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The point of the needle. Occult pneumothorax: a review
  1. P Gilligan1,
  2. D Hegarty2,
  3. T B Hassan1
  1. 1Department of Accident and Emergency Medicine, The Leeds General Infirmary, Leeds, UK
  2. 2Family practitioner, Leeds
  1. Correspondence to:
 Dr P Gilligan, The Leeds General Infirmary, Great George Street, Leeds LS1 3EX, UK; 


The case of a patient with an unusual medical condition and an occult pneumothorax is presented. The evidence for management of occult pneumothorax particularly in patients with underlying lung disease is reviewed and solutions to the acute clinical problems that may arise are suggested.

  • occult pneumothorax

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A 27 year old man with histiocytosis X presented to the emergency department with left posterior chest wall pain and marked dyspnoea. The patient previously had recurrent pneumothoraces, eight on the right and two on the left. He had undergone pleurodesis of the right lung. His medical history also included invasive bronchopulmonary aspergillosis and an embolisation of the right pulmonary vessels for life threatening massive hemoptysis. He was on two litres per minute of home oxygen, which usually maintained his oxygen saturations around 94%.

On examination he was pale and sweaty with a heart rate of 160 per minute and a respiratory rate of 42 per minute. He had an oxygen saturation of 88% on 15 litres per minute of oxygen and a blood pressure of 76/45 mm Hg. Respiratory examination revealed diminished air entry bilaterally more marked on the left with increased resonance over the anterolateral left hemithorax. His trachea was noted to be central.

Emergency chest radiography was performed but while awaiting the return of the film the patient decompensated further, his saturations decreased to 81%, and his trachea was now deviated to the right. An emergency needle decompression of his left hemithorax was performed. In the context of his complicated medical history and the clinical findings the needle was inserted at the point of poorest air entry and maximal resonance, which was the left sixth intercostal space in the anterior axillary line. Some 300 ml of air was aspirated from the left hemithorax and the patient clinically improved. The chest radiograph revealed bilateral infiltrates and underlying cystic and bullous disease but failed to reveal evidence of a pneumothorax (fig 1). A chest radiograph performed after the needle decompression also failed to show a pneumothorax. Computed tomography (CT) of the thorax revealed an anterior pneumothorax (fig 2). This was drained under CT guidance by the placement of a chest drain catheter.

Figure 1

Chest radiograph consistent with underlying histiocytosis X but no obvious pneumothorax.

Figure 2

CT scan showing an anterior pneumothorax.

During the patient’s in hospital stay his chest drain was removed as his chest radiograph showed no evidence of residual pneumothorax. The patient became markedly dyspnoeic within 24 hours. Because of the clinical impression of the recurrence of the tension pneumothorax the patient had a needle decompression performed in the classic manner. The needle placed initially at the second intercostal space in the left midclavicular line failed to permit aspiration of air. An attempted needle decompression at the fourth intercostal space in the mid-axillary line was also unsuccessful. Urgent CT again confirmed a left sided anterior pneumothorax. A chest drain catheter was placed under CT guidance. The patient was discharged from hospital 23 days later. Resolution of the pneumothorax was confirmed by CT before discharge.


Diagnosing a pneumothorax in patients with chronic lung disease may be difficult. Chest radiography may fail to show a pneumothorax—that is, an occult pneumothorax. How is occult pneumothorax best diagnosed and treated?


A search of the literature was undertaken using occult pneumothorax and its associations—that is, “OCCULT”.mp.OR “VENTRAL”.mp. OR “SUPINE”.mp. OR “LOCALISED”.mp. OR “LOCALIZED”.mp. OR “DIFFICULT” OR “HIDDEN”.mp. AND PNEUMOTHORAX/ or “PNEUMOTHORAX”.mp.and “TENSION”.mp. The limits to human and english language were applied. The search was performed using: Medline from 1966 to December 2000; Best evidence 1991 to the present; The Cochrane Database of systematic reviews, issue 3, 2000; Cinahl 1982 to October 2000; Database of abstracts of Reviews of effectiveness 3rd quarter 2000; the emedicine database; a search of the relevant bibliographies.

