Cytological diagnosis of adamantinoma of long bone in a 78-year-old man.

A clinicohistopathological study of a rare case of adamantinoma of long bone in a 78-year-old patient is presented. The cytological features when evaluated in conjunction with clinical and radiologic features are sufficiently diagnostic. The primary knowledge of its existence and knowledge of its cytological features are important for a correct preoperative cytological diagnosis.

Introduction

Adamantinoma of long bone is a low-grade malignant tumor characterised by a variety of morphological patterns, most commonly epithelial cells surrounded by a relatively bland osteofibrous component and behaviorally by a tendency for local recurrence and the occasional development of lymph node and distant metastases, particularly to the lung.[1] It characteristically involves the tibia, but has also been reported in femur, ulna and fibula.[12] The majority occurs in patients in second or third decade of life.[3]

Case Report

A 78-year-old male patient presented with pain and swelling in the middle of left leg for the past 3 years. There was no history of fever, weight loss or other constitutional symptoms. Radiograph of the leg revealed a lytic, eccentrically located defect in the shaft of left tibia with sharply defined margins. There was no extension to the overlying soft tissue. Clinico-radiologically, a diagnosis of simple bone cyst was made. Considering the age of the patient, metastatic carcinoma was also kept in mind. However, routine investigations were within normal limits.

Fine needle aspiration cytology (FNAC) of the lesion was done using an 18-G needle and a provisional diagnosis of adamantinoma of tibia was made. En bloc excision was done and the patient was kept under follow-up. Till 1 year, there was no history of recurrence or metastasis.

Pathological findings

FNAC smears were highly cellular and showed few dispersed, benign appearing, spindle-shaped cells admixed with cohesive clusters of small, uniform ovoid to round epithelial cells. The latter had oval to round nuclei, mostly uniform with finely granular chromatin and inconspicuous nucleoli [Figure 1]. Histopathology showed solid nests of basaloid cells with peripheral palisading and sometimes a stellate configuration in the center. Immunohistochemistry confirmed the epithelial nature of the cells as they were positive for CK14 and 19.

Figure 1

FNAC smears showing cohesive clusters of small, uniform, ovoid to round epithelial cells (MGG, ×100)

Discussion

Adamantinoma of long bones characteristically involves the tibia.[2] and so was it in our case. It is usually seen in the second or third decade, whereas in our case the patient was 78 years old. Previous authors have described the cytological features of adamantinoma and a conclusive diagnosis can be reached with clinico-radiologic correlation.[45] Smears are highly cellular with multiple large clusters of cells, round to spindle-shaped, with round uniform nuclei, fine chromatin and scanty ill-defined cytoplasm, almost forming syncytium, mimicking basaloid squamous cell carcinoma. It is a bland epithelial tumor with no stroma at all.[4] Histopathology is however the gold standard. Correlation with clinical and radiologic findings usually prevents a misdiagnosis of metastatic carcinoma.[4] Further, the epithelial cells of adamantinoma do not appear anaplastic. Occasional examples of adamantinoma are composed entirely of spindle-shaped cells and histologically resemble fibrosarcoma. The characteristic clinical and radiographic features as well as lack of anaplasia, necrosis and significant mitotic activity preclude the latter diagnosis.[34] Electron microscopic and immunohistochemistry tests confirmed the epithelial nature of the tumor cells.[6] The keratins expressed are mainly 14, 19 and lesser of 5, 17, 7 and 13.[7] The prognosis is excellent if the lesion can be resected. However, pulmonary and lymph node metastasis can occur even after a long delay. Adamantinoma of long bone is a low-grade malignant neoplasm with no histological or radiographic features that allow reliable prediction of the clinical course. Factors associated with a more aggressive outcome include male sex, inadequate initial treatment, short duration of symptoms and pain. Initial treatment should consist of wide excision or amputation, and patients should undergo long-term follow-up for the development of recurrent or metastatic disease.[8] Our patient is still under follow-up with no history of recurrence.