Tuberculous thoracic empyema with empyema necessitans

Clinical History

The patient presented with complaints of pain in the right upper abdomen for 15 days along with fever and mild cough for the past 3 days. She had no history of jaundice. She had a past history of pulmonary tuberculosis for which she completed treatment 2 years before.

Imaging Findings

Ultrasound of abdomen showed an ill-defined thick echogenic-walled lesion along the diaphragmatic surface of the liver with probable extension into the right subpleural space. The lesion had mixed hypo and hyperechoic areas within. The possibility of liver abscess / hydatid cyst rupturing into the pleural cavity was considered. Further plain and post-contrast enhanced MDCT scan of the abdomen and pelvis was performed after intravenous and oral administration of contrast medium. The findings included:
- A well-defined biconvex-shaped thick hyperdense-walled pleural collection in the lower right chest with multiple calcific non-enhancing foci seen within the lesion. This collection extended into the sub-capsular surface of the liver in segment VII. This lesion had a lobulated contour and thin internal enhancing septae. The lesion showed mild wall enhancement without any internal enhancement.
- Involvement of the right lateral chest wall in the 9th intercostal space with collection extending into the intercostal space suggesting empyema necessitans. No osteomyelitis of ribs was seen.

Discussion

A. Background: Thoracic empyema is characterized by purulent content in the pleural space. It is commonly seen in bacterial pneumonia where there is transformation of synpneumonic effusion into empyema [1].
B. Clinical perspective: Clinical symptoms are those of pulmonary infection like fever and cough. Thoracic empyema may often present with pleuritic chest pain, whereas empyema necessitans may present with localised swelling in the chest wall.
C. Imaging Perspective: On imaging, empyema shows enhancement of thickened inner visceral and outer parietal pleura which are separated by the collection. This is called as split pleura sign. It shows obtuse margin with lung parenchyma which is compressed as opposed to lung abscess which shows acute angle. Also empyema shows lenticular shape and has smooth margins. Other CT findings of lung abscess include thick, irregular walls with bronchi and vessels abruptly terminating at the abscess wall with their distortion [2].
Tuberculous thoracic empyema is also seen as a complication of pleural tuberculous disease. Pleural tuberculosis occurs due to rupture of subpleural focus into pleural cavity or due to haematogenous dissemination [3]. This pleural fluid contains tubercular bacilli which may be difficult to culture. CT findings include pleural thickening and calcification associated with pleural collection and with or without extrapleural fat proliferation.
Empyema necessitans is characterised by collection in extrathoracic soft tissues due to decompression of thoracic empyema through the parietal pleura and weakness in the chest wall [4]. This occurs in setting of necrotising pneumonia or lung abscess and is seen commonly with Actinomyces and Mycobacterium tuberculosis. Thoracoplasty has been implicated in development of empyema necessitans as it induces weakness in the chest wall, favouring a disruption of the intrathoracic empyema through soft tissues and thus leading to the formation of an extrathoracic collection. Diagnosis is done by aspiration of the collection, cytology and culture for tuberculosis.
D. Outcome: Treatment is prompt evacuation of infected collection and antibiotics/anti-tuberculous therapy to prevent development of fibrothorax. Fibrothorax is characterised by diffuse pleural thickening/calcification but without effusion and suggests inactivity. Occasionally cholesterol from degenerated cells may accumulate in pleural collection resulting in chylous or pseudochylous empyema. This is seen as fat-fluid level or fat-calcium level on CT scan.
E. Take home message: Presence of 'split pleura sign' on CT scan indicates empyema; differentiating it from lung abscess. Thoracic empyema may extend into upper abdomen indenting the liver and also through intercostal space into subcutaneous tissues forming empyema necessitans.

Differential Diagnosis List

Final Diagnosis

Tuberculous thoracic empyema with empyema necessitans

URL:	https://www.eurorad.org/case/13537
DOI:	10.1594/EURORAD/CASE.13537
ISSN:	1563-4086