Name : Akbar
Affiliation : Temple University School of Medicine
Academic Degree: Emeritus Professor of Radiology and Former professor of Orthopedic Surgery
Two patients with different diagnosis but a common radiographic sign!
Imaging Procedures and Findings
Both plain radiographs show elliptical periosteal reaction in diaphysis of the femur. The lesion in the first patient (image-1) contains a horizontal radiolucent band and peripheral sclerosis and has resolved during a follow-up period which is compatible with stress fracture. A radiolucent lesion within the area of fusiform cortical thickening is evident on image-2 and the diagnosis was osteoid osteoma.
Typical radiographic findings of 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. The radiolucent focus often is referred to as the nidus because the focus usually is located in the center of an area of reactive sclerosis. The nidus is round or oval and usually smaller than 2 cm. Several conditions have imaging findings that may mimic osteoid osteoma, such as localized cortical thickening, reactive sclerosis surrounding an osteolytic lesion, and bone marrow edema. These conditions include stress fracture, intracortical abscess, intracortical hemangioma, chondroblastoma, osteoblastoma, and compensatory hypertrophy of the pedicle.
Stress fracture is common in the diaphysis of lower-extremity bones and the femoral. 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 location of the tumor in bone, but no prominent cortical ridges are present. A stress fracture is more likely than osteoid osteoma if the size of the cortical lesion decreases during a short follow-up period, although there are a few reports of spontaneous regression of an osteoid osteoma. Bone scintigraphy may help differentiate a stress fracture from osteoid osteoma. On scintigraphic images, a stress fracture demonstrates linear, intense uptake of the tracer, whereas osteoid osteoma displays the ??double-densityÃ¢?Â sign, in which intense central uptake is seen at the site of the nidus and moderate uptake is seen in the surrounding area.
Stress Fracture versus Osteiod Osteoma in distal femur
1-Chai JW et al. Radiologic Diagnosis of Osteoid Osteoma: From Simple to Challenging Findings. RadioGraphics. 2010; 30: 737-749.
2-Bonakdarpour, A., Reinus, W. R., Khurana, J. S. Diagnostic Imaging of Musculoskeletal Diseases, A Systematic Approach. Springer, 2010, 262-264 and 276.