The small mass underwent ultrasound-guided biopsy which confirmed a diagnosis of demoed-type fibromatosis.
It might surprise you that this can be safely biopsied with ultrasound given the relatively deep position in the mesentery. However, the small bowel loops can often be displaced away from the mass/body wall with gentle compression, essentially bringing the mass up to the body wall. Careful inspection for any peristalsing loops of bowel can be made before advancing the biopsy device. In you are highly concerned by this, a biopsy device can safely pass through small bowel if needed (20 gauge or smaller is recommenced; note that traversing large bowel is higher risk and prep and antibiotics may be considered 1). Thus, ultrasound is actually much safer for this type of biopsy than CT, which would not be safe in this case.