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The “hidden” pneumothorax
  1. M K Harkness,
  2. A Hashim,
  3. D Spence
  1. Department of Medicine, Friarage Hospital, Northallerton, North Yorkshire, UK
  1. Correspondence to:
 Dr M Harkness
 Department of Medicine, Friarage Hospital, Northallerton, North Yorkshire DL6 1JG, UK; mharknessdoctors.org.uk

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A 61 year old female smoker with a background of chronic obstructive airways disease (COPD, FEV1 1.2/FVC 1.85: predicted 2.42/2.86), pulmonary tuberculosis, carcinoma of the breast, and coeliac disease was admitted with a six day history of progressive breathlessness associated with a productive cough. Chest auscultation showed bilateral expiratory wheeze. Admission chest radiograph showed hyperinflated lungs. She was treated for an infective exacerbation of COPD.

Five days later she became acutely unwell. Auscultation of the chest showed severely reduced air entry on the right side; the trachea was central. Urgent portable erect and supine chest radiographs did not confirm a pneumothorax. Observations: sinus tachycardia at 140 beat/min with no acute changes on 12 lead electrocardiogram, respiratory rate of 40 breath/min, decrease in systolic blood pressure to 90 mm Hg, and oxygen saturation below 90%. An intercostal drain was inserted immediately because of the very high index of clinical suspicion and it was felt that definitive treatment was required. This produced subjective and objective improvement with an improvement in oxygen saturation and blood pressure, settling of pulse and respiratory rate, and an increase in air entry on the right side. Subsequent chest radiography showed the tube to be satisfactorily placed and there was no evidence of pneumothorax. The drain was removed two days later when bubbling had ceased, again with no radiological evidence of a pneumothorax. The day after the removal of the drain the patient felt increasingly breathless, in the absence of objective findings on clinical examination. Given the diagnostic limitations of previous chest radiographs, spiral computed tomography was performed to investigate the cause of her breathlessness. This showed a right sided pneumothorax on all cuts of the tomogram (fig 1). It is most probable that the pneumothorax re-accumulated because of a further air leak after the removal of the chest drain. A second intercostal drain was re-inserted; a subsequent tomogram showed that both lungs were fully expanded with severe emphysematous change in the right middle and lower lobe and bullous emphysema on the left at the lung base.

Figure 1

Computed tomography showing a right sided pneumothorax.

DISCUSSION

Spontaneous pneumothorax occurs commonly in two groups of patients: otherwise healthy young subjects who can tolerate a large air leak and older patients with emphysema, in whom even a small pneumothorax may cause severe respiratory distress. Clinical and radiological signs may be difficult to interpret, particularly in the presence of severe COPD, large bullae may mimic pneumothoraces. National guidelines have been published to assist clinical management.1

A radiological diagnosis of pneumothorax can be made only by identifying the visceral pleural line. In the erect person, pneumothorax is first evident near the apex of the chest as air rises to the apex of the hemithorax. In the vast majority of cases, the inspiratory chest radiograph is the only imaging modality required for diagnosis. When pneumothorax is strongly suspected but a pleural line is not identified (possibly obscured by an overlying rib), gas in the pleural space can be detected by either radiography in the erect position in full expiration (the lung density is increased and volume of gas in the pleural space is constant, thus making it easier to detect the pneumothorax) or by radiography in the lateral decubitus position2 (air rises to the highest point and is more clearly visible over the lateral chest wall than over the apex). When patients with suspected pneumothorax have to be examined in the supine position, gas within the pleural space rises to the vicinity of the diaphragm. Depending on the size of the pneumothorax, the result can be an exceptionally deep radiolucent costophrenic sulcus (deep sulcus sign),3 a lucency over the right or left upper quadrant, or a much sharper than normal appearance of the hemidiaphragm with or without the presence of a visceral pleural line visible above it.4 Other findings include visualisation of the anterior costophrenic sulcus, increased sharpness of the cardiac border, collection of air within the minor fissure, and depression of the ipsilateral hemi-diaphragm.4

Cross sectional imaging has the advantage over conventional radiography of visualising lung parenchyma and the pulmonary vasculature and is now increasingly accessible at the cost of delivering a higher radiation dose. It has been shown to be superior to frontal chest radiography in making a diagnosis of pneumothorax in a supine patient.5

REFERENCES

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