Clinical Presentation

The patient is a 40-year-old woman with polysubstance abuse and severe low back pain.

(A–C) Axial computed tomographic scan through the sacroiliac (SI) joints shows extensive erosion of the left SI joint (A, white arrow) with an anterior rim-enhancing fluid collection (B, black arrow). Radionuclide examination shows increased uptake over the left SI joint (C, arrow).