Osteoid osteoma is a very common benign tumor of bone and accounts for 2% to 3% of all bone tumors and 10% to 20% of benign bone tumors.1It is two to three times more frequent in males and is most common between 5 and 20 years of age. Osteoid osteoma most commonly involves the long bones of the legs but may occur in any bone including the hands and the spine where it is the most common cause of painful scoliosis in skeletally immature individuals.2
Pain is the most common presentation of osteoid osteoma. It is mediated by the proliferation of nerve endings in the tumor and a high level of prostaglandins in the nidus, which accounts for the exquisite responsiveness of the pain to NSAIDs.3 The pain is usually mild and intermittent but then becomes continuous and severe and tends to be worse at night. Patients may have point tenderness, a swollen limb, and/or a tender palpable mass; or they may present with a painless limp. Osteoid osteomas in the joints may mimic arthropathy whereas those in the spine may present with scoliosis, torticollis, hyperlordosis, or kyphoscoliosis. Osteoid osteomas that are close to the growth plates may lead to growth disturbance and limb-length discrepancies or angular deviations. If the diagnosis of osteoid osteoma is delayed, patients may present with chronic pain or limping as well as atrophy of the affected limb.
Clinical history and radiographs are usually sufficient to diagnose osteoid osteoma (histologic confirmation is not necessary). The typical radiographic appearance of a cortical osteoid osteoma is of a small (<1 cm)radiolucent round or oval area of osteolysis (nidus), surrounded by a regular ring of bony sclerosis (Fig. 111-1). The entire entity rarely exceeds 1.5 cm. In some cases, the center of the nidus may have an irregular nucleus of bone density giving a cockade appearance. The bone circumference may be increased. Cortical diaphyseal lesions may produce an oblong thickening to one side of the shaft. In these lesions, the nidus lies at the center of the thickening and may be contained within the primary cortex or oriented toward the endosteal or periosteal side of the bone. The surrounding reactive bone may be sufficiently dense as to obscure the nidus. With a medullary osteoid osteoma, osteosclerosis may be minimal or absent because of the lack of adjacent periosteum as the absence of periosteum limits the bone's ability to mount a proliferative response. If osteosclerosis is present with a medullary osteoid osteoma, it may be located away from the lesion. Joint space widening may occur in the presence of synovitis. Osteoid osteomas of the spine typically involve the posterior elements and may be difficult to visualize on plain radiographs; films may be normal or demonstrate only osteosclerosis.
Osteoid osteoma of the proximal tibia.
If conventional radiography is insufficient, computed tomography (CT) and isotope bone scans may aid in the diagnosis of osteoid osteoma. CT using bone windows will show the nidus of the osteoid osteoma as a well-defined, rounded area of decreased attenuation with a smooth periphery surrounded by a variable amount of reactive sclerosis. The hypervascular nidus of an osteoid osteoma may also be demonstrated on a contrast-enhanced CT scan. Because of the small size of the tumor, however, the CT scan should be performed in thin sections (1–2 mm). On bone scans, the double density sign is described from the small, rounded area of intense uptake (the nidus) centered in a less intensely positive and more diffuse halo (peripheral hypervascularization and sclerosis). Magnetic resonance imaging (MRI) shows intense bone marrow edema adjacent to the nidus although the nidus itself may not be visible.2
Osteoid osteomas tend to be nonprogressive and may resolve over the course of years. Medical management with prolonged use of NSAIDs is an option but, severe pain, intolerance of NSAIDs, and disuse muscle atrophy mandates removal of the nidus as a curative intervention. Techniques include radiofrequency ablation (considered by many to be the treatment of choice4); wide surgical excision; intralesional excision; arthroscopic, CT and MRI-guided core drill excision; injection of ethanol; interstitial laser photocoagulation; and a variety of minimally invasive surgeries. If the nidus is not removed completely, the patient may have persistent pain.