Pneumomediastinum

Air is present in the soft tissues of the neck of an elderly female patient s/p endoscopy performed during an unsuccessful attempt to remove food obstructing the esophagus.
- Subcutaneous emphysema and mediastinal air s/p esophageal perforation can be well seen in the detailed view.
- No pneumothoraces are present.
- No focal infiltrates are identified.
- It is similar to a radiograph of a patient who experienced a traumatic intubation.
The patient was taken to the O.R. and a muscle flap placed to close the perforation and prevent mediastinitis.

Discussion:

As discussed in Armstrong, pneumomediastinum --
- Indicates perforation of respiratory or GI tract.
- Can be secondary to:
  - Alveolar rupture.
    - Spontaneous.
    - S/p compressive trauma to thorax.
    - S/p lung rupture with air tracking into mediastinum via chest wall and neck.
  - Traumatic laceration of tracheal/bronchial tree.
  - Perforation of esophagus.
    - Spontaneous.
    - S/p instrumentation.
  - Perforation of pharynx, duodenum, colon, rectum with tracking of air into mediastinum.
Spontaneous rupture associated with:
- Sudden increased intrathoracic pressure (e.g., coughing, vomiting, asthmatic attack).
- Mechanical ventilation, esp. with non-compliant lungs.
- Strenuous exercise.
- Marijuana smoking.
- Nitrous oxide inhalation.
- Pneumonia.
- Diabetic ketoacidosis.
- Diffuse interstitial pulmonary fibrosis.
- Childbirth.
On radiographs,
- Air dissecting under the thymus in children, gives rise to the so-called "sail" sign.
- Air dissecting beneath the heart and diaphragm produces the "continuous diaphragm" sign.
- Can occasionally be difficult to differentiate from pneumothorax (air often seen over lung apex) and pneumopericardium (air does not ascend above aortic knob or into the superior mediastinum.

Final Note:

While most cases of spontaneous pneumomediastinum rarely require treatment or affect the outcome of a disease, diffuse mediastinitis is considered to be a serious condition with high mortality.
Acute mediastinitis can result from esophageal perforation seen s/p
- penetrating trauma incl. surgery, endoscopy, ingesting sharp objects.
- forceful vomiting (Boerhaave's syndrome).
- Leakage through necrotic neoplasm.
Other causes of acute mediastinitis include
- extension of infection, empyema, etc.

Ref: Armstrong, P., et. al., Imaging of Diseases of the Chest, 2nd ed, Mosby, St. Louis, MO, 1995, pp. 770-776.