There are several similar cases described in the literature where the patient was first given the diagnosis pericarditis and subsequently pneumothorax after a review of the X-ray pictures (4) – (8). Pneumothorax is an accumulation of air in the space between visceral and parietal pleura. Pneumothorax is called spontaneous if no triggering events can be identified. Studies from both Norway and the USA have shown that the condition is far more prevalent in men than in women (9, 10). Spontaneous pneumothorax normally arises as a result of an apical, subpleural emphysema bladder bursting. Smokers are at greater risk, and persons with spontaneous pneumothorax have a tendency to be taller than control patients (11, 12).
Noisy pneumothorax has been described several times in the literature in the form of case histories (4) – (8). One material reports that less than 1 % of the spontaneous pneumothorax cases are noisy pneumothorax, another up to one of six cases (5, 6).
The sound that is heard with noisy pneumothorax is described in the literature as scraping, bubbling, clicking or crunching. This sound is also called Hamman’s sign, and was initially described by Louis Hamman in 1937 in connection with pneumomediastinum (13). Pneumomediastinum is air in the mediastinum and can develop spontaneously, following an injury or in connection with a change in intrathoracic pressure as in an asthma attack, vomiting or a visit to a dentist where compressed air is used (14). In cases of adventitious sounds over the precordium, it is particularly important to consider the possibility of air in the mediastinum. In some cases of pneumomediastinum, subcutaneous emphysema is also found.
The friction rub sound with noisy pneumothorax occurs when the heart’s mechanical work causes movement of small quantities of air intrapleurally (7). The sound occurs most frequently with left-sided, small apical air caps and is most clearly audible in left lateral decubitus position. Only one case of right-side pneumothorax with such adventitious sounds has been described (6). Phonographic studies have shown that there are often several adventitious sounds, both systolic and diastolic, and that they can vary with the respiratory cycle and body position (15).
Normal vertical chest X-rays with posterior-anterior radiation is normally enough to make the diagnosis pneumothorax. X-rays taken during expiration are not recommended as part of an ordinary routine assessment (12). Small air caps can be difficult to detect, and it is easy to overlook a small pneumothorax, particularly if one is not actively looking for it. On vertical images, an apical, hyperclear zone is usually seen with a visible contour of visceral pleura and absent vascular markings peripherally. On decubitus images it may be more difficult to diagnose a pneumothorax since air rises up to the highest point and then collects anteriomedially against the base of the lung (16).
A pneumothorax can be treated in different ways, depending on the cause, symptoms, size of the air cap and whether it is a recurring condition. There are no special guidelines for treating noisy pneumothorax. The British Thoracic Society has drawn up general guidelines for treating spontaneous pneumothorax (12). According to these guidelines, patients with small air caps can be monitored as outpatients, while recurring air caps should be treated with aspiration, oxygen, drains or pleurodesis, depending on the size, number of recurrences and symptoms.
Having had spontaneous pneumothorax can have consequences for choice of occupation and leisure activities. These patients should be protected from barotrauma (rapid changes in air pressure). Previous spontaneous pneumothorax is a contraindication for diving with compressed air tanks if it has not been treated with bilateral pleurectomy (17). The danger lies in the fact that air expands when the pressure drops as the diver rises to the surface. Patients who have had pneumothorax should also be careful about air travel (18). The air pressure in the cabin is lower than the pressure on the ground, and this can cause a pneumothorax to expand. The expansion of air at lower pressures can also make the patient disposed to develop tension pneumothorax, which is a medical emergency situation. A tension pneumothorax develops when a one-way valve forms that allows air into the pleural cavity but not out again. The British guidelines recommend chest X-rays to confirm full reversal of pneumothorax before air travel, and waiting about a further seven days after normalisation (18).
In our patient, the air travel itself may have contributed to both the recurrence of the pain and to the diagnosis. The low barometric pressure in the cabin may have caused the air cap to expand during the flight.
It is easy to be wise after the event. Noting that the friction rub was synchronous with respiration or pulse might have helped to some extent with the diagnosis. Whereas friction rub caused by pericarditis or noisy pneumothorax will be synchronous with the heart rhythm, the adventitous sound associated with pleuritis, for example, stops if the patient holds his or her breath. It is of course regrettable that the air cap apically on the chest X-ray during expiration was not detected on the first review of the X-rays. On the other hand, this has been a reminder to us of how important it is to keep updated with respect to more uncommon diagnoses. In our case the patient’s condition could have taken a serious turn in connection with the flight, many hours long, that he took after discharge from our department. A correct diagnosis initially would have prevented this.