlebitis, pyaemia). Wall evolution (ragged acute → fibrocollagenic chronic) mirrors general acute-to-chronic inflammation pattern — instance of a general process, not lung-abscess-specific. Secondary amyloidosis = recurring theme across suppurative lung disease (also in bronchiectasis) — sustained inflammatory stimulation is the shared driver regardless of initiating disease.

Overview

Lung abscess is a localised area of necrosis with suppuration in lung tissue. Two types: primary (in an otherwise normal lung, commonly from aspiration of infected material) and secondary (complicating another lung disease or arising from a distant site).

Etiopathogenesis

Common isolates: streptococci, staphylococci, various gram-negative organisms. Five routes of introduction:

Aspiration of infected material — food, decaying teeth, gastric contents, infected gingivae/teeth, necrotic oral/upper-respiratory/nasopharyngeal tissue; favoured by sleep, unconsciousness, anaesthesia, general debility, acute alcoholism.
Preceding bacterial infection — bronchopneumonia in a debilitated patient; occasionally TB, bronchiectasis, mycotic infection.
Bronchial obstruction — abscess forms distal to an obstructing tumour or impacted foreign body.
Septic embolism — infected emboli from pyaemia, thrombophlebitis, or vegetative bacterial endocarditis reach the right heart, lodge in the lung, and produce multiple abscesses.
Miscellaneous — infected pulmonary infarcts, amoebic abscess (Entamoeba histolytica), trauma, direct extension from a suppurative mediastinal/oesophageal/subphrenic/spinal focus.

Morphology

Distribution: aspiration abscesses favour the right lung (its main bronchus is more vertical) and are usually single, typically in the lower part of the right upper lobe or apex of the right lower lobe. Abscesses from preceding pneumonia or septic/pyaemic spread are often multiple, scattered throughout the lung.

Gross: size ranges from a few mm to 5–6 cm cavities, containing exudate. Acute abscesses are surrounded by acute pneumonia with a poorly-defined, ragged wall; with time, the wall becomes fibrous as the abscess chronifies.

Microscopy: destruction of lung parenchyma with suppurative exudate filling the cavity. Initially surrounded by acute inflammation; later replaced by chronic inflammatory infiltrate (lymphocytes, plasma cells, macrophages); chronic cases show substantial fibroblastic proliferation forming a fibrocollagenic wall.

Clinical Features

Fever, malaise, weight loss, cough, purulent expectoration, haemoptysis in about half. Clubbing in ~20%. Secondary amyloidosis can occur in chronic, longstanding cases — the same chronic-suppuration-driven mechanism seen in Bronchiectasis.

Clinical Relevance

The right-lung predominance of aspiration abscesses follows directly from a simple anatomic fact — the right main bronchus is more vertical and in line with the trachea — which is why the same anatomic logic explains right-sided predominance across multiple aspiration-related lung conditions, not just abscess.
The distinction between typically single (aspiration) and typically multiple (septic embolic) abscesses is a practical diagnostic clue — multiple abscesses scattered through the lung should prompt a search for a distant septic source (endocarditis, thrombophlebitis, pyaemia) rather than a primary aspiration event.
The abscess wall’s evolution from poorly-defined/ragged (acute) to fibrocollagenic (chronic) mirrors the same acute-to-chronic inflammatory transition seen generally in Chronic and Granulomatous Inflammation — recognising it as an instance of that general pattern, rather than a lung-abscess-specific process, ties this topic back to first-principles inflammation.
Secondary amyloidosis as a chronic complication reinforces a recurring theme across suppurative lung diseases (also seen in bronchiectasis) — sustained antigenic/inflammatory stimulation, regardless of the specific initiating disease, is the shared driver, so amyloidosis risk should be considered in any longstanding suppurative process, not just this one.