Clinical History
Local swelling and pain in her left shin.
Imaging Findings
The patient presented with swelling in her left shin and occasional pain for 3 years. Physical examination revealed a tender mass of 10 cm in the anterior aspect of the lower leg.
Plain films showed an intramedullar predominantly osteolytic lesion involving the middle third of the tibial diaphysis. The lesion was sharply delineated and slightly expansile. Reactive bone sclerosis and small satellite radiolucent foci were also noted.
At MRI study the lesion exhibited homogeneous intermediate signal intensity on T1-weighted images and high signal intensity on T2-weighted images and STIR. This study ruled out the presence of skip lesions or soft-tissue infiltration.
A body-CT did not disclose any abnormality. Then, wide en bloc excision of the involved segment with interposition of an allograft was performed. There were no signs of metastasis or recurrence at 8-year follow-up.
Discussion
Adamantinoma is an extremely rare, locally aggressive or malignant neoplasm which origin remains controversial. It has a slight male predominance and although it has been seen in a wide age range, most occur between the ages of 20 and 50 years. Patients typically present with local swelling with or without accompanying pain for months to years. It occurs almost exclusively in the long tubular bones (97% of cases) with a characteristic predilection for the tibia (80-85% of cases) and a particular propensity for the middle third of the tibial diaphysis.
On plain-film radiography, adamantinoma appears as a central or eccentric, multilocular, slightly expansile, sharply or poorly marginated lytic lesion. Satellite lesions in direct continuity with the major lesion are not uncommon and reactive bone sclerosis and bowing deformity of the tibia may be found. Periosteal reaction is not present in the absence of a pathologic fracture. CT and MRI findings are not specific, but MRI plays an important role in preoperative planning.
Histologically, this tumor presents a wide range of morphologic patterns, not only among patients but also among different areas of the same tumor. Four basic patterns are found in varying combinations: basaloid, squamous, spindle and tubular. A subgroup called “differentiated adamantinoma” with different radiologic, histologic and clinical features has been described in patients younger than 20 years with a purely intracortical location.
Differentiation between adamantinoma and fibrous dysplasia may be difficult, both radiographically and pathologically. A ground-glass appearance with intralesional calcifications suggests fibrous dysplasia whereas the presence of small satellite radiolucent foci is more characteristic of adamantinoma.
Other differential diagnoses include osteofibrous dysplasia and non-ossifying fibroma. Adamantinomas with more aggressive behaviour may resemble metastasis or osteosarcoma.
Wide en-bloc resection is the recommended treatment because it generally prevents local recurrence. Adamantinoma has the potential to metastasize (15-20%), commonly to the lung, bone and lymph nodes, even years after the initial therapy. The 10-year survival rate is estimated to be approximately 10%.
Differential Diagnosis List
Adamantinoma of the tibia
Final Diagnosis
Adamantinoma of the tibia
