Adamantinoma

Adamantinomas are rare indolent malignant bone tumours with a predilection for the tibial diaphysis. Following excision, local recurrence can be problematic and may occur after an interval of decades. Lymphadenopathy and metastases complicate <30% of cases ¹².

Terminology

Ameloblastomas, which are benign locally aggressive bone tumours of the mandible, were previously also known as adamantinomas of the mandible. Although the histology is similar, a common histogenesis is unproven.

Epidemiology

Adamantinomas account for <1% of primary bone tumours and typically present between the 2^nd and 5^th decades. There is a slight male predilection (M:F = 5:4) ¹².

Clinical presentation

Symptoms of pain, swelling and tibial bowing deformity are slowly progressive. Pathological fracture presents acutely.

A history of prior local trauma may be elicited in around 60%. Paraneoplastic severe hypercalcaemia with coma and pancreatitis have been reported ¹².

Almost all cases occur in long bones and up to 85% occur in the mid tibial shaft. Some occur in the tibial metaphysis and up to 15% concurrently involve the fibula. Occasionally tumours arise in the fibula alone, the humerus, hand, foot, radius, femur, ribs, spine, facial bones andor pretibial soft-tissues are involved ¹².

Pathology

The histogenesis remains the subject of debate. The histology is heterogeneous and epithelial, synovial, endothelial and osseofibrous components have been demonstrated. Transformation of osseofibrous dysplasia or angioblastic derivation have been proposed. Extensive sampling of the most radiolucent areas is recommended for diagnosis ¹².

Subtypes are distinguished by degree of differentiation, osseofibrous component, Ewing’s sarcoma-like components or areas of squamous cell carcinoma ¹².

Tumours are positive for cytokeratins 5, 14 and 19, and the stromal component is positive for vimentin.

Radiographic features

The tumour is typically well-circumscribed, expansile and multiloculated with a thin sclerotic rim and involves the anterior tibial diaphyseal cortex. It can spread into the medullary canal and soft-tissues. There may be multiple tumour nodules and concurrent involvement of the fibula.

Plain radiograph / CT

Typically, it appears as a multilocular or slightly expansile osteolytic cortical lesion. This may be visualised as areas of lysis interspersed with areas of sclerosis ³. Lesions tend to have an eccentric epicentre ⁴ and a lack of periosteal reaction. Tumours may be locally aggressive disease at presentation.

MRI

MRI is essential to define disease extent pre-operatively. The disease may be unifocal or present as multiple nodules.

• solitary lobulated focus 

• multiple small nodules in onemultinodular with skip lesions or more foci periosteal involvement.

In some patients separated tumour foci may be seen, defined as foci ofTumour demonstrates high signal intensity on either T2- or contrast-enhanced T1-weighted images, interspersed with normal-appearing cortical or cancellous bone ². A fluid-fluid level may occasionally be seen.

FDG PET-CT

Lesions are FDG aavid.

Treatment and prognosis

Surgical en bloc resection with wide margins and subsequent reconstruction is preferred. Amputation is sometimes necessary particularly for local recurrence. Curettage should be avoided due to a high incidence of local recurrence.

Local recurrence has been described up to 36 years post resection and metastases occur in 15-30% of patients affecting lymph nodes, lungs, bone, liver, other abdominal viscera, retroperitoneum and pericardium.

10-year survival may be as high as 92% and recurrence-free survival approximately 72%. The optimal duration and frequency of follow-up has not been defined.

History and etymology

Adamantinoma is derived from the Greek word "adamantinos", which means "very hard". It was first observed in the shaft of an ulna in 1900 by C Maier ⁸, who believed it was a carcinoma, although the term "adamantinoma" was coined by B Fisher in 1913 ⁹.

Differential diagnosis

Imaging differential considerations include ⁶:

• chondromyxoid fibroma

• fibrous dysplasia

• osteofibrous dysplasia: has a more ground-glass texture on CT