INTRODUCTION:

Adamantinoma is low grade malignant tumor of fibroblast origin. Also called as primary epidermoid carcinoma of bone, malignant angioblastoma or epithelial tumor of bone. It was first described by Fischer in 1913.¹ It represents less than 0.4% of all malignant bone tumors.² The exact origin of adamantinoma is unknown, the classic variant is composed of epithelial cells and osteofibrous components. It is more prevalent in men than in women, ratio being 5:4. The common age of presentation is in the second decade, though it can vary greatly between the second to fifth decades.³ The common site of occurrence is the ramus of the mandible. The other uncommon locations include shaft of long bones (97%), mid-shaft of tibia (80%-85%).⁴ Other rare locations includes the humerus, ulna, femur, fibula and radius but ribs, spine, metatarsal and carpal bones.⁵ The characteristic features of adamantinoma is slow, gradual development with high chances of local recurrences and also metastases to lungs.⁶ In this case study, we have presented a rare histological acanthomatous variant of adamantinoma of the right tibia with metastases to the right inguinal region.

CASE REPORT:

A 45 year old male patient presented with history of pain in right leg since 3-4 months, insidious onset, gradually progressive, aggravated on exercise, relieved on rest and medication. Later patient had no relief on medication. There was no history of trauma or fall preceeding to onset of symptoms. The patient also complained of swelling in the right groin since 1 month, without pain. On examination, the patient was stable. Local examination showed, a swelling of about 5X3cm in the upper end right leg, tender, well defined, hard in consistency, smooth surface, involving the right knee joint line. There was restriction of movement, but range of movements was present. Examination of right inguinal region revealed a 7X6cm firm, non-matted mass, immobile, non-tender, non-reducible, non-pulsatile mass. Local examination of penis, scrotum, anal canal, hernia orifices was normal. Baseline investigations were done, all the haematological parameters were normal, ultrasound abdomen and chest radiograph was normal. Plain radiograph of right tibia showed large central lytic lesion with sclerotic margins, involving the upper end and shaft of tibia without involvement of right knee joint. Supra-patellar amputation of right leg with right inguinal and right external iliac nodal dissection was done. Histopathological examination of the mass was done. The reported was suggestive of acanthomatous adamantionoma. The features are as described, central area of squamous cell nests which were well differentiated with keratinization surrounded by a rim of myxoid cells. Further immunohistochemistry(IHC) study was done to confirm the diagnosis. IHC was also consistent with the diagnosis and confirmed the diagnosis. Positivity was found for cytokeratin(CK), EMA, CK-19, CK-5, CK-6, P-63, and Ki-67 and vimentin. Also metastases to right inguinal lymph node was confirmed.

DISCUSSION:

The first bone tumor with epithelial characteristic was reported by Maier in 1900, later in 1913 Fischer termed it as adamantinoma. It is more common in men than in women. The age of presentation varies between the second to fifth decade. The uncommon sites includes the shaft of long bones(97%), of which the mid-shaft of tibia being the most common site(80-85%). The symptoms at presentation include pain with localised swelling. Swelling is the most common symptom. Pain may be present due to history of repetitive trauma associated with adamantinoma.⁷ Adamantinoma is low grade malignant tumor, and can metastasize to loco-regional nodal areas and to lungs at presentation. The patient in the case report was also a middle aged man in the fifth decade with pain and swelling in the right tibia since 3-4 months and swelling in the right groin.

Three theories have been proposed for the source of cell of origin, 1) epithelial, 2) angioblasts, and 3) synovial tumors from uncommon ectopic sites. This was done because the tumor tissue is composed of both epithelial and osteofibrous components.⁸ In different combinations, different patterns are formed. On microscopy, the commonest form is the classical variant, followed by the osteofibrous pattern. In the classic variant, the types are basaloid, spindle cell, tubular, and squamous patterns. In the classical variant, central epithelial component with surrounding zone of fibrous tissue containing few immature trabecuated bone components are seen. In the osteofibrous variant, cental area of fibrous tissue, surrounded by peripheral zone of epithelial components are seen. Spindle cell variant is most commonly seen with recurrent lesion and metastatic lesions. The typical findings of classical variant were consistent in our case as well, which showed a well differentiated keratinizing pattern of squamous cell nests surrounded by a rim of myxoid cells.

Immunohistochemistry exhibits positivity for both epithelial and osseous elements. Fibrous components are positive for vimentin. Epithelial components show positivity for cytokeratin(CK) 5, 14, 19; rarely positive for CK 1,13,17. It is usually negative for CK 8 and 18. Also shows positivity for epithelial growth factor, fibroblast growth factor, fibroblast growth factor receptor. Our case had features as described, also positivity was found for p-63, Ki-67 and CK-6, which favour our diagnosis of acantomatous adamantinoma.

Genetic studies reveal chromosomal abberations on chr 7,8,12,19.⁹ Also aneuploidy has been associated with epithelial components.¹⁰ There is loss of heterozygosity of p53 gene. Rarely,(11;22) translocations have been reported in case of adamantinoma, and is termed adamantinoma-like ewing^’s sarcoma.¹¹ 11;22 translocation is not seen is in adamantinoma.

Radiological investigations include radiographs, computer tomography(CT), magnetic resonace imaging(MRI). All the modalities are necessary not only to confirm the diagnosis, also to define the extent of involve and the aggressiveness of the tumor. On plain radiographs usually eccentric, lobulated, cental lytic lesions with a peripheral sclerosis is present in the diaphyseal or metaphyseal ends of long bones. These lesion tend to appear on tibia with a typical picture of soap-bubble appearance.¹² CT shows osteolytic lesion in the bone. MRI is the investigation of choice. It helps not only in defining the extent of cortical involvement of bone, soft tissue involvement, but also helps in ruling out other etiologies such as ewing^’s sarcoma, adamantinoma, osteosarcoma, metastatic disease, fibrous dysplasia of bone.¹³ The typical features as described in the literature was true in our case as well.

Treatment of adamantinoma has no definitive guidelines. Excisional biopsy is preferred rather than curratage of bone. Curratage of bone is associated with recurrence’s, upto 30% recurrence has been reported with curettage.¹⁴ Radical excision of the bone is associated with better outcome and prognosis. Limb salvage procedures include en-block resection, followed by reconstruction of the bony defect which includes vascularised or non-vascularised bone grafts, custom made protheses, intercalary allografts and distraction osteogenesis.¹⁵ When limb salvage is not possible, amputation is the definitive treatment of choice. The incidence of mortality with adamantinoma is about 17%, and increases to about 20% when pulmonary metastasis is present. In our patient work up was done and right supra patellar amputation was done, with right inguinal and right external iliac lymph nodal dissection was done and histopathological examination further showed metastases to right inguinal region.