A 26-year-old male presen...

A 26-year-old male presents to the emergency department complaining of sudden-onset severe chest pain radiating to the upper back for the past 3 hours. He denies any fevers or chills but reports an episode of syncope prior to arriving to the hospital. He is unable to remain still secondary to pain. His past medical history is negative. On initial exam, his blood pressure is 140/50 mmHg, and heart rate is 102/min. He appears to be tall and thin, with long arms, long thin fingers, and hypermobile joints. His sternum has a concave deformity. Cardiac examination reveals a regular rhythm. Breath sounds are equal bilaterally without crackles. ECG demonstrates nonspecific ST-segment changes. Troponin and CK-MB are within normal ranges. A chest x-ray demonstrates a widened mediastinum. Kindly suggest the appropriate diagnosis?