59 years old male in intensive care unit with sudden subcutaneous crepitation

Case provided by Viktoria

History
A 59 years old male with severe pneumonia, ARDS, and prolonged mechanical ventilation.

Imaging findings
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).

Diagnosis
Extensive soft tissue emphysema associated with mechanical ventilation.

Discussion
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.

Teaching points

  • 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.

Recommended reading

Ioannidis et al.
Barotrauma and pneumothorax.
J Thorac Dis. 2015; 7(Suppl 1), S38–43.
http://jtd.amegroups.com/article/view/3909/html

Maunder et al.
Subcutaneous and mediastinal emphysema. Pathophysiology, diagnosis, and management.
Archives of Internal Medicine. 1984; 144 (7), 1447–1453
http://jamanetwork.com/journals/jamainternalmedicine/article-abstract/604688

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s