Spinal fusion on s1,l5,l4. On my 15 yr old son. 3 days ago. We were being discharged when the nurse noticed a "pocket" of swelling about 6inches wide, 4 inches tall and 1/2 inch deep. Thisis located about 1 1/2 inches above incision. The dr is coming to see us in the morning, the nurses are to keep an eye on it tonight. What could we be looking at?