Sometimes, Big-Gun Imaging Is Necessary
Case 3: Our third case was a 13-month-old boy with 2 days of abdominal pain and fever, plus elevated WBC count, sedimentation rate, and C-reactive protein. The child lay rigidly in bed, not allowing anyone to roll him over, move his right leg, or touch his lower right abdomen. His examination initially suggested appendicitis. However, both abdominal x-ray and CT scans were normal.
Our differential diagnosis expanded to include pelvic osteomyelitis, diskitis, or an iliopsoas abscess with referred pain to the hip and abdomen.
A bone scan revealed no abnormality of the iliopsoas area, the sacroiliac joint, or the disks. But we were surprised to see an enhanced signal in the soft tissues near the right side of the pelvis.
An MRI (pelvis to thighs) clearly showed a large abscess in his adductor muscle group. The CT, it turned out, had cut off just above the abscess. He dramatically improved within 48 hours after incision and drainage followed by intravenous antibiotics.
Infections of the lower pelvis (pubis or ischium) or nearby soft tissues are difficult to diagnose in children, who have a hard time localizing the pain. In this child's case, the bone scan, which can image the whole body, helped us locate an area of increased vascularity, so we could confidently order the MRI of the correct part of the abscess.
Probably less than 5% of osteomyelitis or soft tissue abscesses are located in the lower pelvis area. With our patient, a key finding was his refusal to allow lateral movement of his right leg. We assumed that meant a problem was in his sacroiliac joint or muscle groups in his back. We didn't think about the muscles right there in his thigh. This was a reminder to us to think outside the “box,” including the lower pelvic bones and the muscles that attach to those bones.
Abdominal CT of an 8-year-old girl shows a large, uniform abscess filling most of the upper half of her kidney. Because its density was so uniform and similar to kidney tissue, ultrasound had missed it.
An MRI reveals osteomyelitis in the distal femur of a 13-month-old limping boy with sympathetic effusion in his knee joint, which had confused the clinical picture.
In a 13-month-old boy with abdominal pain, lower-body MRI captured what a bone scan had helped localize: A large abscess in the adductor muscle group, below the point where a prior abdominal CT scan had cut off. Photo Courtesy Dr. Christopher J. Harrison
