Sequestra in prostate cancer metastases: CT and MR appearance

Objective: To determine the frequency and distribution of sequestra in osseous metastases from prostate cancer and define their CT and MR imaging features. Materials and Methods: We retrospectively reviewed CT and MR imaging in 96 patients with prostate cancer osseous metastases for a 3-year period (1997-2000). Pathologic diagnosis of prostate metastases was made by core biopsy in 20 of these patients. Diagnosis of osseous metastatic disease was established by bone scans in the remaining 76 patients. The presence or absence and size of sequestra were recorded in these two groups of patients. The CT attenuation, MR signal characteristics of sequestra and surrounding marrow were noted in the two groups. Results: Sequestra were noted in 20 of 96 patients (21%) with prostate cancer metastases or in 18% of all prostate cancer osseous metastases. Sixteen percent of lesions in the biopsy-proven group and 18% of lesions in a non-biopsy bone scan diagnosis group displayed characteristics of sequestra. The locations of 96 sequestra were as follows: thoracic spine (n = 17), lumbar spine (n = 24), proximal femur (n = 11), sacrum (n = 18), ilium (n = 22), and humerus (n = 4). The CT appearance of sequestra was that of a high-attenuation osseous lesion surrounded by a low-attenuation rim separating it from the rest of the bone marrow. Sequestra were of low signal intensity on T1-weighted and T2-weighted fast-spin echo sequence, separated from the rest of the surrounding marrow by a thin rim of low- to intermediate-signal intensity on T1-weighted and hyperintense signal intensity on T2-weighted sequences. The gadolinium-enhanced fat-saturated T1-weighted MR imaging showed enhancement of the sequestrum. Conclusion: Sequestra can be seen with metastatic disease from prostate cancer, which should be included in the differential diagnosis of this entity in addition to other conditions, including osteomyelitis, eosinophilic granuloma, fibrosarcoma, desmoplastic fibroma, malignant fibrous histiocytoma, and primary lymphoma of bone.