Annals of the Royal College of Surgeons of England (1987) vol. 69 The supine pneumothorax DAVID A P COOKE FRCS Surgical Registrar, Department ofSurgery, St Thomas' Hospital JULIE C COOKE FRCR* Radiological Senior Registrar, Department ofDiagnostic Radiology, Brompton Hospital, London Key words: PNEUMOTHORAX; COMPUTI ED TOMOGRAPHY; TRAUMA Summary TABLE I Causes of a pneumothorax The consequences of an undiagnosed pneumothorax can be life- threatening, particularly in patients with trauma to the head or Broncho-pulmonay pathology Traumatic injuy and in those mechanical ventilation. Yet multiple requiring Asthma it is these patients, whose films will be assessed initially by the Bronchial adenoma surgeon, who are more likely to have a chest X-ray taken in the Bronchial carcinoma Penetrating trauma supine position. The features of supine pneumothoraces are de- Emphysema Blunt trauma scribed and discussed together with radiological techniques used to Fibrosing alveolitis Inhaled foreign body confirm the diagnosis, including computed tomography (CT) Idiopathic which may be ofparticular importance in patients with associated Marfan's syndrome fatrogenic cranial trauma. Pulmonary abscess Pulmonary dysplasia CVP line insertion Introduction Pulmonary infarct Jet ventilation Pulmonary metastases Liver biopsy In a seriously ill patient or the victim of multiple trauma Pulmonoalveolar proteinosis Lung biopsy the clinical symptoms and signs of a pneumothorax may Radiation pneumonitis Oesophageal instrumentation be overshadowed by other problems. Usually in these Sarcoid PEEP ventilation circumstances a chest X-ray will be taken at the bedside Staphylococcal septicaemia Pleural aspiration with the patient supine and the appearances of a Tuberculosis Pleural biopsy pneumothorax will be different from those seen when the Tuberose sclerosis patient is upright. On an erect chest radiograph the familiar apical crescent of air between the pleural sur- and air is seen at the apex of the chest showing the faces is easily recognised; however, when supine, any free familiar appearance of the lung edge parallel to but air will be demonstrated in a different distribution. In separated from the chest wall. the first instance the casualty officer or junior surgeon In the supine position gravity causes the lung to fall will have to assess the films and may not appreciate the dorsally allowing the air to collect anteromedially. The significance of these abnormalities leading to a delay in appearance of a small or moderate quantity of air in this appropriate treatment. The aetiology, pathology and position may not be appreciated although a greater diagnosis of the condition is discussed and illustrated quantity of intrapleural air permits further lung retrac- with examples from our experience. tion revealing the familiar pleural line parallel to the lateral chest wall. Physiology Aetiology The visceral and parietal pleural surfaces are usually A great variety of conditions can precipitate a kept in close contact by virtue of the considerable forces the largest category however of surface tension exerted by the thin film of fluid nor- pneumothorax (Table I) present. Air between the being labelled idiopathic (1) although usually caused by mally pleurae allows elastic rupture of an apical pulmonary parenchymal bleb (2). recoil of the pulmonary parenchyma and realisation of However when the the potential space. As the lung is heavier than air, even considering patients in whom a when hyperinflated, it falls to the bottom of any air- supine chest radiograph might be requested, the aetiol- Tethered the ogy most likely to be encountered is that of trauma containing cavity. medially by bronchus, or otherwise. vessels and pulmonary ligament, movement occurs iatrogenic about this hinge and free air collects in the uppermost Radiographic appearances of a supine pleural recess. Thus when a patient with a pneumothor- pneumothorax ax is x-rayed in the erect position the lung falls inferiorly In the supine position air may collect in one or more of the pleural recesses, anteromedial, posteromedial and *Present appointment: Senior Registrar, Department of Radi- costophrenic, or in the subpulmonary spaces. In examin- ology, Royal Marsden Hospital, London SW3. ing the supine radiograph air should be sought particu- Correspondence to: D A P Cooke, Department of Surgery, larly in these locations, the appearances of which are St Thomas' Hospital, London SEI 7EH. described below. The supine pneumothorax 131 .:~~~~~~~~~~ H-4.,",=:_t FIG. 3 Radiograph showing posteromedial air behind the right Fic. 1 Chest X-ray showing radiolucent band between the cardiac border, apparently extending below the hemi- heart border and the lung. diaphragm. FIG. 2 CT scan of a patient with a right pneumothorax z7 I showing air anteriorly and medially. Note the anterior pleural FIG. 4 Radiograph showing the subpulmonary air lying line undisplaced in this patient. between the right lung and hemidiaphragm. ANTEROMEDIAL notably the thymus which is seen as a triangular or In the supine