Name : Hamid
Affiliation : Radiology Department,Loghman Hakim Hospital,SBMU
Academic Degree: Assistant Professor of Radiology
Resident : Hussein Soleiman Tabar
Gender : Male
Age : 18
A 18-year-old male presenting with hip pain, exacerbating at nights
Imaging Procedures and Findings
Plain radiographs show a sclerotic area in the right acetabulum. CT images depict the sclerotic acetabular lesion abutting the articular surface. The lesion has a central lucent nidus which is centrally calcified. On MRI the lesion is low signal with no surrounding bone edema.
Osteoid osteomas are relatively common; only osteochondromas and fibrous cortical defects are more prevalent. The male-to-female ratio is 3:1. They typically occur in teenagers and young adults and are rare before 5 years and after 30 years of age. These tumors occur most frequently in the femur, tibia, and humerus and involve the diaphysis and, less commonly, the metaphysis. When the spine is involved, the posterior elements are typically affected. The main clinical symptom is pain relieved by aspirin. CT is very accurate in detecting the nidus and is preferable to MRI for evaluating osteoid osteoma. Occasionally, an osteoid osteoma can be confused with a stress fracture on MRI because of edema in the bone marrow. On CT the typical appearance of an osteoid osteoma is an area of sclerosis surrounding a small Â«1 cm) radiolucent nidus. Lesions larger than 1.5 cm are considered osteoblastomas. The nidus may contain a variable number of calcifications, ranging from none to enough to cause almost complete calcification, with only a thin peripheral rim of low density. For full evaluation of the nidus, thin-section CT with less than 2-mm slices is needed because the nidus is often less than 1 cm in diameter. The nidus enhances on dynamic CT scans; this enhancement help in differentiating osteoid osteoma from Brodie's abscess. Depending on the degree of calcification, the nidus has low signal intensity on Tl-weighted images and variable intensity on T2-weighted images. The surrounding bone marrow has low signal intensity on all pulse sequences in the presence of reactive sclerosis or high signal intensity on T2-weighted images in the presence of edema. Osteoid osteomas in younger patients tend to be associated with more extensive peritumoral edema. When the osteoid osteoma is intraarticular, an associated joint effusion may be detected. CT is used to direct percutaneous ablation of osteoid osteomas.
CT and MR imaging of the whole body / [edited by] John R. Haaga ... jet al.].-5th ed