DOI: 10.1148/radiol.2413041063
(Radiology 2006;241:943-944.)
© RSNA, 2006
The Ring-around-the-Artery Sign1
Prachi P. Agarwal, MD
1 From the Department of Diagnostic Imaging, the Ottawa Hospital, Civic Campus, 1053 Carling Ave, Ottawa, ON, Canada K1Y 4E9. Received June 15, 2004; revision requested August 24; revision received September 26; accepted October 26.
Address correspondence to the author (e-mail: prachipragya{at}yahoo.com).
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APPEARANCE
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The ring-around-the-artery sign is seen on lateral chest radiographs as a well-defined lucency along or surrounding the right pulmonary artery (Figure).
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Lateral chest radiograph (close-up view of hilar area) in a 17-year-old boy with asthma with spontaneous pneumomediastinum shows a well-defined lucency (arrows) along the right pulmonary artery due to mediastinal air. This appearance is known as the ring-around-the-artery sign.
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EXPLANATION
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Pneumomediastinum refers to an abnormal presence of air in the mediastinum. It manifests as air outlining normal anatomic structures. When air collects around the mediastinal (extrapericardial) portion of the right pulmonary artery, air is seen as a lucency along or surrounding the artery on a lateral chest radiograph (1). This is the reported appearance of the ring-around-the-artery sign.
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DISCUSSION
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Air can enter the mediastinum via an alveolar rupture, a laceration of the tracheobronchial tree or esophagus, or an extension of extrathroacic air from the neck or retroperitoneum (2).
Alveolar rupture may be a result of elevated intraalveolar pressure (eg, as the result of airway obstruction by a foreign body or mucous plugging in a patient with asthma, mechanical ventilation, blunt trauma, coughing, emesis, or Valsalva maneuver) or damage to alveolar walls (eg, pneumonitis, emphysema, lung fibrosis, or adult respiratory distress syndrome) (3–5). Tracheobronchial or esophageal laceration can be traumatic or iatrogenic (2). Extrathoracic causes of pneumomediastinum include extension of air from the head and neck (eg, from facial fracture, laryngeal injury, or tracheostomy) or from the retroperitoneum (eg, from perforation of a hollow viscus) (3,4).
The clinical manifestation of pneumomediastinum is variable and depends on the amount of air in the mediastinal space. Patients may remain asymptomatic, or they may complain of pleuritic chest pain. The classic finding at physical examination is the Hamman sign (a crunching or clicking sound heard over the precordium, synchronous with the heartbeat), which is seen in 50% of cases (6,7). This sign, however, is not pathognomonic for pneumomediastinum (3). The clinical impression can be confirmed with chest radiography.
Air in the mediastinum can outline various anatomic structures, which can produce different radiologic appearances. In addition to the mediastinal right pulmonary artery, air can outline and elevate the thymus (which can appear radiographically as the thymic sail sign), the ascending aorta, the aortic arch, the major branches of the aorta (which can appear radiographically as the tubular artery sign) (8), the trachea and proximal bronchi (which can appear radiographically as the double bronchial wall sign) (8), and the sternal insertions of the diaphragm and the brachiocephalic veins. Air anterior to the pericardium may be the only radiographic manifestation, and it requires a lateral view for detection (8). Mediastinal air outlining the superior surface of the diaphragm and separating it from the heart can create the continuous diaphragm sign (9). On a lateral view, the same mediastinal air creates the continuous left hemidiaphragm sign (2) due to loss of obscuration of the anterior left hemidiaphragm by the heart, a result of trapped air. Naclerio's V sign (2) is produced by air outlining the descending thoracic aorta and extending laterally between parietal pleura and medial left hemidiaphragm. This sign was originally described in association with esophageal rupture but is not specific for this condition (2). The extrapleural sign is the result of air trapped between parietal pleura and the hemidiaphragm (9).
The ring-around-the artery sign has been described only in case reports of patients with pneumomediastinum secondary to asthma, trauma, subclavian artery catheterization, and cocaine use, as well as in patients without identifiable risk factors (7). Usually, the sign is accompanied by other ancillary signs of pneumomediastinum, and the true incidence of the sign is not known.
