Answers

Short answers

1 The chest radiograph shows near complete opacification of the right hemithorax, with preservation of lung volumes and absence of air bronchograms. These signs are in keeping with a large right pleural effusion with no mediastinal shift. The patient had no significant secondary scoliosis.

2 Ultrasound scan of the chest, blood culture, and a full blood count should all be performed. In addition, electrolytes, serum albumin, and C reactive protein concentrations should be measured.

3 This patient has a parapneumonic effusion/empyema (thick fluid with loculations/overt pus).

4 Streptococcus pneumoniae is the most common isolated cause for a parapneumonic effusion in developed countries.

5 The specific treatment a child currently receives is dependent on unit expertise and local practice. Approaches include:

Chest drain with or without fibrinolytics—the preferred initial approach for most paediatric centres in the United Kingdom

Mini-thoracotomy—preferred by only a few centres in the United Kingdom

Video assisted thoracoscopic surgery with drain insertion—available in a few centres in the United Kingdom

Open decortication—used as a late stage operation in most paediatric centres in the United Kingdom

Thoracocentesis—not recommended in children.

Long answers
1 Radiological abnormalities
The chest radiograph shows near complete opacification of the right hemithorax (indicated by arrow on fig 2), with preservation of lung volumes and absence of air bronchograms. These signs are in keeping with a large right pleural effusion with no mediastinal shift. The effusion appears loculated/"walled off"; for example, in the right lower zone the increased density is laterally located, obscuring the costophrenic angle and right hemi-diaphragm. The right heart border is visible, however, indicating that the effusion does not involve the cardio-mediastinal pleura.

View larger version (95K): [in this window] [in a new window] [PowerPoint Slide for Teaching]   Chest radiograph (posteroanterior view) showing near complete opacification of the right hemithorax (arrow)

• Chest radiograph
  
• Ultrasound scan of chest
  
• Blood culture
  
• Full blood count
  
• Electrolytes (to detect inappropriate antidiuretic hormone syndrome)
  
• Serum albumin
  
• C reactive protein (possibly a useful marker of progress of disease).
  

Ultrasound of the thorax can be used to quantify the size of a pleural effusion and also to differentiate a collapsed or consolidated lung from pleural fluid in the case of a complete "white out" on chest radiograph. Loculations and fibrin strands can also be detected by ultrasound. The principal role of ultrasound is to mark the site for a chest drain insertion.² There is no place for routine use of computed tomography in children with empyema.³ Computed tomography should instead be reserved for cases where complications such as a lung abscess are suspected or where ultrasound has been inconclusive.¹

Parapneumonic pleural effusions are dominated by polymorphonuclear leucocytes, but a predominance of lymphocytes in an exudate should raise the possibility of tuberculosis or malignancy. In present day practice, pleural fluid culture is often sterile because antibiotics have been used before obtaining a pleural fluid sample. In a multicentre study conducted in the United Kingdom, only 17% of cases of childhood empyema were culture positive.⁴ In studies using newer molecular techniques—for example, pneumococcal or broad range 16S polymerase chain reaction—an aetiological agent was detected in about 75% of culture negative cases.^{5 6}

3 Parapneumonic effusion and empyema
Parapneumonic effusion and empyema are causes of significant childhood morbidity. An estimated 0.6% of childhood pneumonias progress to empyema, which affects 3.3 individuals per 100 000 children.⁷ The incidence of childhood empyema has increased dramatically in children in the United Kingdom, Europe, and North America^{1 8}; however, an explanation for this phenomenon has yet to be determined. The principal differences between adult and paediatric pleural infections are that children rarely have an underlying lung disease and the final outcome is almost always excellent in children.¹

When associated with infection, pleural effusions are usually unilateral; bilateral empyemas are very rare. Bilateral effusions may indicate tuberculosis or a parasitic infection.⁹ Other infections (such as a lung abscess) and chronic suppurative conditions (such as bronchiectasis) can also produce pleural effusions.¹⁰ Predisposing factors for pleural effusions include immunodeficiencies, aspiration, post-surgery complications, and trauma. Of note, pleural effusions are not always secondary to infection and can be genuinely sterile. Rarely, an effusion is the presenting sign of an underlying malignancy in a child who was well before reporting the symptoms related to the effusion. Many of the other secondary causes of pleural effusion are related to underlying conditions such as congenital heart disease, renal disease, connective tissue disorders, and trauma (including cardiothoracic surgery).

Although pleural infection is a continuum, it has traditionally been divided into three stages¹¹:

• Exudative stage: clear fluid accumulates within the pleural cavity (simple parapneumonic effusion) as a result of the inflammatory process associated with the underlying pneumonia
  
• Fibropurulent stage: fibrin is deposited in the pleural space, leading to septation and the formation of loculations. White cells increase, causing the fluid to thicken (complicated parapneumonic effusion) and eventually become overt pus (empyema)
  
• Organisational stage: intrapleural membranes become thick and non-elastic as a result of fibroblasts infiltrating the pleural cavity.
  

