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.¹ It 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 metaphyseal and diaphyseal areas of 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 to NSAIDs.³ When the osteoid osteoma is intra- or juxta-articular it can also induce a synovitis pain that is less responsive to NSAIDs.⁴

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 cause growth disturbance and limb-length discrepancies or angular deviations. Patients may present with chronic pain or limping as well as atrophy of the affected limb if the diagnosis of osteoid osteoma is delayed.

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 or partially calcified round or oval area of osteolysis (nidus), surrounded by a sclerotic margin (Fig. 112-1). The entire entity rarely exceeds 2 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.

If conventional radiography is insufficient, obtain computed tomography (CT) and/or isotope bone scans to 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 NSAIDs is an option. Removal of the nidus is recommended for severe pain, intolerance of NSAIDs, and disuse muscle atrophy: surgical resection or radiofrequency ablation are removal options. The patient may have persistent pain if the nidus is not removed completely.

NOFs, also known as fibrous cortical defects, metaphyseal fibrous defects, and cortical desmoids, are extremely common fibrous lesions seen in up to 40% of preadolescents and adolescents.⁵ They are rarely found in adults, and when followed radiographically over time, usually fill in with normal bone during adolescence.⁶ They tend to be asymptomatic and are usually discovered incidentally but occasionally present with pain from a pathologic fracture. Infrequently, the fibroma may cause chronic pain. NOFs may occur in multiple bones.

Radiographs reveal an eccentric lucency in the metaphyseal cortex that has sharp margins and surrounding sclerosis. Lesions may be multilocular and expansive with extension into the medullary bone. The long axis of the fibroma parallels the long axis of the bone. With an overlying stress fracture and associated periosteal reaction, NOFs may be mistaken for osteogenic sarcomas. NOFs may also have an atypical appearance if they are discovered as they are filling in with normal bone. CT scanning may be helpful if plain radiographs are not diagnostic. NOFs with a characteristic radiographic appearance do not require biopsy.

Routine follow-up for asymptomatic NOFs is controversial. Fibromas found in young children may increase in size relative to the growth of the adjacent bone and place the bone at risk for fracture. Therefore, consider yearly or semi-annual radiographs in younger patients until the lesion is stable in size relative to the involved bone. NOFs discovered in adolescence do not require follow-up.

The majority of NOFs do not require treatment. Lesions greater than 50% of the width of the bone or smaller lesions in areas of high stress may be considered for curettage and bone grafting because of the risk of associated pathologic fracture.⁶ Injection, extensive burring, chemical, thermal, or other adjuvants are not required. Recurrence is rare.