Related case: Bone lesion 1

CLINICAL FEATURES

• Rare, primary low-grade malignant tumor of bone composed of epithelial cells and a fibrous or osteofibrous stroma;

• Age:  mostly adolescents and young adults, mean age 32.9 years. Males greater than or equal to females;

• Site: the tibia is involved almost exclusively (~90%). Other bones that may be involved are the humerus, ulna, radius, femur and fibula.

• Frequency: less than 1% of malignant primary bone tumors;

• Clinical presentations: 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;

• Approximately 60% of patients 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;

• Metastasize to lung and local lymph nodes in 15-20% of cases.

RADIOGRAPHIC FINDINGS

• Multiple, sharply circumscribed, lucent zones within the cortex of the mid-portion of the tibia;

• Eccentrically-located, osteolytic with intervening reactive sclerosis ("soap-bubble")

• Slightly expansile, 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)

GROSS FINDINGS

• Soft to firm, gray-white tumor located in the cortex and form lobulated masses. The tumor may extend into the medullary cavity.

MICROSCOPIC FINDINGS

• Always show epithelial differentiation with variable histologic appearances:

  1. Basaloid or classic pattern: closely resembles ameloblastoma. Consists of nests or larger masses of cells with peripheral palisading of tumor cells. The central cells are small, spindled, and have uniform nuclei without significant atypia. There may be some microcystic changes;

  2. Spindle cell pattern: similar to the basaloid pattern except for the lack of palisading cells at the periphery. The cells may occur in islands merging into a hypocellular spindle cell stroma or the entire lesion may be spindled. This pattern is similar to the monophasic synovial sarcoma;

  3. Tubular pattern: clusters of small epithelial cells form tubular structures in a fibrous stroma. Occasionally, the epithelial cells line sinusoidal spaces, resembling a vascular neoplasm;

  4. Squamous pattern: this is seen within the basaloid pattern, in which individual cells show cytoplasmic keratinization or have the appearance of prickle cells. Keratin pearls are seen, but rarely.

• Lack of marked cytological atypia in all patterns. Fibrous dysplasia or osteofibrous dysplasia-like areas are frequently seen.

SUBTYPES

DIFFERENTIAL DIAGNOSES

• Metastatic carcinoma: in most cases, the location in the tibia and the relatively young age of the patients should suggest a diagnosis of adamantinoma. Metastatic carcinomas usually have more cytologic atypia.

• Fibrosarcoma: the adamantinoma with a purely spindle cell pattern may be mistaken for fibrosarcoma. Unlike fibrosarcomas, adamantinomas do not form collagen.

• Synovial sarcoma: identical to adamantinoma with a spindle cell pattern. However, knowing that the tumor is a primary bone tumor should prevent mistaking it for synovial sarcoma.

IMMUNOHISTOCHEMISTRY AND SPECIAL STAINS

• The epithelial cells are positive for cytokeratin, while the stromal showed positivity for vimentin;

• The epithelial cells are negative for Factor VIII;

• The epithelial cells are negative for cytokeratins 8 and 18 that are usually present in synovial sarcoma and metastati carcinoma.

ELECTRON MICROSCOPIC FINDINGS

• Evidence of epithelial cells.

CYTOGENETIC STUDIES

• Recurrent extra copies of chromosomes 7, 8, 12, 19, and 21.

TREATMENT AND PROGNOSIS

• Locally aggressive, 10-year survival rate is estimated to be approximately 10%;

• Treatment options are surgical and include either marginal or en bloc resection;

• Neither radiation therapy nor chemotherapy has been proven effective.

REFERENCES

• Clinicopathological features, diagnosis, and treatment of adamantinoma of the long bones. Orthopedics. 2007 Mar;30(3):211-5

• AFIP, tumor of the bone and joints, series 4.