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Neuroradiology Case of the Week
Case 401
April 2009
Bruce Chien, MSIII, Virendra Kumar, MD and PL Westesson, MD, PhD, DDS
Clinical
Presentation: Patient is a 9-year-old female with a tracheal laceration who fell while playing on the monkey bars striking her anterior neck against the ladder of the monkey bars.
Imaging Findings: Diffuse subcutaneous emphysema is seen involving the bilateral carotid, retropharyngeal, bilateral parapharyngeal spaces. Air is seen extending into the mediastinum which shows large amount of pneumomediastinum. An opening on the anterior tracheal wall is noted without any compromise of airway. A minimal pneumothorax located in the right lung field and a moderately sized pneumothorax in the left lung field is present.
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| Figure 1: Neck CT with contrast reveals air occupying the retropharyngeal and carotid spaces. |
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Figure 2: Neck CT demonstrates tracheal rupture and possible source of pneumomediastinum.
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| Figure 3: Chest CT demonstrates diffuse infiltration of air into the mediastinum. |
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| Figure 4: Chest CT demonstrates a moderately sized pneumothorax in the left lung field. |
Diagnosis: Pneumomediastinum
Discussion: Pneumomediastinum or mediastinal emphysema is the presence of air or gas in the mediastinum. The source of gas may originate from many sources including the upper respiratory tract (facial fractures, dental procedures, head and neck infections), intrathoracic airways (blunt or penetrating trauma, foreign body), disruption or rupture of alveoli (acute or chronic lung diseases), GI tract (esophageal, gastric or intestinal perforations, gas-producing infections) iatrogenically (bronchoscopy, needle aspirations, biopsies), elevation of alveolar pressures (crying, Valsalva, child birth). Spontaneous pneumomediastinum usually results from rupture of alveoli leading to air dissecting along peribronchovascular sheaths and spreading into the mediastinum. The air then moves through mediastinal fascia planes and spreads to subcutaneous tissues of the thorax, upper limbs and cervical region.
Patients with pneumomediastinum 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 dyspnea and coughing. Dysphagia and dysphonia may also be present if retropharyngeal or perilaryngeal air dissection is present. Pneumomediastinum is difficult to diagnose with the physical exam alone. There may be decreased dullness to percussion over the chest. Hamman's sign (crunching or clicking sound heard over the precordium and increased in intensity with inspiration at the left lateral decubitus position) may be present. Subcutaneous crepitations suggest the presence of free air in the thoracic cavity.
The diagnosis is usually made following imaging studies. Plain chest radiography will reveal air within the mediastinum. A thin, radiolucent line at the left heart boarder or a "continuous diaphragm" (unbroken radiolucent line from one hemi-diaphragm to the other beneath the heart) is usually present. Streaks or pockets of air outlining visceral planes or tissue compartments can also be seen. Infants with pneumomediastinum may have the "thymic sail sign" in which the thymic lobes are shifted upward resembling a sail. CT scan is used to better visualize pneumomediastinum not seen on plain x-ray or to provide further information on coexisting illness or causes for the patient's presentation.
The prognosis with patients who develop pneumomediastinum tends to be reassuring with morbidity and mortality attributed to underlying disease or precipitating events. The air usually spreads throughout the mediastinum and subcutaneous tissue planes and resolves spontaneously as long as the source of the air infiltration has been sealed or precipitating event resolved. Conservative management (pain control, supplement oxygenation) and careful observation is usually all that is needed. Bronchoscopy is performed if tracheobronchial perforation is suspected. Cardiovascular collapse from decreased cardiac output or venous return secondary to cardiac compression is a life-threatening event that may occur in patients with pneumomediastinum. Invasive procedures such as needle aspirations, infraclavicular incisions, cervical mediastinotomy, subcutaneous drains and tracheotomy may be needed.
References:
- Winnie GB. Chapter 411 – Pneumomediastinum. IN: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics, 18th ed. Philadelphia: Elsevier Saunders, 2007. [MDConsult]
- Part DR, Vallieres E. Chapter 72 - Pneumomediastinum and Mediastinitis. IN: Mason RJ, Murray JF, Broaddus VC, Nadel JA, eds. Murray and Nadel's Textbook of Respiratory Medicine, 4th ed. Philadelphia: Elsevier Saunders, 2005. [MDConsult]
- Carolan PL, Vaughn DJ. Pneumomediastinum. eMedicine. December 12, 2008. http://emedicine.medscape.com/article/1003409-overview.
- Chalumeau M, Le Clainche L, Sayeg N, et al. Spontaneous pneumomediastinum in children. Pediatr Pulmonol. 2001 Jan;31(1):67-75. [PubMed]
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