Adamantinoma is a rare bone tumor that arises most often in the lower limbs, especially the tibia. It is generally slow growing and of low malignant potential, but it can be locally aggressive and has risk of recurrence or metastasis under certain circumstances. Because an adamantinoma may infiltrate bone cortex and medullary cavity, careful diagnosis and surgical planning are critical to preserving limb function.
Histology and Biological Behavior
Adamantinoma is characterized by a biphasic cellular appearance: nests or islands of epithelial-type cells within a fibrous or osteofibrous stromal background. The epithelial component may form glandular or tubular structures, and occasionally cystic changes. The stroma is relatively bland, and mitotic activity is usually low.
The tumor grows gradually and may spread within the bone cortex, extend into the medullary canal, or erode into adjacent soft tissues. It may also produce skip lesions or satellite foci in the same bone. While metastasis is uncommon at presentation, it may occur later, especially to lungs or regional lymph nodes.
There is also a variant sometimes called osteofibrous dysplasia, like adamantinoma, which shares features with benign osteofibrous dysplasia but shows focal epithelial elements; this variant tends to be less aggressive but still requires vigilance.
Epidemiology
Adamantinoma is extremely rare, accounting for less than 1 percent of primary bone tumors. It typically presents in adults between ages 20 and 50, though younger and older cases have been reported. It affects males slightly more often than females. The tibia is the most frequent site, particularly in the anterior cortex or diaphysis, though involvement of the fibula or other long bones may occur.
Clinical Presentation
Symptoms
Because the tumor grows slowly, symptoms are often subtle and insidious. Patients may notice:
- Persistent or intermittent pain in the affected bone
- Swelling, fullness, or a palpable mass in the region
- A limp or altered gait, especially if structural weakening has occurred
- In some cases, a pathological fracture may be the first manifestation
Physical Findings
On examination, findings may include localized tenderness, mild swelling or deformity, and sometimes increased warmth over the lesion. In more advanced cases, soft tissue extension or cortical breakthrough may be palpable. Limb length or alignment may be affected if bony remodeling or bowing has occurred.
Because of the indolent nature, diagnosis may be delayed, sometimes for months or years.
Diagnostic Evaluation
Imaging
Initial imaging typically includes plain radiographs of the affected bone in two planes. Common radiographic features:
- Eccentric, lytic or mixed lytic-sclerotic lesion in the cortex, often with a “soap bubble” appearance
- Cortical thinning or expansion, possible endosteal scalloping
- Extension into medullary cavity or subtle endosteal changes
- Occasional periosteal reaction or soft tissue component
Computed tomography (CT) helps delineate cortical integrity, degree of bone destruction, and involvement of the medullary cavity. Magnetic resonance imaging (MRI) is valuable for assessing the extent of intramedullary disease, soft tissue extension, skip lesions, and planning surgical margins.
Bone scan or PET imaging may be employed to detect multifocality or distant spread.
Biopsy
Definitive diagnosis requires biopsy. Tissue sampling must capture both stromal and epithelial components and should be planned in consultation with the surgical team to avoid contaminating future resection planes. Histopathology and immunohistochemistry can confirm epithelial markers (such as cytokeratins) in the epithelial nests.
Because of overlap with osteofibrous dysplasia and other bone lesions, careful correlation of imaging and pathology is essential.
Treatment
Treatment is centered on surgical resection with adequate margins while preserving limb function where possible. The goals are complete removal of tumor, prevention of recurrence, and restoration of structural integrity.
Surgical Resection
Wide en bloc resection with negative margins is the mainstay. The extent of resection depends on tumor size, cortical involvement, medullary spread, and soft tissue extension. In many cases, limb-sparing surgery is feasible. Reconstruction of the segmental defect may be achieved by:
- Autograft (e.g. vascularized fibula)
- Allograft
- Endoprosthetic reconstruction
- Combination techniques
In cases where margins cannot be secured or limb salvage is contraindicated, amputation may be considered, though this is rare given modern reconstructive approaches.
Role of Adjuvant Therapy
Adamantinoma is relatively insensitive to radiation and conventional chemotherapy. Adjuvant therapy is generally reserved for metastatic disease or unresectable lesions, with limited efficacy.
Close follow-up and surveillance remain essential because of potential for late recurrence or metastasis.
Follow-Up, Prognosis and Complications
Prognosis
When complete resection with tumor-free margins is achieved, long-term outcomes are favorable. Ten-year survival rates are high. However, recurrence is a known risk, especially when margins are inadequate. If recurrence or metastasis occurs, management becomes more challenging.
Complications
Complications may include:
- Local recurrence
- Metastasis (especially to lungs)
- Graft failure, nonunion or fracture of reconstructive segments
- Loss of limb function or weakness
- Implant complications, infection
- Adjacent bone degeneration or stress fractures
Surveillance
Lifelong follow-up is recommended, with periodic imaging of the primary site and chest imaging to detect pulmonary metastasis. Early detection of recurrence increases the likelihood of salvage therapy success.
Differential Diagnoses
Important conditions to distinguish include:
- Osteofibrous dysplasia
- Fibrous dysplasia
- Eosinophilic granuloma
- Other primary bone tumors (e.g. chondrosarcoma, osteosarcoma)
- Benign bone cysts or bone infarcts
The presence of epithelial nests distinguishes adamantinoma from many mimics, but correlation with imaging and clinical features is critical.
Patient Education and Considerations
Patients should be counseled on the nature of adamantinoma, the importance of complete surgical resection, and the necessity of long-term follow-up. Rehabilitation, pain management, and functional support after surgery are key components of care. Given the rarity of the disease, management in specialized bone tumor centers with multidisciplinary teams is strongly advised.
References
Jain, D., Jain, V. K., Vasishta, R. K., Ranjan, P., & Kumar, Y. (2008). Adamantinoma: a clinicopathological review and update. Diagnostic pathology, 3(1), 8.
Kahn, L. B. (2003). Adamantinoma, osteofibrous dysplasia and differentiated adamantinoma. Skeletal radiology, 32(5), 245-258.
Smyth, S. L., Siddiqi, A., Athanasou, N., & Whitwell, D. (2023). Adamantinoma: a review of the current literature. Journal of Bone Oncology, 41, 100489.
