Giant cell tumours, [s8]rare

These unusual tumours form about 5% of all primary bone tumours; most arise de novo, and a few in Paget's disease of bone. The common sites are the epiphyses around the knee (femur, tibia and fibula 50%) the lower radius (15%), the pelvis and sacrum (12%), and the maxilla (26.7). They consist of giant cells (like osteoclasts) and fibroblasts, and are graded histologically as I (low grade), II (intermediate) and III (relatively malignant). First they expand the cortex, and then they spread through it. Lymphatic spread is rare, and distant metastases unusual, but local recurrence after inadequate excision is common.

GIANT CELL TUMOURS X-RAYS. Typically, there is an eccentric osteolytic lesion in the epiphysis which extends into the metaphysis in larger tumours, and has a ''soap bubble' appearance. There is usually little sclerosis of the cortex. A defect in it is a sign that the tumour has penetrated it. In small bones there are non- specific lytic lesions.

THE DIFFERENTIAL DIAGNOSIS includes a simple bone cyst, fibrous dysplasia, a chondroma, other bone tumours (primary and secondary), and the bone cysts of hyperparathryroidism. Confirm the diagnosis by biopsy.

THE PROGNOSIS is good because metastases may never occur. After total excision 70% of patients survive 35 years. After curettage the 5, 10, and 35 year survival rates are 45%, 40%, and 35%.

MANAGEMENT. If possible, refer the patient to an expert for total excision of his lesion, and grafting of the gap; he may need an arthrodesis of his knee. If you cannot refer him, excise the appropriate area of cortex under a tourniquet, and curette the lesion. This is far from ideal, because local recurrence afterwards is common, and makes curative surgery thereafter difficult. Avoid curetting, if you can, because the prognosis after a total excision is so good. Avoid amputation, except for recurrent disease which cannot be totally resected.