Postpartum Retroperitoneal Fibrosis With IVC Obstruction: A Case Report.

Retroperitoneal fibrosis (RPF) is a rare fibroinflammatory condition producing inflammatory masses in the retroperitoneum that can obstruct retroperitoneal structures, including vessels and ureters. RPF typically presents in middle-aged men and may be associated with IgG-4-related disease (IgG-4 RD). This report describes a 34-year-old woman who presented 6 months postpartum with left leg swelling and lower abdominal pain. Contrast-enhanced CT revealed a homogenous retroperitoneal soft-tissue mass encasing the aorta and iliac arteries, with inferior vena cava (IVC) obstruction and collateral venous return through extensive pelvic varices. MRI findings included hypointensity on T2-weighted imaging and restricted diffusion. Management with thrombolytics and steroids resulted in recanalization of the IVC, though persistent hydronephrosis required nephrostomy and further urological intervention. The presentation of RPF in a young woman is unusual, and we theorize that immune system reactivation following the relative immunosuppression during pregnancy may have precipitated the condition. The case illustrates one of several immunologic factors associated with RPF.