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A 48-year-old woman with no significant medical history was admitted following a road traffic accident. She developed right-sided pleuritic chest pain, a dry cough and severe breathlessness. On physical examination, the patient had a pulse rate of 90 beats/min, blood pressure of 130/80 mmHg and a respiratory rate of 30 breaths/min. There was crepitus on the right chest wall and breath sounds were markedly diminished on that side. She also had severe tenderness in the region of her left shoulder. Cardiovascular, abdominal and neurological examination did not reveal any abnormality.
A chest X-ray on admission revealed rib fractures from the second to the sixth ribs, subcutaneous emphysema and a pneumothorax on the right side (figure 1). She had also sustained a fracture of the neck of the left humerus. Baseline blood investigations showed a haemoglobin of 11.6 g/dl, white blood count of 12.6 × 106/l. Arterial blood gas analysis revealed moderate hypoxaemia. An intercostal tube drainage was instituted in the right thoracic cavity. Her subsequent chest X-ray revealed a cystic lesion in the right lower lobe following complete expansion of the right lung (figure2).
- What is the differential diagnosis?
- What is the most probable diagnosis?
- What is the treatment of this condition?
The various aetiologies to be considered following trauma are pulmonary haematoma, contusion, traumatic lung cyst, loculated haemopneumothorax.1 Also to be considered in the differential diagnosis are pre-existing conditions in an adult like lung abscess, tuberculous and mycotic cavities, hydatid cysts, cavitating bronchogenic carcinomas and, in children, congenital pulmonary cyst, post-pneumonic pneumatocoele and sequestration.
The most probable diagnosis is traumatic lung cyst.
“Clinical course of traumatic lung cysts is usually uncomplicated”.1 Complete resolution occurs in 2–16 weeks requiring only close observation and symptomatic treatment. Prophylactic antibiotic treatment is not required, despite transient fever and leucocytosis. Secondary infection of traumatic lung cyst with abscess formation is uncommon. Very rarely it may fail to regress and may enlarge resulting in respiratory distress or pneumothorax.
When the patient was seen a month later following discharge, the cystic lesion had completely disappeared (figure 3).
Lung laceration due to trauma may result in pneumothorax, haemothorax, contusion, traumatic pseudocyst and massive haemoptysis.2 Blunt chest trauma causes contusion while penetrating injury gives rise to haematoma. Recognition of traumatic lung cysts is important to avoid confusion with other causes of lung masses or cavities as it resolves spontaneously requiring no special treatment.
Closed chest trauma may result in the development of one or more cystic spaces within the lung that may remain airfilled or may partly fill. The trauma is usually blunt. Children and young adults seem to be more prone because of greater flexibility of their thoracic walls. In a recent review of 40 cases of traumatic lung cyst, 88% occurred in patients under 32 years of age. Three mechanisms have been suggested to explain their development1 3:
sudden compression of an area of the lung closes off a segment of peripheral bronchial tree and creates within it a bursting, explosive, pressure that is expended in the rupture of successive alveolar walls within the lobules supplied by the occluded bronchus
compression of the elastic chest wall while the glottis is closed may result in rupture of the small bronchi and pulmonary parenchymal disruption with cavitation because air from the compressed part of the lung cannot escape quickly enough
a concussion wave produced by the blow to the chest generates shearing stress that tears the lung parenchyma and causes traumatic cavities.
The cyst may contain air or blood derived from the torn alveolar capillaries. The cyst wall is thin and is made up of fibrous tissue and surrounding compressed alveolar tissue. Rarely, there may be colonisation of a post-traumatic lung cyst by an asymptomatic aspergilloma.4
Traumatic lung cysts
may occur following blunt chest trauma
usually appear within 12–24 hours of injury
may be single or multilocular, ranging from 2–14 cm
spontaneous regression occurs in 2–6 weeks
it is important to recognise such lesions to avoid confusion with other causes of lung masses or cavities
Symptoms include haemoptysis, chest pain, cough, dyspnoea and low grade fever. Haemoptysis is present in 50% of cases and may last for several days. Low grade fever and leucocytosis lasting for one to two weeks reflect reparative process of the injured lung.
The findings on chest X-ray depend on timing after the injury, associated pulmonary parenchymal injuries (contusion/haematoma), and whether the cyst is filled with air and/or blood.1-3 5The cyst may be single or multiple, unilocular or multilocular ranging from 2–14 cm, located subpleurally and usually appears 12–24 hours after injury. Occasionally there may be a delayed appearance 3–6 days after the resolution of the surrounding lung contusion. In comparison, lung contusions usually appear within one hour, resolve in 48–72 hours, and disappear in 7–10 days.
Spontaneous regression occurs in 2–6 weeks although the cyst may occasionally persist for up to 4 months. Surgical resection is not necessary provided there is definite evidence of decreasing size of the lesion by 6 weeks following injury in adults and by 3 months in children. Surgery is indicated if there is an infective complication unresponsive to antibiotic treatment or if other cavitatory lesions of the lung are to be excluded.
Traumatic lung cyst.