AN 11-YEAR-OLD white girl was brought to the emergency department by her parents with the complaint of swelling in her neck, which she had noticed while dressing that morning. She otherwise felt perfectly well and denied chills or fever and had no weight loss, symptoms of upper respiratory infection, breathing complaints, or neck pain. Her pediatrician had seen her about 3 weeks earlier for symptoms of upper respiratory infection, which had been treated with antibiotics and had resolved. Her medical history was otherwise unremarkable. She had no history of travel or tobacco use. She did have 2 grown cats but denied scratches. Her family history was remarkable for a maternal aunt with Hodgkin lymphoma.