Ans. c (Osteoid osteoma). (Ref. Maheshwari, Orthopaedics, 3rd ed., 214; Refer to above Q.)OSTEIOD OSTEOMA# The most common benign osteoid-forming tumor is the osteoid osteoma, accounting for 10% of all benign bone umors.# It is more common in males than in females, with a peak incidence in the second decade of life.# The proximal femur is the most common site.# Dull aching pain is the most frequent symptom.# Symptoms are relieved with (NSAIDs) secondary to a high concentration of prostaglandins in the nidus.# Osteoid osteoma may have a unique pathogenic nerve supply as well, a unique finding among bone tumors.# The characteristic radiographic feature of the osteoid osteoma is the central lytic nidus that measures up to 1 cm in diameter. In the common cortical lesion, an extensive reactive sclerosis is evident, creating a fusiform bulge on the bone surface.# Technetium-MDP bone scans are invariably positive (Double density sign).# A CT scan is helpful to better anatomically locate the lesion in preoperative planning.# Nidus in osteoid osteoma is diagnostic (well seen on CT).# In the spine, the typical location for an osteoid osteoma is in the posterior elements, such as the lamina or pedicle. The lumbar spine is most commonly involved.# Rx:- Intralesional resection via the so-called burr-down technique is generally preferred over en bloc resection.- CT-guided radiofrequencv ablation (RFA) is reported as an effective, less invasive method of treating osteoid osteoma.* This method employs probes with high-frequency alternating current to induce ionic agitation and frictional heat to cause tumor necrosis.RFA is used extensively as a less invasive treatment modality with similar success rate as surgical excision.