Article Text

Infected lung cysts
  1. Darryl A Chung
  1. Thoracic Surgical Unit, Norfolk & Norwich Hospital, Brunswick Road, Norwich NR1 3SR, UK

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    A previously well 31-year-old woman was referred to the thoracic surgical unit following 11 days of unsuccessful antibiotic treatment (amoxycillin then ceftazidime) for ‘flu-like’ illness associated with an unproductive cough and radiographically evident cystic lesions in the left lung (figure 1 and 2). Apart from a vague recollection of ‘air bubbles’ in her lungs in early childhood that was never followed up, she had no medical history of note, and no family history of emphysema. She had previously smoked an average of 15 cigarettes daily for 15 years but had stopped a year earlier.

    Figure 1

    Postero-anterior erect chest X-ray showing left lung cysts

    Figure 2

    Lateral view of lung cysts

    Examination revealed a pyrexia of 38.1°C, a regular pulse rhythm at 100 beats/min and reduced air entry in the left upper and mid zones of the chest, but no other abnormalities. Her haemoglobin level was 11.4 g/dl and white cell count 17.1 × 109/l. A diagnostic percutaneous aspiration was performed, yielding purulent fluid which gave a sterile culture, and no acid-fast bacilli. Aside from a swinging low-grade pyrexia, the signs of sepsis settled on a course of clindamycin and metronidazole at which time the patient had a left thoracotomy for excision of cystic lesions in the apical segment of the lower lobe. The lesions appeared to have no air leak or communication with the airways. Histology showed lung abscess with necrotic and haemorrhagic material and chronic inflammation.

    Questions

    1
    Are these lung cysts congenital or acquired?
    2
    What infective organisms may produce such a picture?
    3
    What are the indications for surgical intervention?

    Answers

    QUESTION 1

    On radiological grounds alone it is impossible to determine the origins of these cysts, in the absence of previous X-rays. Although the history of childhood lung cysts is vague, it is probable that these are congenital, but multiplicity is not characteristic, although not uncommon. The thin-walled appearance of these cysts also suggests a congenital cause.

    QUESTION 2

    The organisms most commonly found in infected lung cysts are listed in box FB1.

    Figure FB1

    QUESTION 3

    Indications for surgical intervention of lung cysts are given in box FB2.1

    Figure FB2

    Discussion

    The radiographs show multiple cystic lesions with air-fluid levels. Congenital parenchymal lung cysts are usually thin-walled, unilocular and singular, usually involving one side and more frequently involving the lower lobe.2 Multiplicity or multilocularity suggests an acquired cause, most commonly infection, whether primary or secondary. Cystic fibrosis also gives rise to multiple cysts. Infective destruction of the epithelial lining often makes it difficult (or impossible) to determine the true origins of the cysts on histopathological grounds.

    Infected intrapulmonary collections most commonly present with cough with purulent sputum, fever, dyspnoea and chest pain. Examination may reveal tachypnoea, tracheal shift, dullness to percussion, rhonchi, decreased breath sounds and tachycardia.

    Primary suppurative organisms classically produce acute abscess formation in previously healthy lung tissue, although pre-existing lung pathology is common. They produce extensive rapid tissue necrosis. Cavitation due to post-primary pulmonary tuberculosis, however, is usually insidious. More commonly, secondary suppuration occurs in lung injured by aspiration of vomitus during decreased consciousness (head injury, general anaesthesia, inebriation, stroke, epilepsy, drug overdose), the organisms being predominantly anaerobes.3Secondary infection also occurs following lobar collapse or pulmonary infarction, and in immunocompromised states, such as acquired immunodeficiency syndrome, lymphoma, steroid therapy, diabetes mellitus, alcoholism, severe comorbid illness, and immunosuppression therapy (organ transplant recipients, cancer chemotherapy). Hospital-acquired infections occur particularly in the ventilated intensive care patient. Staphylococcal or streptococcal septicaemia, as well as transdiaphragmatic bacterial translocation from a subphrenic collection, can also result in secondary pulmonary suppuration. The absence of accompanying consolidation or collapse in this patient, however, makes secondary pneumonic processes unlikely. The negative culture from the aspirate is not surprising in the face of prior antibiotic therapy.

    Most lung abscesses resolve on appropriate antibiotic therapy and postural drainage. However, in about 20%, persisting disease requires surgical intervention. Although chest tube drainage of infected lung collections has been advocated,4 there is the real possibility of an empyema developing. The treatment is ultimately resection (cystectomy, segmentectomy or lobectomy; very rarely pneumonectomy), for such large cysts, whether congenital or acquired.1 5

    Final diagnosis

    In the light of the history, albeit vague, of childhood lung cysts and the pathology being isolated to one segment of one lung, it is believed that these were congenital cysts that became secondarily infected.

    References

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