In an attempt to help guide management, Hamm and Light determined the pleural fluid pH and lactate dehydrogenase concentration that define each stage.¹¹ In the exudative stage, the pH is normal and the lactate dehydrogenase concentration is less than 1000 IU. In the fibrinopurulent stage, the pH is less than 7.2 and the lactate dehydrogenase concentration is greater than 1000 IU. These values apply to adult patients, however, and have not been properly validated in the paediatric population. The British Thoracic Society guidelines stipulate that there is no place for routine biochemical analysis of pleural fluid in guiding therapy in children.¹

The child with a parapneumonic effusion and empyema usually presents with classic symptoms of pneumonia (cough, dyspnoea, fever, malaise, loss of appetite), although perhaps they are more unwell than other children who present with symptoms of pneumonia and have pleuritic chest pain. In those already diagnosed with pneumonia, a spiking fever and lack of improvement after 48 hours of antibiotic treatment can signal the presence of an effusion. A pleural effusion is suggested by unilateral signs of decreased chest expansion, stony dullness to percussion, and reduced or absent breath sounds. Measurement of oxygen saturation is particularly important, with levels below 92% indicating severe disease.¹² Examination should also include assessment of the child’s state of hydration, their height and weight, and the presence of scoliosis or any underlying disorders.

4 Pathogens responsible
In a previously well child, a pleural effusion is usually secondary to acute bacterial pneumonia and, less often, owing to a chronic infection such as pulmonary tuberculosis.¹³ Streptococcus pneumoniae has been found to be the principal pathogen in childhood empyema, with serotype 1 accounting for 24-50% of culture positive cases.^{14 15} Pneumonia caused by group A streptococcus and Staphylococcus aureus are more likely to progress to empyema.¹⁶

5 Treatment options
The aim of treatment for parapneumonic effusion and empyema is to stop sepsis and restore pleural fluid circulation, thus aiding restoration of normal lung function. In order to achieve this outcome, the pleural cavity needs to be sterilised and inflammatory debris and fluid removed; the lung then needs to be allowed to expand as much as possible. Symptomatic treatments include analgesia and antipyretics; intravenous antibiotics; oxygen if necessary (that is, in children who have blood oxygen saturation of less than 93%); and fluid therapy if the child is dehydrated or unable/unwilling to drink.

The specialised treatment a child receives is usually the result of local practice and expertise. Variation in practice is partly owing to the lack of randomised controlled trials of treatment for parapneumonic effusion and empyema.¹ In addition, children virtually always recover, irrespective of the treatment they receive.¹⁵ The specific treatment options are briefly discussed in table 1 (treatment options are discussed in detail in recent review by Sonnappa and Jaffe¹⁷).

Antibiotic selection should cover the most likely causative organisms and should take into account any predisposing condition and potential pathogen exposure. In particular, treatment decisions should take into account whether the pleural infection is secondary to a community or hospital acquired pneumonia, surgery, or trauma, and whether aspiration is likely to have occurred. The antibiotics commonly used to treat community acquired pneumonia are cefuroxime, co-amoxiclav, and clindamycin.¹ Many centres in the United Kingdom continue with intravenous antibiotics until the child is afebrile or at least until the chest drain is removed. Oral antibiotics such as co-amoxiclav are then given at discharge for 2-4 weeks, but longer in cases with residual disease.

Many small parapneumonic effusions will respond to antibiotics without the need for further intervention. Effusions that are enlarging and/or compromise respiratory function in a pyrexial unwell child do need drainage. Rigid large bore drains should be inserted by paediatric surgeons or thoracic surgeons. Pigtail or small bore soft drains (inserted by the Seldinger technique) can be used by respiratory paediatricians or interventional radiologists. Intrapleural fibrinolytics shorten hospital stay and are recommended for any complicated parapneumonic effusion or empyema.⁴ Failure of chest tube drainage, antibiotics, and fibrinolytics should prompt early discussion with a thoracic surgeon.

Children should be followed-up after discharge until they have recovered completely and their chest radiograph has returned to near normal. The majority of affected children are previously healthy individuals; follow-up investigations are, therefore, unnecessary. The prognosis in children with empyema is usually very good. Follow-up studies have shown that, despite the heterogeneity of treatment approaches, the majority of children make a complete recovery and their lung function returns to normal.¹

Patient outcome
A chest drain was inserted on admission and the patient received six intrapleural doses of urokinase on days 1-3. His tachypnoea and respiratory distress had resolved by day 4-5, and he was afebrile by day 5-6. He was treated with intravenous augmentin for 7 days and received oral augmentin for a further 3 weeks. On day 7 of admission the patient was discharged from hospital. By 8 weeks he had made complete clinical and radiological recovery.

Cite this as: BMJ 2009;339:b2150