OSTEOID OSTEOMA AND OSTEOBLASTOMA - MRI APPEARANCES AND THE SIGNIFICANCE OF RING ENHANCEMENT

We assessed the value of contrast-enhanced fat-suppressed MRI on nine patients with osteoid osteomas and osteoblastomas. The results were co mpared with plain films, bone scintigraphy, computed tomography (CT) a nd pathological specimens. On contrast-enhanced fat-suppressed T1-weig hted images the non-calcified nidi showed homogeneous enhancement, whe reas the calcified lesions showed a ring enhancement sign that was pro portional in intensity to the extent of the remaining part of the vasc ularized nidus. The degree of bone marrow and soft tissue enhancement was relative to the size and reactive inflammatory changes of the lesi ons. Although CT was diagnostic in most of the cases and more specific to show the calcified lesions, MRI was confirmatory in one case. We c oncluded that, although CT is the primary diagnostic investigation in osteoid osteomas, MRI can be reserved for equivocal cases.