Imaging Review of Skeletal Tumors of the Pelvis—Part I: Benign Tumors of the Pelvis

Figure 3

50-year-old male with osteoblastoma (aka giant osteoid osteoma) involving the left iliac bone. Plain radiograph (a) shows a large lytic left iliac bone lesion (asterisk) with sharp sclerotic borders. An angiographic image (b) with a 5 French cobra catheter (curved arrow) in the left common iliac artery demonstrates the vascular nature of the tumor, with the tumor blush (asterisk) predominantly supplied by the superior gluteal artery which was subsequently embolised a day prior to surgical resection. The axial CT (c) and axial T2 MRI (d) demonstrates the mass originating from the outer cortex of the right iliac bone. It has a narrow zone of transition with distinct borders. Edema is noted in the iliac bone (B) and the gluteal musculature (M) on the fluid sensitive T2 MRI sequence demonstrating the aggressive nature of this benign lesion. Axial T2 MRI (e) 5 years postresection demonstrates unusual progression to high grade osteoblastic osteosarcoma (arrows). Even though benign, osteoblastomas can be locally aggressive, recur or differentiate to a malignant aggressive tumor, in this case necessitating a revision hemipelvectomy.