Teaching Case

A 77 year old female patient with unremarkable history, who developed pulmonary fibrosis, evaluated for dyspnoea and cough.

A 77 year old woman was referred to the emergency department with worsening of cough episodes and dyspnoea. The patient has no history of connective tissue disease.
A PA and lateral chest radiograph taken at the time of admission showed the occurrence of pneumomediastinum and diffuse reticular opacities in both lungs (Fig 1).
The chest CT (Fig 2) demonstrated extensive pneumomediastinum with diffuse interstitial thickening in both lungs with multiple traction bronchiectases.

Pneumomediastinum (PNMD) is characterized by the presence of gas in mediastinal tissues outside the oesophagus and the tracheobronchial tree, which almost invariably originates from the alveolar space or the conducting airways. Many authors distinguish spontaneous PNMD as a form of pneumomediastinum that is not associated with blunt force or penetrating chest trauma, endobronchial or oesophageal procedures, neonatal lung disease, mechanical ventilation, chest surgery or other invasive procedures.
The association between lung fibrosis and pneumomediastinum is well known. The pathogenesis responsible for pneumomediastinum in this case is due to alveolar or honeycomb cyst rupture due to increased intrapulmonary pressure on strain with consequent dissemination of air through the blood vessel sheath to the mediastinum.
Manoeuvres that usually precede spontaneous pneumomediastinum are those that involve an increase in lung volume followed by a dramatic increase in pleural pressure, such as coughing, sneezing, vomiting, or parturition. Patients with PNMD commonly report transient stabbing chest pain, which may radiate to the shoulders, arms or back. The pain is usually located substernally and worsens with movement, breathing or position change. They tend to have dyspnoea and coughing. Dysphagia and dysphonia may also be present if retropharyngeal or perilaryngeal air dissection is present. Pneumomediastinum is difficult to diagnose at physical examination alone. The diagnosis is usually made following imaging studies. The radiographic signs depend on the depiction of the normal anatomic structures that are outlined by the air as it accumulates in the mediastinum.
Infants and young adults with pneumomediastinum may have the "thymic sail sign" in which the thymic lobes are shifted upward resembling a sail. Air anterior to the pericardium is a frequent manifestation and requires a lateral view for diagnosis.
Streaks or pockets of air outlining visceral planes or tissue compartments can also be seen and constitute air surrounding the pulmonary artery or its branches and mainly involve the intramediastianal segment of the right pulmonary artery. When there is air adjacent to the major branches of the aorta both sides of the vessel depicted.
When air resides along a major bronchus, the bronchial wall visualized giving the double bronchial wall sign. A thin, radiolucent line at the left heart border or a "continuous diaphragm" (unbroken radiolucent line from one hemi-diaphragm to the other beneath the heart) is usually present when air is trapped posteriorly to the pericardium. Air between the parietal pleura and the diaphragm can produce the extrapleural sign.
CT scan is used to better visualize pneumomediastinum not seen on plain x-ray or to provide further information on coexisting disease or causes for the patient's presentation.
Therapeutic procedures are generally not necessary. Spontaneous pneumomediastinum typically resorbs within a period of 1 to 2 weeks without treatment, and rarely recurs.