A 7-year-old boy accompanied by his mother presents to your office, complaining of a rash and bilateral knee and ankle pain. He also notes some mild crampy abdominal pain associated with nausea but denies vomiting, diarrhea, and fever. On exam you note the rash seen above. He has swelling around his patellar joints bilaterally, and the area is very painful. There are no palpable abdominal masses. His lungs are clear and the remainder of the physical examination is unremarkable. What complication is this patient at greatest risk for

The correct answer is Intussusception

Intussusception is the telescoping of a portion of the intestine (intussusceptum) into an adjacent segment (intussuscipiens), causing intestinal obstruction and, sometimes, intestinal ischemia. The diagnosis is made by ultrasound. Treatment is with air enema and, sometimes, surgery.

Intussusception usually occurs between the ages of 6 months and 3 years, with 65% of cases occurring before the 1st year and 80 to 90% before 2 years of age. It is the most common cause of intestinal obstruction in this age group.

The telescoping segment causes intestinal obstruction and, finally, prevents blood flow to the intussusception segment (Intussusception.), Causing ischemia, gangrene and perforation.

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