Empyema

For medical students2 min readUpdated 2026-10-10

Empyema is an accumulation of pus within naturally occurring anatomical body cavities or the lumina of hollow organs, representing a specific form of purulent inflammation. The process is accompanied by impaired drainage of contents and progressive suppression of local protective barriers.

Type of inflammationExclusively purulent inflammation (not serous, fibrinous, or hemorrhagic)

Common locationsPleural cavity, gallbladder, appendix, fallopian tubes

Primary causeDirect spread of a purulent process from adjacent affected organs (e.g., lung abscess)

OutcomeObliteration (complete scarring and closure) of the organ lumen during prolonged inflammation

Pathological Process and Etiology

In pathology courses, empyema (empyema) is defined as a specific form of exudative inflammation. It is important to emphasize that by its nature, this is exclusively purulent inflammation — differing fundamentally from serous, fibrinous, or hemorrhagic variants. The main anatomical feature of this pathological process is that the accumulation of purulent exudate occurs within natural body cavities or the lumina of hollow organs.

Etiological analysis shows that the condition most frequently develops secondarily. The primary cause is the direct spread of infection from pre-existing purulent foci located in adjacent organs. A classic textbook example of such spread is the development of pleural empyema, which occurs as a direct consequence and complication of a lung abscess.

Features of Hollow Organ Involvement

Of particular interest to pathomorphologists is the development of purulent inflammation in tubular structures or organs with narrow excretory ducts. Classic examples of such anatomical structures include the gallbladder, appendix, and fallopian tubes.

In these structures, the pathogenesis of the disease is inextricably linked to drainage. The critical event triggering severe damage is impaired pus drainage. Once the natural passage of contents is blocked, ideal conditions are created within the closed space for the progression of purulent inflammation and the total destruction of tissue barriers.

Pathogenesis: Cascade of Local Defense Failure

Drainage blockage triggers a destructive cascade that leads to a profound disruption of the organ's local defense mechanisms. This pathogenetic process can be divided into several sequential stages:

Cessation of content renewal. Under physiological conditions, secretions are continuously replaced; however, during stasis, this vital function is lost.
Circulatory impairment. The continuous accumulation of purulent mass leads to a rapid increase in intraluminal pressure. Mechanical overstretching of tissues inevitably causes compression of the vascular bed, leading to marked circulatory disturbances in the wall of the affected organ.
Decreased secretion of protective substances. Progressive ischemia triggers a sharp drop in the synthesis and secretion of specific protective substances. In particular, the production of secretory immunoglobulins (Ig) plummets, ultimately depriving the mucosa of its ability to resist aggressive factors.

Morphological Outcomes

The prognosis and final morphological picture of the disease depend directly on the duration of the pathological process. In prolonged purulent inflammation under conditions of impaired drainage, irreversible structural remodeling occurs.

Regular and most frequent outcome of the chronic form is obliteration. This process represents the complete scarring and closure of the lumen of the affected hollow organ, leading to the total loss of its original anatomical configuration and complete exclusion from normal physiological functioning.

Mnemonic

Remember the triad of hollow organ empyema pathogenesis via the "Three S" rule: Stop renewal (no drainage) → Squeeze vessels (pressure rise) → Sink defense (drop in secretory Ig).

Frequently asked questions

How does empyema differ from phlegmon?

Empyema and phlegmon differ in their localization and the boundaries of the purulent inflammation.

Feature	Empyema	Phlegmon
Definition	Purulent inflammation of pre-existing body cavities or hollow organs	Spreading (diffuse) purulent inflammation infiltrating and dissecting tissues
Focus boundaries	Confined to the anatomical cavity	Ill-defined, diffuse, lacking clear demarcation

Which microorganisms most commonly cause pleural empyema?

Pleural empyema is most frequently caused by bacterial pathogens, as well as anaerobic flora.

Pneumococcus (Streptococcus pneumoniae) — a frequent causative agent of parapneumonic processes.
Staphylococcus (Staphylococcus) — causes staphylococcal purulent pleuritis.
Streptococcus (Streptococcus) — causes streptococcal purulent pleuritis.
Anaerobes — characteristic of lung abscess and empyema.
Mycobacterium tuberculosis (Mycobacterium tuberculosis) — causes tuberculous empyema.

Classifications also distinguish diplococcal and mixed infection forms.

What macroscopic features characterize gallbladder empyema?

Macroscopically, gallbladder empyema manifests with signs of purulent inflammation and accumulation of exudate within a closed cavity.

Gallbladder wall — thickened and edematous, with petechial hemorrhages.
Lumen — filled with purulent exudate, occurring when the cystic duct is obstructed.
Organ shape — appears as an enlarged, sac-like formation.
Consistency — palpates as firm or elastic.

What systemic complications can develop in prolonged empyema?

Systemic complications of prolonged empyema as an isolated condition are not explicitly listed in the source materials.

What is the fundamental difference between empyema and an abscess?

Empyema is purulent inflammation within pre-existing natural body cavities or the lumina of hollow organs. In contrast, an abscess (such as a lung abscess, which can lead to empyema) forms directly within the solid parenchyma of an organ tissue.

Which organs are most susceptible to empyema when drainage is obstructed?

According to classic pathomorphological data, this process typically affects hollow organs with narrow lumina: the gallbladder, appendix, and fallopian tubes.

Why does local immune defense decrease in empyema?

Impaired drainage increases intraluminal pressure, leading to vessel compression and circulatory disturbances in the organ wall. Ischemia causes decreased synthesis and secretion of protective substances, including secretory immunoglobulins (Ig).

What morphological outcome results from prolonged empyema?

With prolonged purulent inflammation, the typical outcome is obliteration — the complete scarring and closure of the lumen of the affected hollow organ.

Go deeper

Morphological differences between purulent inflammation and serous, fibrinous, and hemorrhagic inflammation.
Pathogenesis of lung abscess formation as a primary source of infection.
Mechanisms of microcirculatory disruption during elevated intraluminal pressure.
The role of secretory immunoglobulins (Ig) in the local defense of mucous membranes.
Histological picture of hollow organ obliteration.