ChristinaGutowski

Adamantinomais a rare, low-grade malignancy of bone with mesenchymal and epithelioidfeatures. Adamantinoma almost always occurs in the diaphysis of the tibia (morethan 90% of cases). Adamantinoma is slow-growing and is characterized clinicallyby the gradual development of pain and swelling at the tumor site in youngadults. Radiographically, adamantinoma resembles osteofibrous dysplasia (alsoknown as cortical fibrous dysplasia), a benign bone lesion of the tibia inpediatric patients.

Epidemiology

Adamantinomais an extremely rare bone tumor, accounting for 0.1-0.5% of all malignant bonetumors. Adamantinoma is slightly more common in males and tends to develop inpatients 20-40 years old.

ClinicalFeatures

Adamantinomamost commonly develops in the anterior cortex of the tibial diaphysis, leadingto swelling and deformity of the tibial crest with progressive pain. Adamantinomaoccasionally presents as pathologic fracture. Adamantinoma can be confused withfibrous dysplasia of the tibia, which must be distinguished by a high index ofclinical suspicion and appropriate biopsy. In pediatric patients, osteofibrousdysplasia presents similarly to adamantinoma.

RadiologicFeatures

Onradiographs, adamantinoma displays a classic multicystic, “soap-bubbly” appearance along the anterior tibial cortex, characterized by mixed lytic and scleroticregions. The average length of the lesion is approximately 10 cm. Radiographsmay reveal bowing of the tibia due to chronic bone remodeling, and an extraosseoussoft-tissue mass (Figure 1).

Figure1. Lateral X-ray of adamantinoma of the tibia, demonstrating a mixedlytic/sclerotic lesion with a soap-bubbly appearance. The anterior cortex isdestroyed, and a bowing deformity is present.

On computedtomography (CT) scans, adamantinomas are characterized by corticalthinning and reactive sclerosis. There may frank cortical disruption, soft-tissuemasses, and involvement of the medullary canal.

Magneticresonance imaging (MRI) will demonstrate cortical thinning, expansion, andmarrow replacement on T1 sequences. Fluid-sensitive sequences will demonstrateareas of cyst formation, which can be blood-filled and lead to fluid-fluidlevels, as well as perilesional or intralesional edema (Figure 2). Adamantinomasenhance with contrast.

Figure2. Sagittal short tau inversion recovery MRI of adamantinoma of the tibia,demonstrating an anterior soft-tissue mass, cortical destruction, andfluid-fluid levels within the cystic component.

Pathology

Grossly,adamantinoma is a rubbery, well-defined tumor that may contain areas of cystformation and hemorrhage. The tumor is predominantly intracortical, although expansionboth out of bone and into the intramedullary space are common.

Microscopically,the defining feature of adamantinoma is a biphasic pattern of bland spindlecells and epithelioid cells. The spindle cells are found in a fibrous stromawhich stains positively for vimentin; the epithelioid cells are found in nests which stain positively for cytokeratin. The epithelial component is thought torepresent the primary neoplastic cell population, which in turn stimulatesreactive fibrous growth and cortical thinning (Figure 3).

Figure3. H&E stain of adamantinoma, demonstrating bland spindle cell stromasurrounding nests of epithelioid cells.

Instudies of adamantinoma pulmonary metastasis, only the cytokeratin-positive,epithelial-cell population was present in the nodules.

DifferentialDiagnosis

Theradiographic appearance of adamantinoma of the tibia can be confused with thatof osteofibrous dysplasia, fibrous dysplasia, and osteomyelitis, an intracorticalabscess or osteosarcoma. Histologically, the epithelial cells of adamantinoma canbe misdiagnosed as metastatic carcinoma, although a recent finding that the epithelialcells are uniformly positive for keratin 14 and keratin 19 can assist in the correctdiagnosis. The spindle cells of adamantinoma can be misdiagnosed as primarybone sarcoma especially if epithelial cells are not seen.

DiseaseCourse: Treatment and Prognosis

Adamantinomais typically treated with surgery. Wide en bloc excision of the lesion isnecessary to achieve durable local control. Reconstruction is based on the sizeand location of the lesion and may involve an endoprosthesis, bulk allograft,autograft, alloprosthetic composite, or distraction osteosynthesis (Figure 4).Chemotherapy is not indicated due to the low-grade nature of this tumor, andradiation has not proven useful for treating either primary or recurrentdisease.

Localrecurrence after wide excision occurs in up to 15% of cases and is thought tobe due to satellite lesions that exist beyond the primary tumor mass.Metastasis occurs in up to 20% of cases, oftentimes many years after amargin-negative excision.

Figure4. (Left) AP and (right) lateral X-ray demonstrating intercalary endoprostheticreconstruction of the tibia after wide excision of adamantinoma.

Long-termsurveillance is necessary for both local and distant recurrences. The meanduration to local recurrence has been reported at 5 to 15 years aftertreatment; distant recurrences have been reported at even 20 yearspost-operatively. Local recurrences are treated surgically, with overall limbsalvage rates of approximately 70%.

CommonlyTested on Exam

1. Classic appearance and location on X-ray
2. Biphasic histologic characteristics, with cytokeratin-positive, epithelial cell nests
3. Surgical treatment with wide excision, no chemotherapy or radiation