# Diagnostic Radiology/Musculoskeletal Imaging/Tumors Basic/Adamantinoma

Adamantinoma of Long Bone (extragnathic adamantinoma): Adamantinoma is a rare primary low-grade malignant tumor of bone that is locally aggressive. Adamantinoma of the long bone is not related to adamantinoma or ameloblastoma of the mandible and maxilla, which is derived from Rathke's pouch.

## Demographics

* Age: 10 - 50 (50% are age 10 to 30)
* Sex: Males greater than or equal to females
* Site: ~80% involve tibial diaphysis (some with anterior cortical involvement). Other bones that may be involved are the humerus, ulna, femur, fibula and radius. Rare in other tubular bones.

## Clinical Presentation

Approximately 60% of patients with adamantinoma have a history of trauma, including fractures, to the affected bone, but it is unclear whether trauma is involved with formation of the tumor or the formation of the tumor leaves the bone weak and susceptible to injury.
Common symptoms (duration from a few weeks to years):
* Localized, insidious aching pain
* Gradual swelling and deformity of the affected limb
* Limping
* Increased pain with activity or lifting
* Advanced or recurrent lesions may be associated with a soft-tissue mass (15%)

## Imaging Findings

Conventional Radiographs: (Here is an example from BrighamRad)
* Eccentrically-located
* Well-circumscribed
* Slightly expansile
* Multilocular
* Osteolytic with intervening reactive sclerosis ("soap-bubble")
* Cortical thinning
* Little or no periosteal reaction (Unless the lesions extends through cortex to the soft tissue)
* Late stages result in bone deformation (e.g., bowing of the tibia)
* Computed Tomography:
** Low attenuation expansile mass with sclerotic margins
** Superficial erosion and soft tissue involvement
* Magnetic Resonance Imaging:
** MRI findings in adamantinoma are non-specific, but can help demonstrate intraosseous and extrasseous involvement.
** T1-weighted
*** Low signal intensity
*** Peripheral enhancement of the lesion when post-gadolinium (Here is an example from BrighamRad)
** T2-weighted
*** High signal intensity that does not diminish with fat suppression technique
*** Decreased signal in the periphery of the lesion, consistent with sclerosis
** STIR (Here is an example from BrighamRad)
*** Increased signal in the region corresponding to the lytic lesion on plain films
*** Decreased signal in the periphery of the lesion, consistent with sclerotic changes
* Bone Scan (Tc-99m MDP):
** The pattern of increased isotope uptake on flow, pool, and delayed images corresponds closely to the radiographic extent of the lesion

## Pathology

* Gross Pathology
** Firm, rubbery, grayish-white to yellow with smooth to lobulated external contours
** Involvement of the cortex and periosteum is common
** Cystic degeneration is common
** Foci of hemorrhage are common
** Eccentrically located and sparing the medullary cavity
* Microscopic histology:
** There are two distinctly different components:
** Epithelial origin composed of squamous cells and epithelial pearls
** Mesenchymal origin composed of immature mesenchymal cells and spicules of dysplastic bone

## Differential Diagnosis

* Giant cell tumor
* Fibrous dysplasia
* Simple bone cyst
* Aneurysmal bone cyst (ABC)
* Eosinophilic granuloma
* Osteomyelitis
* Osteofibrous dysplasia (ossifying fibroma)
* Chondromyxoid fibroma
* Chondrosarcoma
The radiographic features of adamantinoma and osteofibrous dysplasia of the tibia are generally identical.
Adamantinoma, fibrous dysplasia and osteofibrous dysplasia (ossifying fibroma) share many radiographic and pathological features, but their interrelationships are unclear. Sarisozen et al. state that there is an entity known as osteofibrous dyplasia-like adamantinoma (differentiated adamantinoma) that may be a precursor to classic adamantinoma.

## Natural History

Adamantinoma usually presents as an intraosseous, intracortical stage I-A sarcoma.
This low-grade, slowly-growing malignancy metastasizes in about 20 percent of cases by both hematogenous and lymphatic routes to other parts of the body, usually to the lungs or nearby lymph nodes. Of these cases, about 15 percent of the patients die.
Young females seem to be at the highest risk for early demise with the average age of death being 33 years compared to 48 years for men.

## Treatment

Treatment of adamantinoma is wide surgical excision - neither radiation therapy or chemotherapy is effective. Local recurrence is common if the tumor is not completely removed. Filippou et al. report a case of recurrent adamantinoma with metastasis to the lungs that was successfully retreated with surgical resection of the recurrent tumor and metastases.

## References

* Adamantinoma by Rahul Patel, M.D., University of Washington Department of Radiology