A 15-day-old boy after intracardiac repair was discharged from the intensive care unit with a low-flow nasal cannula for oxygen administration. The cannula was a 4-Fr multi-purpose tube with a side hole that was inserted into his left nostril. Next day, he suddenly developed pneumocephalus emerging from the right periorbital swelling and extending to his face and subcutaneous scalp over the next 6 h. A computed tomography (CT) scan revealed massive air pockets in the orbit, subdural space, subcutaneous scalp, and face. The nasal cannula was found to have been inserted deeper than we thought and was thus presumed to be the source of the air pockets. We immediately removed the cannula. Follow-up CTs revealed rapid resolution of the intracranial and subcutaneous air. The subcutaneous emphysema completely disappeared over the next 4 days, and he was discharged without any incident.