A 3-month-old boy presents to the emergency department (ED) with a history of fussiness and inconsolable crying throughout most of the day. His mother states that there is no identifiable cause for his discomfort. He is tolerating feeding and does not have any signs of illness, including cough, nasal congestion, fever, or change in stool pattern. As the day has progressed, the infant's fussiness has subsided, but he has developed purplish discoloration and swelling of the fourth right toe. The mother is concerned that something is constricting the toe and has attempted to find the cause but cannot, which has prompted the visit to the ED.

The infant was born at term after an uneventful pregnancy. He has remained in good health, receiving appropriate immunizations at birth and at 2 months of age. He was circumcised at birth, has never been hospitalized, and has not undergone any other surgical procedure....

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