[Treatment of osteoid osteoma by CT-controlled percutaneous drill resection. Apropos of 27 cases].

Purpose Of The Study: Osteoid osteoma is a benign tumor requiring excision due to pain, usually severe and invalidating. Surgical "en bloc" resection is not always easy. Complete resection of the nidus is required to prevent recurrence while at the same time a limited resection should also be used to avoid a pathological fracture or a growth plate injury in children. In order to achieve these 2 goals, we have developed an alternative method: CT guided drill resection. This method is reported with special reference to its technical aspects.

Material And Methods: Twenty seven patients (16 children and 11 young adults) were treated during a seven year period (June 87 through June 94) and observed clinically and radiologically with an average two-year follow-up (range one to three years). Osteoid osteoma was localized mainly in the lower limb: Femoral neck (or head): 10 cases, 3 in the acetabulum; Femoral shaft: 6 cases; Tibial shaft: 4 cases. Diagnosis was based on clinical features and imaging: radioisotope bone scan and computed tomography in all cases--angiography in 3 patients to assess the diagnosis more accurately. The procedure was performed under general anesthesia (a short hospitalization is needed). The nidus was first localized by Computed Tomography, then approached and resected through a small percutaneous incision. A special device has been manufactured in order to remove a bone cylinder containing the nidus. It was thus possible to perform histological studies of the specimen and confirm the diagnosis. Histological confirmation was possible in 50 per cent of the cases. No complication (except a case of transient extensor hallucis palsy) was observed in this series, 24 patients healed completely; pain disappeared immediately, and the control CT scan returned to normal after a one-year follow-up. In 3 patients, because of a technical error, the nidus was not totally removed. These patients underwent a second procedure, which was effective.

Discussion: This method is a good alternative to the direct surgical approach because of its technical advantages: precision in nidus localization and minimal bone resection; consequently, one should underline the practical benefits for the patient: short hospitalization, immediate full weight bearing, quick return to socio-economic activities. Furthermore, some localizations of the nidus which are difficult to reach (for instance the acetabulum) represent a good indication for the method. Accurate pre-operative diagnosis has now become possible with recent advances in imaging techniques but still remains "uncertain". The resection of the specimen allows confirmation of the diagnosis is most of cases. This procedure should ideally be performed by a team (orthopedic surgeon and a radiologist): collaboration instead of competition is in fact the best way to progress in this field of "interventionnal radiology".