Empyema overview

Empyema Microchapters
Patient Information
Overview
Classification Subdural empyema Pleural empyema
Differential Diagnosis

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Prince Tano Djan, BSc, MBChB [2]

Overview

An empyema is a collection of pus within a pre-existing body cavity. It must be differentiated from an abscess, which is a collection of necrotic and suppurated tissue located in the parenchyma of an organ. Empyema is most commonly used to refer to pus collection in the pleural cavity although several other organs can be affected example brain, gallbladder, joint and urinary bladder. Thoracic empyema arises from an infection within the lung, often associated with parapneumonic effusions. Parapneumonic effusions may be uncomplicated or complicated effusions. Complicated parapneumonic effusion results when bacteria invade the pleural space with a resultant formation of an empyema.

Historical Perspective

Pleural infection was first described by Hippocrates as far back as 460-370 B.C. During this time open chest drainage was the sole treatment modality and was associated with high mortality. In 1873, Playfair gave the first description of a water-seal chest drainage system in the treatment of a child with thoracic empyema. In 1875, Gotthard Bülau a German Internist described the use of closed water-seal chest drainage to treat an empyema, as an alternative to the standard rib resection and open tube drainage. He punctured the pleura membrane with trocar and introduced a rubber catheter into the pleural cavity. The free end of the catheter inserted in a bottle one-third full of solution allowing pus to flow freely from the chest into the bottle. Closed chest tube drainage was experimentally practised during the influenza epidemic in 1917–19 when open surgical drainage was associated with a high mortality rate. This coincided with world war I and the resultant crisis of streptococcal pneumonia and empyema. Closed chest tube drainage became the standard of treatment from late 1950.

Classification

Empyema may be classified according to the etiology, anatomical location, and pathological course of the disease. Primary thoracic empyema occurs most commonly as iatrogenic empyema without associated pneumonia whereas secondary empyema happens more commonly secondary to pneumonia. Empyema necessitans is a spontaneous discharge of an empyema that has burrowed through the parietal pleura into the chest wall to form a subcutaneous abscess that may eventually rupture through the skin. On the basis of anatomical location, empyema may be classified depending on the affected organ for example; gallbladder empyema, subdural empyema, joint empyema and empyema cystitis. Empyema is mostly caused by bacteria. It may be tuberculous or nontuberculous. Tuberculous empyema is the most common cause of empyema necessitans with majority of affected patients being immunocompromised. There are 3 stages of empyema which are important in terms of the laboratory findings. These are exudative, fibrinopurulent and organizing.

Pathophysiology

The process leading to the formation of empyema involves migration of organisms into the pleural cavity. Lung parenchymal infection stimulates local pleural immune activation, neutrophil migration and release of inflammatory cellular components and toxic oxygen species, such as IL-6, IL-8 and tumour necrosis factor (TNF)-α. These mediators promotes endothelial injury resulting in increased pleural membrane permeability and increased osmotic pressure. With persistent inflammation, increased permeability of vascular and mesothelial membranes results in increased plasma leakage into the pleural cavity. Coagulation cascade when activated within the pleural cavity contributes to the development of a “fibrinopurulent” or “complicated” parapneumonic effusion. Fibrin is deposited over the pleural surfaces with fibrinous septae producing loculated effusions.

Causes

Streptococcus pneumoniae was the most common bacteria found in empyemas before the development of antibiotics. More recently, however, anaerobes have become the predominant organism in culture positive empyemas (and therefore careful anaerobic cultures should always be sent when working up parapneumonic effusions). Mixed aerobic and anaerobic infections are also common. In general any bacteria can cause an empyema, however different bacteria are associated with different rates of empyema formation. Some of the common bacteria causes include; bacteroides, fusobacterium, haemophilus influenzae, pneumococcal infections, staphylococcus aureus, streptococcus, and TB.

Differentiating Empyema overview from Other Diseases

Empyema must be diffrentiated from pneumonia, lung abscess, lung cancer and parapneumonic effusions on the basis of the presentation, physical examination findings, chest xray, ultrasound and CT scan findings. For instance on ultrasound, empyema is positive for suspended microbubble sign, air fluid level, curtains sign and loss of gliding sign but these are negative in a lung abscess.

Again empyema is differentiated from a lung abscess in that empyema on CT scan is seen as a lung mass whose cavity is regular with smooth well-defined boundary and shape changes with change in patient's position. Mass may resolve on antibiotics. The split pleura sign is present (most reliable sign to differentiate empyema from lung abscess).

Epidemiology and Demographics

The incidence and prevalence of empyema has been increasing over the past 15 years. More than 40% of patients have preexisting comorbidities. There have been a 26% increase in age and sex-standardized incidence rate from 8.7 per 100,000 person-years in 1997 to 11.8 per 100,000 person in 2011. This increment is most notably among older people aged ≥ 80 years (87.3% [from 20.4 per 100,000 in 1997 to 38.2 per 100,000 in 2011]) compared with people aged 40 to 64 years (27.8% [from 10.7 per 100,000 in 1997 to 12.6 per 100,000 in 2011]). Men are more commonly affected with empyema than women. The male to female ratio is approximately 1.7- to 3.1-fold higher in men than in women. The rate of patients with empyema requiring hospitalization appear to be increasing in western populations, however updated population-based data are scanty. The few available data on adult empyema have reported increase between 30% and 97% over the past 15 years in the United States and Canada. There is however a decreasing trend in the median days of hospital stay from 22 days 17 days.