In pneumomediastinum, air dissects along fascial planes and collects around the pulmonary artery. Since only a short proximal segment of the right pulmonary artery is intrapericardial, much of the air seen on a lateral radiograph as the ring-around-the-artery sign is extrapericardial (10).
In some cases, a fine lucent line (a Mach band) may be seen along the border of the heart and the aortic arch and should not be confused with pneumomediastinum (11). Computed tomography can be helpful in establishing or confirming a diagnosis of pneumomediastinum (8).
Pneumomediastinum can extend in the apical or retrosternal direction. Apical extension produces a lucent apical cap bounded by a line consisting of both visceral and parietal pleura and can be easily mistaken for pneumothorax. Unlike pneumothorax, however, this sign shows irregularity of the pleural line, is almost always bilateral, shows clear evidence of extending toward the neck, and does not change with patient position (2). It is sometimes challenging to differentiate pneumomediastinum from medial pneumothorax and pneumopericardium. In the absence of various signs, a decubitus radiograph can be helpful. In pneumomediastinum, air varies little with patient movement whereas in pneumothorax, air may rise (2). Pneumopericardium is much less common than pneumomediastinum in adults, and the air is confined to the pericardial sac (2).
While pneumomediastinum itself usually has a benign clinical course, it may have grave implications in cases of perforated viscus or airway laceration. A conservative management is indicated with close clinical and radiographic follow-up (6). Complications include pneumothorax due to stretching and rupture of mediastinal pleura and hypotension due to impaired venous blood flow to the heart (2).
In summary, pneumomediastinum has diverse causes and can be diagnosed at radiography. One can identify air in the mediastinum on a lateral chest radiograph with the ring-around-the-artery sign. However, other signs of pneumomediastinum do appear on conventional chest radiographs, as well.
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FOOTNOTES
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Author stated no financial relationship to disclose.
| A trainee (resident or fellow) wishing to submit a manuscript for Signs in Imaging should first write to the Editor for approval of the sign to be prepared, to avoid duplicate preparation of the same sign.
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References
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- Hammond DI. The "ring-around-the-artery" sign in pneumomediastinum. J Can Assoc Radiol 1984;35:88–89.[Medline]
- Bejvan SM, Godwin JD. Pneumomediastinum: old signs and new signs. AJR Am J Roentgenol 1996;166:1041–1048.[Abstract/Free Full Text]
- Fraser RS, Muller NL, Colman N, Pare PD. Mediastinitis, pneumomediastinum and mediastinal hemorrhage. In: Fraser RS, Muller NL, Colman N, Pare PD, eds. Fraser and Pare's diagnosis of diseases of the chest. 4th ed. Philadelphia, Pa: Saunders, 1999; 2863–2870.
- Cyrlak D, Milne E, Imray TJ. Pneumomediastinum: a diagnostic problem. Crit Rev Diagn Imaging 1984;23:75–117.[Medline]
- Rogers LF, Puig AW, Dooley BN, Cuello L. Diagnostic considerations in mediastinal emphysema: a pathophysiologic-roentgenologic approach to Boerhaave's syndrome and spontaneous pneumomediastinum. Am J Roentgenol Radium Ther Nucl Med 1972;115:495–511.[Medline]
- Piscitelli J, Orshan SG, Heisler L, Rossoff LJ. A case of ring around the artery: spontaneous pneumomediastinum. Chest 1988;93:405–406.
- Berro E, Mehta J, Dralle WM, Williams J. "Ring around the artery" as a presenting feature in undiagnosed asthma with pneumomediastinum. South Med J 1990;83:215–217.[Medline]
- Zylak CM, Standen JR, Barnes GR, Zylak CJ. Pneumomediastinum revisited. RadioGraphics 2000;20:1043–1057.[Abstract/Free Full Text]
- Levin B. The continuous diaphragm sign: a newly recognized sign of pneumomediastinum. Clin Radiol 1973;24:337–338.[CrossRef][Medline]
- Landay MJ, Cohen DJ, Deaton CW Jr. Another look at the "ring-around-the-artery" in pneumomediastinum. J Can Assoc Radiol 1985;36:343–344.[Medline]
- Chasen MH. Practical applications of Mach band theory in thoracic analysis. Radiology 2001;219:596–610.[Abstract/Free Full Text]
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