Imaging findings on admission. (a) A coronal T2-weighted magnetic resonance image (repetition time [TR] of 3800 and echo time [TE] of 74,932) shows a mass of low signal intensity within the pelvis (area surrounded by arrows). (b) A short T1 inversion recovery (STIR) image of magnetic resonance imaging (TR of 3700 and TE of 58,786) shows a small area of high density within the low-density lesion (surrounded by arrows). (c) High-resolution coronal computed tomography images show penetration of innominate acetabular bone (with partial bone resorption) by the screw tip and a large low-density lesion. (d) Three-dimensional magnetic resonance angiography shows a large abnormal lesion that is located between the external and internal artery and vein and that extends widely to the obturator foramen or foramen obturatum.