Key points

  • Chest radiography remains the first approach to the diagnosis of pneumothorax, but it may fail to show the presence of all pneumothoraces, particularly where there is underlying lung disease.

  • Tension pneumothorax is a clinical diagnosis requiring emergency needle decompression but this may be unsuccessful in loculated pneumothoraces.

  • CT is the gold standard for the diagnosis of occult pneumothorax. It is extremely useful with regard to management decisions and can help in the performance and the assessment of the efficacy of interventions.

The relevant articles are included.

In most patients pneumothorax is readily detected.1 Radiological confirmation of the diagnosis is based on the ability to observe the lucent band of air between the visceral and parietal pleura and recognising the opaque pleural stripe on the chest radiograph.2 The association between Langerhan’s histiocytosis X and pneumothoraces is well publicised, with the occurrence of pneumothorax in these patients being about 25%.3–7 In patients with cystic lung disease, the diagnosis of pneumothorax based on plain chest radiography alone may be difficult. Phillips et al noted that the complex appearance of the lungs themselves or partial adherence of the lung to the chest wall because of surgery or inflammation, or both of these factors, may result in an unusual configuration of the pneumothorax or mask it altogether.6

Occult pneumothorax has been defined as pneumothoraces seen on CT scans but not on routine chest radiographs.8–11 Missed pneumothorax, which is a separate entity, may be defined as a pneumothorax that was seen on retrospective review of the chest radiograph but was small or subtle enough not to be diagnosed prospectively.12 The phenomenon of occult pneumothorax is well described in the trauma literature with an incidence of between 2% and 12%.8 Hehir et al postulated that part of the problem with regard to trauma patients and the phenomenon of occult pneumothoraces was attributable to the fact that the chest radiographs were often taken supine, suboptimally, and soon after arrival, whereas chest injury may take time to become apparent. They found that pneumothorax was the most commonly missed abnormality on chest radiography in their study of 100 trauma patients.13 Occult pneumothorax has also been described in medical patients. Carr et al in a case series of nine patients with bullous emphysema on whom they performed CT as part of the preoperative assessment of bullous emphysema found it to be useful in assessing the extent of the disease and coincidentally they noted one of the patients had an occult pneumothorax.14

Tagliabue in a review of 74 ARDS patients found an occult pneumothorax rate of one in three. Interestingly ineffective position of the thoracostomy tube was found in 13 of 20 patients.15


What are the investigation options in patients with a possible pneumothorax particularly with chronic lung disease.

Chest radiography

As previously stated, occult pneumothorax is a pneumothorax identified by CT scan but not seen on conventional radiographs.16 Carr et al in a cadaveric study found that the ability of radiologists to diagnose pneumothorax varied with cadaver position and was dependent on the volume of air. The left lateral decubitus view was apparently the most sensitive for diagnosing pneumothorax on plain radiographs.17

Kollef et al in their prospective case series of 464 adult ICU patients found that atypical radiographic location of the pneumothorax contributed to the failure to diagnose it initially.18 In common with other authors Kolleff recomended obtaining additional views, such as cross table lateral, lateral decubitus, or full expiratory views.17,19,20 Jantsch et al in their study on 55 ICU patients with sudden deterioration of gas exchange and negative AP chest radiography found that in 14 (33%) of 42 cases a tangential view revealed a pneumothorax.21

Thoracic ultrasonography

Lichtenstein et al reported a study in which they described and evaluated lung sliding, an ultrasound finding the absence of which was seen in all 43 (100%) cases of pneumothorax. They concluded that ultrasound was a sensitive test to detect pneumothorax.22 Goodman et al in a prospective blinded study comparing CT, ultrasound, and erect chest radiography after 41 CT guided biopsies found ultrasound more sensitive than erect chest in the detection of pneumothorax.23 Lichtenstein et al in a prospective clinical study found that vertical ultrasound artefacts (comet tail artefact) present at time of ultrasound was not found if a pneumothorax was present.24

Ultrasound may therefore have a useful role in early diagnosis of occult pneumothorax particularly in the form of bedside ultrasonography, which may facilitate rapid diagnosis and localisation of the pneumothorax in the resuscitation room.