position the anteromedial pleural recess is sail-shaped density, whereas in the medial pneumothor- the least dependent space within the thoracic cage and ax the air is confined by the mediastinal pleura (4). air most commonly collects here producing a dark Mediastinal air is more commonly distributed bilaterally radiolucent band, parallel to the cardiac outline, be- detailing both sides of the thymus and heart, but the air tween the medial aspect of the lung and the mediasti- can move less readily than that within the pleura. Gentle num. (Fig. 1) Air in this position will make the cardiac rotation of the patient before repeating the X-ray will contour more sharply defined than usual (3). It is easy to relocate the pleural air but mediastinal air will be un- overlook this paramediastinal lucency and, even if recog- changed. nised, the volume of air present may be underestimated. The position at which the pleural surfaces of the two It is important to distinguish between a pneumo- lungs come into contact can be seen as a thin vertical line mediastinum and a medial pneumothorax. In the former in the anterior mediastinum, projected over the trachea air spreads to outline structures within the mediastinum, which is very easily demonstrated on CT (Fig. 2). As air 132 D A P Cooke andJulie C Cooke _ Z Z _s. ]. li FIG. 7 Generalised hiyperlucency of the left hemithorax is indicative of a pneumothorax. FIG. 5 The anterior costophrenic sulcus (arrowed) can be distinguished from the dome of the diaphragm (double arrows). These, together with a lucent upper abdominal quadrant, indicate free pleural air. FIG. 8 Free air delineates the adjacent diaphragm and inferior heart border. neonate than in the aduit. For reasons unexplained, this happens more frequently from right to left than vice versa. Lastly mediastinal shift cannot occur as a result of a pneumomediastinum but is not uncommon with a FIG. 6 Radiograph showing deep left lateral costophrenic pneumothorax. sulcus. POSTERMEDIAL accumulates in the anteromedial recess pleura from the Although it is difficult to conceive why air should lie affected side bulges across the midline herniating into the posteriorly with the patient lying supine it has been contralateral hemithorax and the line is displaced. The suggested that the rare finding ofair in the posteromedial anterior mediastinal line is not visible in infants as the recess is due to the collapse of the overlying lobe of lung thymus separates the medial pleural surfaces but pleural in the presence of pneumothorax. The air is seen over- herniation does occur, indeed more commonly in the lying the cardiac shadow but the inferior limit can be The supine pneumolhorax 133 traced to below the anterior costophrenic line (5) (Fig. sufficient to produce the contrast needed to distinguish 3). these two structures (Fig. 8). SUBPULMONARY API(:AIL PERICARI)IAIL FAT TAGS The second most frequent collection of air on the supine Discrete lobulated densities 1-1.5 cm in diameter, which film is in the subpulmonary space (6) which appears as a represent apical pericardial fat tags are also made visible basal radiolucent stripe bounded above by a thin hairline by the thin layer ofair outlining the cardiac apex (9) and of visceral pleura parallel to the dome of the hemi- they may change shape when not compressed by adja- diaphragm (Fig. 4). In fact the concavity of the lung base cent lung tissue. Any alteration in the contour or con- may allow air to collect here even if the patient is moved figuration of the cardiac fat pads in successive chest to an erect position. The air must be distinguished from X-rays should alert the observer to the presence of a traumatic herniation ofintestine and the observer should developing pneumothorax. look carefully for bowel markings. Performing a decubi- tus film will demonstrate the redistributed pleural air at Hydropneumothorax and haemopneumothorax the lateral margin of the lung whereas any intestinal air If the pleural line is identified lying away from the chest will remain beneath the lung base and may show air- wall and yet the space lateral to it is of greater density fluid levels. than the lung parenchyma, then there is fluid within the pleural cavity which may influence the positioning of the COSTOPHRENIC SULCUS chest drains (10). Free air collecting in the lateral costophrenic recess causes the sulcus to appear deeper than usual (7) (Fig. Discussion 5). Comparison should be made with the other side Seriously ill patients are more often x-rayed supine and although this may not help if there is a bilateral air leak. into this group fall those most likely to have a Air in the anterior costophrcnic sulcus appears as an pneumothorax. A leak of air into the pleural space can oblique line projected over the upper abdominal quad- develop into a life threatening tension pneumothorax but rant (Fig. 6). Frec pleural air will enable this anterior even if this problem does not develop, respiratory im- attachment of thc diaphragm to be distinguished from the pairment may accompany a moderate sized dome.