1、Radiologic Diagnosis of Osteoid Osteoma,Osteoid osteoma is a benign bone tumor that occurs most frequently in men and boys between 7 and 25 years old . Most patients experience pain that worsens at night and is promptly relieved by the administration of salicylates 。,Typical radiographic findings of
2、 osteoid osteoma include an intracortical nidus, which may display a variable amount of mineralization, accompanied by cortical thickening and reactive sclerosis in a long bone shaft.,At CT, the nidus is well defined and round or oval with low attenuation (Fig 2). An area of high attenuation may be
3、seen centrally, a finding that represents mineralized osteoid (Fig 3).,MR imaging depicts not only the nidus and accompanying sclerosis but also adjacent bone marrow and articular abnormalities 。 The nidus has low to intermediate signal intensity on T1-weighted images and variable signal intensity o
4、n T2-weighted images, depending on the amount of mineralization present in the center of the nidus.,Edema in adjacent bone marrow and soft tissue and joint effusion also may be seen (Fig 3) 。 Several studies have shown that, compared with CT, MR imaging is of limited value in depicting the nidus 。 M
5、R imaging sometimes fails to depict small nidi, because the signal in the nidus often is similar to that in cortical bone (Fig 4).,Intraarticular Osteoid Osteoma,Intraarticular osteoid osteoma, which occurs within or near a joint, is considered a separate clinical entity 。 The most commonly involved
6、 joint is the hip. The ankle, elbow, wrist, and knee are less commonly affected 。,Imaging findings of intraarticular osteoid osteoma differ from those of intracortical osteoid osteoma. With intraarticular osteoid osteoma, reactive cortical thickening is minimal or absent, a finding believed to be du
7、e to a lack of cambium, the inner layer of the periosteum.,Uncommon Locations of Osteoid Osteoma,Osteoid osteoma is most common in the femur and tibia; more than 50% of cases occur in these locations. Approximately 30% of osteoid osteomas occur in the spine, hands, or feet 。 The least common locatio
8、ns are the skull, scapula, ribs, pelvis, mandible, and patella (Fig 7) 。,The most common location of spinal osteoid osteoma is the lumbar segment (Fig 8), followed by the cervical segment and the thoracic segment. The sacrum is the least commonly affected spinal segment (Fig 9) 。,In the hands and fe
9、et, cancellous osteoid osteoma occurs in the carpal and tarsal bones, and all types of osteoid osteoma may occur in the metacarpal, metatarsal, and phalangeal bones (Fig 10).,Confusing Imaging Findings,When osteoid osteoma is accompanied by severe inflammatory changes such as a prominent periosteal
10、reaction, exaggerated synovial hypertrophy and joint effusion, and extensive bone marrow and soft-tissue edema, it may be difficult to reach a diagnosis 。,Stress Fracture,A stress fracture appears as an infraction in the center of an area of cortical thickening, whereas osteoid osteoma appears as a
11、round nidus (Fig 13) In a stress fracture, the extent of cortical thickening varies from a focal cortical ridge to extensive thickening that is bidirectional to the periosteal and endosteal aspects. In osteoid osteoma, the extent of cortical thickening depends on the transverse and longitudinal loca
12、tion of the tumor in bone, but no prominent cortical ridges are present.,Intracortical Abscess,it is easier to differentiate between the two conditions at CT. In osteoid osteoma, the inner side of the nidus is smooth, and a round calcification is seen in the center of the nidus. In an intracortical
13、abscess, the inner margin is irregular, and an irregularly shaped sequestrum is seen eccentrically (Fig 14),Other Tumors and Tumorlike Lesions,Intracortical Hemangioma A typical radiographic finding of intracortical hemangioma is an intracortical osteolytic lesion with cortical thickening or periost
14、itis (Fig 15).,Chondroblastoma. A chondroblastoma is an uncommon benign chondroid tumor that is usually less than 4 cm long. Similar to osteoid osteoma, it frequently occurs in the young and is aggressive, with periosteal reaction and extensive bone marrow edema seen at imaging 。,An epiphyseal and i
15、ntramedullary location may help differentiate a chondroblastoma from an osteoid osteoma, which is commonly diaphyseal and intracortical (Fig 16),Osteoblastoma At imaging, osteoblastoma usually appears more expansile, is larger than 2 cm, and has less reactive sclerosis surrounding the mass than osteoid osteoma does (Fig 17),谢谢！,
