Figure 7. Retroperitoneal abscess in an obese woman with a history of resected colon cancer 2.5 years earlier who presented to the emergency department at 30 weeks gestation with right flank pain. US was performed at another institution; the results were interpreted as showing a solid right renal mass. Coronal single-shot turbo spin-echo image shows that the abnormality actually consists of fluid (arrow), which displaces the kidney (arrowhead). The diagnosis of an abscess was confirmed at drainage, although the cause was not definitively ascertained.