An adolescent with acute abdominal pain and bowel wall thickening

A 15-year-old girl was admitted with acute crampy abdominal pain and repeated vomiting over the preceding 2 hours; no fever, diarrhoea or abdominal trauma was reported. She had started oestrogen-progestin contraception 3 months ago. She had sought medical advice twice in the previous weeks for self-limiting episodes of right hand swelling, without urticaria. On examination, she was unwell and in pain, with severe tenderness in the right lower quadrant, without guarding or rebound tenderness. Bowel sounds were diminished. Blood tests were unremarkable. Two hours after admission, an abdominal ultrasound scanning showed an impressive wall thickening (>1 cm) of the terminal ileum, caecum and ascending colon (figure 1). Abundant free intraperitoneal fluids in the pelvis and in the hepatorenal recess were present. Figure 1Marked caecal wall thickening evidenced at the ultrasound scanning. QUESTIONS: Which of the following is the most likely diagnosis in this patient? Ileocolic intussusceptionGastrointestinal manifestation of Henoch-Schönlein purpuraAbdominal attack of hereditary angioedema (HAE)Acute pancreatitisWhich of the following blood tests may help to confirm the diagnosis? Erythrocyte sedimentation rateC4Serum amylase: 36 IU/LC1-inhibitorHow should this patient be evaluated and treated?