Adamantinoma Imaging 

Adamantinoma is a rare tumor, and its origin remains controversial. Fischer first described the tumor in 1913,^[1] and since then, only approximately 200 cases have been reported. The tumor occurs almost exclusively in the long bones; tumors in the tibia account for more than 80% of cases. The diaphyseal region is the area most commonly affected. (See the images below.)

Adamantinomas are classified into 2 distinct types: classic and differentiated. Classic adamantinomas usually occur in patients older than 20 years, whereas differentiated adamantinomas occur almost exclusively in patients younger than 20 years. In addition, the 2 classifications of adamantinomas have distinct radiographic and histologic differences.

Patients with adamantinomas present with variable signs and symptoms; most commonly, they report pain and swelling. The tumor is slow growing, and patients may describe discomfort lasting months to years. Although ascertaining accurate mortality statistics is difficult because of the extremely rare nature of this tumor, the 10-year survival rate is believed to be 10%. Treatment options for adamantinoma are surgical and include either marginal or en bloc resection. Unfortunately, neither radiation therapy nor chemotherapy has been proven effective in the treatment of this insidious tumor.^{[2, 3, 4, 5]}

Preferred examination

Plain radiography, computed tomography (CT) scanning, and magnetic resonance imaging (MRI) may all be used to help assess suspected adamantinomous tumors. However, CT and MRI are not specific in the differentiation of this tumor from other conditions; findings often overlap with those of other tumors and tumor-like lesions. A variety of tumors and tumor-like lesions can mimic an adamantinoma. Histologic examination is key to the identification of an adamantinoma; the histologic features of these tumors have many variations.^{[6, 7]}

Limitations of techniques

Limitations of plain-film radiography include the relatively long list of differential diagnoses for adamantinoma. Many pathologic conditions that are as rare as or more common than adamantinoma demonstrate similar characteristics on plain radiographs, as well as CT scans and MRIs. This fact, coupled with the limited experience that most radiologists (and physicians in general) have in dealing with this tumor, makes the diagnosis and treatment of adamantinomas challenging.

In its early stages, an adamantinoma appears as an elongated, linear lucency on plain radiographs, and no periosteal reaction is noted in the surrounding bone. In later stages, cortical sclerosis becomes apparent on plain radiographs (see the image below).

The most common location is in the diaphyseal region of long bones, especially the tibia. A periosteal reaction and fracture are less common late-term sequelae of adamantinomas that can also be depicted on plain radiographs.

The differentiation of adamantinoma from fibrous dysplasia and osteofibrous dysplasia may be difficult by using plain radiographs alone. When questions arise in the diagnosis of the tumor, the histologic and clinical features must be included to narrow the differential diagnosis.

False positives/negatives

False-positive findings include fibrous dysplasia, osteofibrous dysplasia, fibroma (nonossifying or ossifying), bone cyst (aneurysmal or simple), chondrosarcoma, chondromyxoid fibroma, eosinophilic granuloma, and hemangioendothelioma.

Because of the extremely rare nature of this tumor, a list of false-negative findings has not been adequately formulated.

CT scans often are used to study adamantinomas, but the findings are not specific. CT scans of the lower extremity often reveal a hypoattenuating sclerotic region in the tibial diaphysis (see the image below).

False positives/negatives

False-positive findings include fibrous dysplasia, osteofibrous dysplasia, fibroma, bone cyst, and chondromyxoid fibroma.

MRI often is used to image adamantinomas, but the findings are nonspecific. When MRI is used to study adamantinomas, the tumors demonstrate low signal intensity on T1-weighted spin-echo images and high signal intensity on T2-weighted images. Because these appearances are also typical of most tumors, these findings are nonspecific.

False positives/negatives

False-positive findings include fibrous dysplasia, osteofibrous dysplasia, fibroma, bone cyst, and chondrosarcoma.

The use of nuclear medicine to study adamantinomas is a relatively new undertaking; therefore, few data regarding the tumors have been collected. However, the following findings are believed to correspond to adamantinomous lesions: increased blood flow in the region of the tumor, increased blood pooling, and increased accumulation of technetium-99m methylene diphosphate in the area of the tumor.