Empyema Necessitans

Empyema necessitans is a pleural empyema that has eroded through the parietal pleura and chest wall to form a subcutaneous collection or abscess, sometimes with a discharging sinus. The pus tracks along the line of least resistance, in the anterior or lateral chest wall, and sometimes into the mediastinum or abdomen.

It is rare, and linked with indolent organisms and delayed diagnosis. The classical causes are Mycobacterium tuberculosis (the commonest, particularly in endemic regions), Actinomyces and Nocardia. Other causes include Staphylococcus aureus, streptococci, Aspergillus, Blastomyces, Coccidioides and anaerobes. Risk factors include HIV, diabetes, alcohol use, malnutrition, immunosuppression and untreated or inadequately drained empyema.

Pathophysiology. Persistent infected pleural fluid under pressure causes necrosis of the parietal pleura and intercostal muscle, tracking into the subcutaneous tissue. Chronic inflammation leads to a thick pleural peel and rib erosion, and in actinomycosis, to multiple sinuses and sulphur granules.

A tender, fluctuant, pulsatile chest wall swelling (often over the 2nd to 5th intercostal space anteriorly or laterally, which may expand with cough), with fever, night sweats, weight loss, cough and pleuritic pain over weeks to months. Skin erythema, a discharging sinus and rib tenderness are seen. Reduced breath sounds and dullness indicate the underlying empyema.

Spread to the mediastinum, spinal canal or pericardium, sepsis or respiratory failure needs urgent assessment.

• Clinical diagnosis of a chest wall mass with empyema, and imaging to confirm.
• CT chest with contrast: loculated pleural collection with enhancing pleural thickening (split pleura sign), a track through the chest wall into a soft tissue collection, rib erosion or periostitis, and parenchymal disease or lymph nodes.
• Ultrasound shows a chest wall collection and guides sampling.
• Aspiration of the collection or pleural fluid: Gram stain, culture (aerobic and anaerobic), acid fast stain, mycobacterial culture and nucleic acid test, fungal culture, and histology of tissue. Sulphur granules suggest actinomycosis, and branching filaments on modified acid fast stain suggest Nocardia.
• Blood tests: full blood count, C-reactive protein, HIV testing, glucose and albumin. Blood cultures.
• Biopsy to exclude malignancy if there is a mass.

Differential diagnosis.

• Chest wall abscess or tuberculous cold abscess without pleural disease
• Chest wall tumour (sarcoma, lymphoma, metastasis)
• Rib osteomyelitis
• Pleurocutaneous fistula
• Lung cancer with chest wall invasion
• Hydatid cyst

• Drainage of the empyema with a chest drain (14 to 28 French, image directed) and drainage of the chest wall collection, with irrigation. Intrapleural alteplase 10 mg with dornase alfa 5 mg twice daily for 3 days helps loculated collections.
• Antibiotics directed by the organism and given for a prolonged course.
• Tuberculosis: rifampicin 10 mg/kg (maximum 600 mg), isoniazid 5 mg/kg (maximum 300 mg), pyrazinamide 25 mg/kg and ethambutol 15 mg/kg daily for 2 months, then rifampicin and isoniazid for 4 months (9 to 12 months for extensive disease), with pyridoxine 10 to 25 mg daily.
• Actinomycosis: benzylpenicillin 18 to 24 million units daily intravenously for 2 to 6 weeks, then amoxicillin 1 g three times daily for 6 to 12 months. Doxycycline 100 mg twice daily is an alternative in penicillin allergy.
• Nocardiosis: co-trimoxazole (trimethoprim 5 to 10 mg/kg daily in divided doses) with imipenem or amikacin in severe disease, for 6 to 12 months.
• Staphylococcus aureus: flucloxacillin 2 g intravenously every 6 hours (vancomycin 15 to 20 mg/kg every 8 to 12 hours for meticillin resistant strains). Anaerobic and mixed infection: amoxicillin-clavulanate 1.2 g intravenously three times daily or piperacillin-tazobactam 4.5 g every 6 to 8 hours.
• Fungal infection: amphotericin B or itraconazole 200 mg twice daily, directed by the organism.
• Surgery: decortication, debridement of necrotic chest wall tissue and bone, and open window drainage with flap closure when drainage and medical therapy fail or for chronic cavity.
• Nutrition, glycaemic control, HIV treatment and smoking cessation.

Complications and prognosis. Rib osteomyelitis, mediastinitis, chronic sinus tract, empyema recurrence, and lung entrapment. The outcome is good with prolonged therapy and adequate drainage, and poor with delay or immunosuppression.

Monitoring. Review of drain output and imaging every 3 to 7 days initially, then monthly CT or radiograph, inflammatory markers, and drug toxicity monitoring (liver function monthly for antituberculosis therapy).

Referral and escalation. Refer to thoracic surgery, infectious diseases or a tuberculosis clinic, and to intensive care for sepsis.