What causes the spinnaker sail sign on the neonatal chest radiograph?
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Answer:
The spinnaker sail sign is elevation and lateral displacement of both thymic lobes by air in the mediastinum, so that each lobe is outlined as a triangular opacity billowing away from the cardiac silhouette. It is a specific radiographic sign of pneumomediastinum in the neonate. The angel wing sign is the same sign under a different name, the two lobes lifted symmetrically resembling a pair of spread wings; it is not a sign of absent pectoralis muscle. It must be distinguished from the normal thymic sail sign, in which a normally positioned thymic lobe simply projects as a triangular sail beside the heart in a healthy infant. In the spinnaker sail sign the thymus is displaced upward and outward and is separated from the cardiac border by a lucent band of gas, which the normal variant never shows. It accompanies the other features of mediastinal gas: the continuous diaphragm sign, the ring-around-the-artery sign, and lucent streaks along the mediastinal contour.
Why is it called so?
The thymic lobe lifted away from the mediastinum by gas resembles a spinnaker, the large triangular foresail of a yacht, filling with wind.
Pathophysiology
Alveolar overdistension, from resuscitation, mechanical ventilation, meconium aspiration or spontaneous rupture, allows gas to escape into the perivascular interstitium and dissect centrally along the bronchovascular sheaths, the Macklin effect. On reaching the mediastinum the gas collects in the loose areolar tissue around the thymus. Because the neonatal thymus is a soft, mobile structure attached at its base but free superolaterally, the accumulating gas lifts it off the pericardium and displaces it upward and laterally, silhouetting its inferior surface and rendering the lobe as a discrete triangular opacity.
Alternative names: Angel wing sign, thymic spinnaker sail sign
Other associated named signs: Continuous diaphragm sign, ring-around-the-artery sign, double bronchial wall sign, V sign of Naclerio, and the normal thymic sail sign
References
Access all radiology signs posted so far: https://radiogyan.com/radiology-signs/
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