Left iliac bone para-sacroiliac joint expansion with marrow infiltration, surrounding cortical disruption, aggressive periosteal reaction (spiculated) and sizable circumferential soft tissue mass showing intra and extrapelvic components. The extrapelvic soft tissue component is more sizable posteriorly and laterally infiltrating the left gluteus medius muscle and stretching the gluteus maximus muscle. The intrapelvic soft tissue component is seen infiltrating the iliacus and psoas muscles. The mass is eliciting homogenous intermediate signal on T1 WIs and low to intermediate signal on T2 WIs with heterogenous vivid post contrast enhancement.
Obliterated left sacroiliac joint by the neoplastic process with adjacent sacral marrow infiltration.