Residual soft tissue and bone edema associated with diagnostic or surgical intervention for suspected osteomyelitis or septic arthritis do not diminish the value of subsequent magnetic resonance imaging in children with persistent signs of infection, a study has shown.
The issue under investigation was whether iatrogenic injury to soft tissue or marrow before an MRI study interferes with the clinician's ability to exclude infection or diagnose alternative causes for symptoms that remain despite a negative result after intervention.
Dr. J. Herman Kan of Vanderbilt Children's Hospital, Nashville, Tenn., and his colleagues conducted a retrospective case-control study using data from patients who underwent emergent contrast-enhanced MRI examinations that were performed for suspected osteomyelitis or septic arthritis at the hospital from March 2002 through September 2007.
Of the initial 136 MRI examinations, the analysis included only the 34 performed within 10 days after an initial diagnostic or surgical intervention, such as joint, marrow, or soft-tissue aspiration; arthrotomy; or incision and drainage of bone or soft tissue. The study control group consisted of 96 patients who underwent MRI for suspected osteomyelitis or septic arthritis during the same period but who did not have a prior intervention.
Pediatric radiologists with additional training in pediatric musculoskeletal radiology performed consensus reviews of the images to assess whether objective MRI criteria could still be applied to those patients who had undergone recent intervention. They also evaluated the presence or absence of specific MRI features of osteomyelitis that could neither be attributed to the recent intervention nor were suggestive of a noninfectious alternative diagnosis. Such features included intraosseous abscess, cortical breach, subperiosteal abscess, and soft-tissue or bone edema, the authors wrote in the November 2008 issue of the American Journal of Roentgenology.
The reviewing radiologists had knowledge of the location of the prior intervention and the final discharge diagnosis, they noted (Am. J. Roentgenol. 2008;191: 1595–600).
In 10 of the 34 study group patients (29%), the MRI findings led to a need for additional intervention, which was similar to the control group, in which the MRI findings pointed to further intervention for 26 of the 96 control group patients (27%), the authors reported. The groups did not differ significantly in the number of patients with a final diagnosis of osteomyelitis, osteomyelitis or septic arthritis, cellulitis or pyomyositis, and noninfectious conditions, they stated.
A total of nine patients had a final diagnosis of osteomyelitis, and “objective MRI criteria were present in all nine patients,” the authors wrote, while none of the remaining 25 patients had characteristic imaging features of osteomyelitis. Among the patients with an osteomyelitis diagnosis, “eight of nine had one or more imaging criteria of osteomyelitis, including intraosseous abscess, cortical breach, or subperiosteal abscess,” they said. The ninth subject was diagnosed with acetabular osteomyelitis based on evidence of marrow and soft-tissue edema in the obturator internus muscle, away from the intervention site.
The findings suggest that musculoskeletal MRI “plays an important role in the management of these patients because of its ability to evaluate underlying osteomyelitis despite recent intervention,” according to the authors. With correct clinical and surgical history, they wrote, “patterns of soft-tissue and marrow edema can be explained.”
Though intervention-related iatrogenic changes do not affect MRI's diagnostic efficacy in suspected osteomyelitis or septic arthritis, “MRI before intervention adds efficacy to patient management, guides the surgical procedure, and prevents additional surgery in children with suspected pelvic or appendicular osteomyelitis or septic arthritis,” the authors concluded.
Right foot after IV administration of gadolinium shows large soft-tissue abscess (arrows) and intraosseous calcaneal abscess (arrowhead).
T2-weighted humerus, intramedullary, and subperiosteal abscess (arrows).
Corresponding T1-weighted image of the distal humerus, shown above. Images courtesy Dr. J. Herman Kan