'Pneumoma' under a healed sternotomy wound

A 45-year-old woman had undergone coronary artery bypass surgery. About a month after discharge, she complained of persistent painless swelling at the upper end of a well-healed sternotomy scar (Fig. 1). On examination, the 2.5 x 2 cm swelling was compressible but non-fluctuant. Needle aspiration yielded only air. An x-ray of the swelling obtained on a dental plate showed a subcutaneous collection of air (Fig. 2).