Collapsed lung, coloured X-ray. Collapsed left lung (right, atelectasis) as a result of the abnormal presence of gas (pneumoperitoneum). This gas is seen as a diaphragmatic cup-shaped prominence (cupula, lower right). Pneumoperitoneum may be caused by trauma, bowel obstruction or peptic perforation. It may also occur post- operatively following a general anaesthetic. Symptoms of atelectasis include a low-grade fever, chest pains and mild shortness of breath. Post- operative atelectasis is treated with deep breathing exercises and respiratory therapy, other forms require the diagnosis and treatment of the underlying cause.