Case provided by Viktoria
A 59 years old male with severe pneumonia, ARDS, and prolonged mechanical ventilation.
The thoracic plain film radiograph (image A) shows striated subcutaneous hyperlucencies along the lateral chest wall and the cardiac outline compatible with subcutaneous emphysema and pneumomediastinum. The abdominal and thoracic CT scan (images B, C and D ) confirms extensive gas collections in cervical, thoracic and abdominal soft tissues involving subcutaneous fat and deeper compartments including mediastinum and retroperitoneum. In the lung there is also cystic destruction of pulmonary parenchyma (image D).
Extensive soft tissue emphysema associated with mechanical ventilation.
Mechanical ventilation may induce ventilator associated lung injury (VALI) due to large distending volumes (volutrauma) and/or high airway pressures (barotrauma). Volutrauma and barotrauma are defined as the presence of extraalveolar air in locations, where it is not normally found in mechanically ventilated patients. They result from rupture of hyperinflated alveoli and air leak into surrounding tissues. Air can be introduced along the perivascular sheaths into the mediastinum. When air accumulates in the mediastinum it is decompressed along cervical and abdominal fascial planes. In case of rupture of parietal or visceral pleura pneumothorax will appear. Intrapulmonary sequelae are interstitial pulmonary emphysema (more frequent in children), tension lung cysts, and hyperinflation of the lower lobes. Major risk factor for developing VALI is a severe underlying lung disease (e.g., ARDS, chronic obstructive pulmonary disease).
Clinical findings of soft tissue emphysema in general may be subtle. In palpation, a subcutaneous crepitation can be found. This will be more prominent in auscultation. Extensive soft tissue emphysema can result in diffusely swollen skin especially in thorax, neck, head and eyelids. Frequently, dyspnea and difficulty in swallowing occur.
Causes of soft tissue emphysema other than VALI are:
- Iatrogenic (chest surgery; tracheostomy; intubation; chest tube)
- Trauma (stabbing; rib fracture; barotrauma from diving injuries; rupture of trachea, esophagus, bullae)
- Necrotizing skin infections
CT is indicated not only to define the extension of the emphysema, but primarily to confirm the presumed cause. Tracheal or esophageal discontinuity, hematoma and predominance of paratracheal or paraesophageal gas collections may suggest rupture or fistula. Catheters and tubes must be evaluated for dislocation, penetration and fracture.
- Soft tissue emphysema may be a result of ventilator associated lung injury in mechanically ventilated patients.
- CT is indicated especially to rule out other causes of soft tissue edema including perforation of hollow organs and complications of catheter placement.
Ioannidis et al.
Barotrauma and pneumothorax.
J Thorac Dis. 2015; 7(Suppl 1), S38–43.
Maunder et al.
Subcutaneous and mediastinal emphysema. Pathophysiology, diagnosis, and management.
Archives of Internal Medicine. 1984; 144 (7), 1447–1453