Imaging in pelvic osteomyelitis: support for early magnetic resonance imaging

BACKGROUND: Children with pelvic osteomyelitis may present with symptoms that are nonspecific. Conventional imaging modalities including plain radiographs, ultrasound, technetium bone scan, and computed tomography rarely demonstrate pathology that is diagnostic of this condition. As a result, accurate diagnosis is often delayed, and children may undergo surgical diagnostic or therapeutic procedures that may be avoided. We report the radiographic and magnetic resonance imaging (MRI) findings in 23 children admitted with a suspected diagnosis of pelvic osteomyelitis. We are presenting imaging findings in children with suspected pelvic osteomyelitis with emphasis on MRI abnormalities and to propose an anatomical classification based on the patterns of pelvic involvement. METHODS: The medical records and imaging reports of all patients admitted to our institution with a history and physical examination suggestive of pelvic osteomyelitis between July 31, 1992, and March 10, 2003 were reviewed. Criteria were defined for the diagnosis of pelvic osteomyelitis based on criteria used by Farley et al in 1985. Specific attention was paid to the imaging strategies used and the influence of each radiographic method on the ultimate diagnosis. RESULTS: Abnormalities on the MRI included soft tissue inflammation and bone edema. These findings were bright on T2 and short inversion time Short T1 inversion recovery (STIR) images and enhanced after gadolinium administration. Five distinct patterns of pelvic involvement were observed, each corresponding to a cartilaginous epiphysis or apophysis. These were the sacroiliac joint, triradiate cartilage, pubic symphysis, ischium, and iliac apophysis. One patient had a noninfectious cause of presentation with a deep vein thrombosis, whereas another was diagnosed with Hodgkin lymphoma in addition to osteomyelitis of the ischium. CONCLUSIONS: Magnetic resonance imaging is a sensitive technique for evaluation of pyogenic infections involving the pelvis. In patients presenting with clinical findings and laboratory studies suggesting an infectious process, MRI with gadolinium enhancement should be performed as an early study. Magnetic resonance imaging is also effective in identifying other conditions that may resemble pelvic osteomyelitis