RADIATION-INDUCED INSUFFICIENCY FRACTURES OF THE SACRUM - EVALUATION WITH MR-IMAGING

In patients with malignant pelvic tumors, radiation-induced insufficie ncy fractures of the sacrum may be mistaken for metastasis. Magnetic r esonance (MR) imaging was performed in 18 patients with this condition , and the findings were studied retrospectively. The diagnosis was con firmed with at least one additional imaging modality in 16 patients, w hereas the other two patients underwent clinical follow-up at 13 and 2 0 months without evidence of metastasis. In 17 patients, the lesions w ere consistent with edema and had diffuse low signal intensity on T1-w eighted images and diffuse high signal intensity on short-inversion-ti me inversion-recovery images, thereby simulating metastasis. In one pa tient, bilateral sacral wing fractures were demonstrated directly as f airly well-defined linear zones. The alae sacri were involved in all p atients; 16 patients had bilateral lesions. Awareness of this clinical entity and of the high sensitivity of MR imaging for demonstrating ed ema caused by the fracture should prevent confusion with metastatic di sease and inappropriate treatment.