MRI of adamantinoma of long bones in correlation with histopathology

The purposes of this retrospective study were to assess specific MRI features of adamantinoma, including classic adamantinoma and its osteofibrous dysplasia-like variant, and to assess the role of adamantinoma in surgical planning.

MR images of 22 patients with histologically proven adamantinoma, subtyped according to defined criteria, were analyzed, with emphasis on morphologic features, signal intensities, and enhancement parameters. Intra- and extraosseous tumor extent was determined. In all patients, examination of the corresponding resected specimens was performed with regard to tumor extent and presence of multicentricity. Moreover, radiographs were reviewed, and radiographic features derived from the literature were determined.

All tumors were primarily localized in the tibia diaphysis (including one patient with additional lesions in the fibula), most frequently in the anterior cortical bone (19/22) with extension toward the bone marrow in 12 patients. We distinguished two morphologic patterns: a solitary lobulated focus versus a pattern of multiple small nodules in one or more foci. Separated tumor foci, defined as foci of high signal intensity on either T2-weighted images or T1-weighted contrast-enhanced images, interspersed with normal-appearing cortical or spongious bone were seen in six patients. All tumors showed intense and homogeneous static enhancement, but there was no uniform dynamic enhancement pattern. No relationship between MRI features and histologic subtype of adamantinoma was found.

Some uniform MRI characteristics, along with those of radiography, may contribute to the diagnosis of adamantinoma; however, these are not related to the histologic subtype. MRI is pivotal for precise locoregional staging, especially for depiction of distant cortical foci, soft tissue, and intramedullary extension and thus is useful for determining tumor-free margins and strategies for reconstructive surgery.