Adamantinoma

DISCUSSION: The clinical history and figures are consistent with a diagnosis of adamantinoma. This is best treated initially by en bloc resection with wide margins followed by appropriate reconstruction to prevent local recurrence or metastasis.

Differentiating between adamantinoma (AD) and osteofibrous dysplasia (OFD) can be difficult, as the two lesion share many similar characteristics. AD is a rare, low-grade malignant primary bone tumor that occurs most often in the tibia and/or fibula of adolescent persons and young adults; however, it has been reported in other long bones, as well. Histologically, AD is composed of islands of epithelial cells in a spindle-cell stroma and nuclear atypia with mitotic figures may be present as well. OFD is a rare, benign, fibro-osseous lesion that typically is seen within the cortex of the tibia in children. Microscopically, OFD is characterized by a loose, often storiform fibrous background containing spicules of woven bony trabeculae that are lined by a layer of osteoblasts. Treatment of OFD in children usually consists of observation.

Kashima et al. assessed expression of podoplanin, a glycoprotein found in osteocytes, in OFD and AD as well as in fibrous dysplasia and metastatic cancer. Podoplanin expression was found in OFD and AD only, and the authors concluded that expression of podoplanin in an osteolytic tumour of the tibia may be useful as a diagnostic discriminant in distinguishing OFD from fibrous dysplasia and ALB from metastatic adenocarcinoma.

Most et al. completed a review article discussing the features associated with OFD and AD. They state that management of OFD varies from observation to surgical intervention, depending on the age of the patient and the extent of the lesion. Management of AD requires surgical resection with wide margins, followed by appropriate reconstruction, to minimize the risk of local recurrence or metastasis.

Figure A shows a lateral radiograph of a tibia with multifocal lytic lesions and areas of intervening sclerosis, which can give a “soap bubble” appearance. Figures B and C show the characteristic histological findings of AD including islands and cords of basaloid epithelial cells in a fibrous stroma with nuclear atipias and mitotic figures.

Illustration A shows an example of OFD for comparison. Note the classic intracortical anterior tibial lesion which is well marginated and surrounded by an area of sclerosis. Illustration B demonstrates the histology of OFD, showing a loose, storiform fibrous background containing spicules of woven bony trabeculae that are lined by a layer of osteoblasts.

Incorrect Answers:
Answer 1: Observation would be appropriate for a diagnosis of OFD in a child.
Answer 2: Radiation and chemotherapy are not effective treatments for adamantinoma.
Answer 3: Bracing would be appropriate treatment for OFD in the setting of tibial bowing or pending pathologic fracture.
Answer 4: Above the knee amputation would be appropriate as a salvage operation if en bloc resection and reconstruction failed.

DISCUSSION: The history, location, radiographs, and histology slide are all consistent with a diagnosis of adamantinoma - a low grade malignant bone tumor, most commonly found in the tibia after a very indolent course. The association of adamantinoma with osteofibrous dysplasia is a controversial one. Many believe they are a continuum of the same disease process, while others believe they are two separate diagnoses.

The radiographic features including the tumor location in the anterior tibial cortex with associated erosion of the anterior tibial cortex on advanced imaging, and the malignant histopathology slide make the diagnosis of adamantinoma from osteofibrous dysplasia (note the mitosis in the histology slide at the arrow). Of note, this patient also has a distal fibular lesion which on biopsy was adamantinoma.

Most et al review osteofibrous dysplasia and adamantinoma, discussing the diagnosis, treatment, and outcome. While adamantinoma is predominantly found in the tibia, several case reports of fibular and tarsal bone involvement have been reported in the literature.

Messerschmitt et al review the molecular diagnoses, presentation, treatment and outcome of osteosarcoma. While the local treatment for osteosarcoma has not changed significantly in recent years, the overall survival for osteosarcoma has significantly improved due to the use of chemotherapy for control of systemic disease.

Illustration A shows erosion of the anterior tibial cortex on computed tomography.

Incorrect Answers:
Answer 1: Osteofibrous dysplasia - this is the most difficult differentiator for this question. However, given the progression of disease, erosion of the tibial cortex, and malignant features of the histology section, the diagnosis of osteofibrous dysplasia isn't correct.
Answer 2: Chronic osteomyelitis - While the radiographs may be suggestive of osteomyelitis, the histology slide and advanced imaging showing erosion of the cortex aren't consistent with osteomyelitis.
Answer 4: Neither the radiographs nor the histology slide show any osteoid - a diagnostic necessity for osteosarcoma.
Answer 5: Fibrous dysplasia - again, neither the imaging nor the histology slide are consistent with fibrous dysplasia.

DISCUSSION: The patient has symptoms, radiographs, and histology consistent with an adamantinoma. Adamantinomas are rare tumors of long bones that can be mistaken for a carcinoma and other lesions such as myoepithelial tumor, malignant mixed tumor of bone, fibrous dysplasia/osteofibrous dysplasia, and vascular tumors. The histology often reveals epithelial islands with basaloid, spindle, and squamous features on a background of fibrotic stroma. The article by Desai is a study of 12 adamantinoma cases in which radiologically the tumor presented as a lytic, eccentric, intracortical lesion in the tibia. The histology revealed epithelial islands with basaloid, spindle, and squamous features on a background of fibrotic stroma. The article by McCaffrey analyzed 3 osteofibrous dysplasia patients because diagnosis and treatment are complicated by the fact that osteofibrous dysplasia can resemble monostotic fibrous dysplasia and adamantinoma of long bones grossly and microscopically and that it tends to recur if surgical intervention is performed before skeletal maturity is reached.