Osteoid osteoma: Radiofrequency ablation

A 24-year-old male patient first presented to the orthopaedic OPD with complaints of right hip pain for the past year which had aggravated for the past 11 days. The patient was limping because of the pain. There was no history of trauma.

Plain radiography showed no definite abnormality. The patient showed no improvement in symptoms on follow up.
A non-contrast CT pelvis was planned to rule out any underlying cause of pain. Non-contrast scan of the pelvis showed a well-defined cortical lytic lesion with a dense sclerotic rim, close to the lesser trochanter placed anteriorly in the metaphyseal region. The lesion had a narrow zone of transition. A calcific nidus was seen within the lesion. The findings were suggestive of an osteiod osteoma. The patient was started on aspirin and showed improvement in symptoms. The patient declined a surgical treatment following which he was referred to the Interventional Radiology team. A radiofrequency ablation was planned using CT guidance. The cortex of the lesion was cored using a bone biopsy needle and an RF probe was placed within the nidus and ablation was performed. On follow up the patient was doing well and had no recurrence.

Osteiod osteoma is a benign bone tumor which was first described by Dr. Jaffe [1]. It constitutes 10% of all skeletal lesions [2]. The lesion is characterised by two zones, a central zone known as the nidus which is composed of atypical bone and the peripheral zone which is sclerotic and contains osteoclasts, osteoblasts and dilated capillaries. The lesion has a rich neural supply. The nidus has high levels of prostaglandins which is the cause of the painful nature and also the reason why aspirin reduces pain. The lesion usually measures less than 1.5 cm. The lesion is most commonly seen in the long bones of the lower limbs. On radiography the lesion appears as a central nidus which may be mildly calcified and surrounded by a sclerotic rim. Osteoid osteoma can be of three types: a) cortical, b) medullary and c) subperiosteal. CT shows similar characteristic features including low density nidus, sclerotic rim and varying degree of calcification within the nidus. CT is highly specific in detecting the nidus. MRI is used to assess the surrounding marrow and soft tissue changes associated with the lesion. Dynamic MRI shows early enhancement in arterial phase followed by early partial washout. This feature can also help differentiate a Brodies abscess which shows slow enhancement without any arterial peak enhancement.
Various treatment options include: conservative management, surgical management and percutaneous therapy. Surgical management was the only option available till the recent past and was associated with extensive resection leading to extensive tissue damage, limited mobility and complications.
Percutaneous treatment including radiofrequency ablation (RFA), percutaneous resection with alcohol ablation and laser ablation. RFA is an electrosurgical technique which uses high frequency alternating current. It is a widely used technique which allows image-guided precise heat delivery to the target tissue. Heat induces friction leading to coagulation necrosis. It is performed under spinal or general anaesthesia. A study has reported up to 96% technical success with the procedure [3]. Newer techniques such as high-intensity focused ultrasound have been employed in the treatment of osteoid osteoma which has shown a clinical success rate of up to 90% [4]. MRI is used to plan and monitor temperature changes during the procedure and a high frequency external ultrasound transducer is used to causes local heating and coagulative necrosis.

Take Home Message: CT-guided radiofrequency ablation is a highly effective and reliable treatment of osteiod osteoma.

Written informed patient consent for publication has been obtained.