Computed tomography

Bungay et al in a study of 88 consecutive CT guided lung biopsies found that CT was more sensitive as it detected 35 pneumothoraces as compared with the 22 that were picked up by chest radiograph. CT picked up smaller and shallower pneumothoraces than conventional chest radiography.25 Phillips et al in their article on the role of CT in the management of pneumothorax in patients with complex cystic lung disease advocated the use of CT in such patients when they become acutely breathless and the plain radiograph either fails to reveal the presence of a pneumothorax, although one is suspected, or fails to provide sufficient information to allow management decisions to be made.6


The treatment of primary pneumothorax has been controversial since the 1960s. Patients with severe breathlessness or those with signs consistent with a tension pneumothorax obviously require immediate drainage.26

The major complication of any pneumothorax is the potential for a tension pneumothorax to develop that may be rapidly fatal and must be excluded immediately in all patients regardless of aetiology.27 The British Thoracic Society have defined a tension pneumothorax as any pneumothorax with cardiorespiratory collapse and they advise immediate decompression.30 In patients with minimal pulmonary reserve, even a small pneumothorax can have adverse haemodynamic effects or cause tension that rapidly induces cardiovascular collapse and death.18,29–31 Baumann et al note that the physiological hallmark of tension pneumothorax is that intrapleural pressure exceeds the atmospheric pressure throughout the respiratory cycle. They also warn that previous studies have shown a fourfold increase in deaths when the treatment of the tension pneumothorax was delayed awaiting radiographic confirmation.32

In a patient with an occult pneumothorax without significant cardiorespiratory compromise the aims of treatment are the same as for spontaneous pneumothorax. Baumann et al defined the goals of treatment of a pneumothorax as eliminating intrapleural air, facilitating pleural healing, and attempting recurrence prevention.33

Sahn and Heffner in their review of spontaneous pneumothorax listed the therapeutic modalities available as follows:

  • Simple observation

  • Supplemental oxygen (this accelerates the reabsorption of air by the pleura by a factor of four, which occurs at a rate of 2% per day in patients breathing room air.)

  • Simple aspiration with a catheter, with immediate removal of the catheter after the pneumothorax has been evacuated.

  • Chest tube insertion

  • Pleurodesis

  • Thoracoscopy

  • Video assisted thoracoscopic surgery

  • Thoracotomy and pleural surgery34

Occult pneumothorax may create its own therapeutic problems. Reinhold et al in a retrospective study of 42 consecutive patients who underwent percutaneous catheter drainage of pleural collections concluded that ease of placement, comparable success rate, and safety of radiologically placed catheters make them an attractive alternative to surgically placed chest tubes.35 With regard to the removal of drainage devices in occult pneumothorax, failure to detect a pneumothorax on conventional radiographs should not be among the criteria for removal. As seen by our patient’s in hospital course if possible CT resolution should be confirmed.


If tension pneumothorax is suspected it should be treated with immediate decompression. If needle decompression fails then consider an alternative site of insertion of the needle or image guided definitive drainage. When the occult pneumothorax is not under tension CT scan will help to guide treatment. Phillips et al in their article on the role of CT in the management of pneumothorax in patients with complex cystic lung disease advocated the use of CT in such patients when they become acutely breathless and the plain radiograph either fails to reveal the presence of a pneumothorax, although one is suspected, or fails to provide sufficient information to allow management decisions to be made.6

Figure 3 shows a suggested algorithm for the treatment of occult pneumothorax.

Figure 3

Suggested algorithm for management of occult pneumothorax.



Peadar Gilligan treated the patient, initiated, the review, and wrote the paper. He also acts as guarantor for the paper. Deirdre Hegarty advised on the structure and content and edited the paper. Dr Taj Hassan contributed to the writing and formulation of the review and advised on its structure and edited the paper.