OSTEOID OSTEOMA It is the commonest true benign tumour of the bone. Pathologically, it consists of a nidus of tangled arrays of paially mineralised osteoid trabeculae surrounded by dense sclerotic bone. Clinical presentation: The tumour is seen commonly between the ages of 5-25 years. The bones of the lower extremity are more commonly affected; tibia being the commonest. The tumour is generally located in the diaphysis of long bones. The presenting complaint is a nagging pain, worst at night, and is relieved by salicylates. There are minimal or no clinical signs, except for mild tenderness at the site of the lesion, and a palpable swelling if it is a superficial lesion. Diagnosis: It is generally confirmed on X-ray. The tumour is visible as a zone of sclerosis surrounding a radiolucent nidus, usually less than 1 cm in size. In some cases, the nidus may not be seen on a plain X-ray because of extensive surrounding sclerosis, and may be detected on a CT scan. Treatment: Complete excision of the nidus along with the sclerotic bone is done. Prognosis is good. It is not a pre-malignant condition. Reference: Maheshwari; Essential Ohopaedics 9th ed; Page no:235