Fig. 1

Computed tomography of the thorax, abdomen, and pelvis with contrast performed when the patient presented with foot drop. Serial axial computed tomography images: (i) and (ii) demonstrate an infiltrative heterogeneous soft tissue mass-like abnormality involving the left pelvic sidewall and presacral space (red arrows) intimately involving the left obturator internus and piriformis muscle (yellow arrow). Dystrophic areas of calcification are seen within the soft tissue mass. Despite the ill-defined and infiltrative nature, there is no associated bony destruction. Image (iii) depicts left iliac chain lymphadenopathy (purple arrow); image (iv) shows a loss of the normal subcutaneous fat, soft tissue thickening and multiple, punctate calcifications overlying the left gluteal maximus muscle, suggesting a chronic process (green arrow)