Rare perinephric myxoid pseudotumor of fat causing ureteropelvic junction obstruction: a case report.

Ureteropelvic junction obstruction (UPJO) is a congenital or acquired functionally significant impairment of urinary transport from the renal pelvis to the ureter. Congenital UPJO typically results from intrinsic disease such as the presence of an aperistaltic segment of the ureter, aberrant vessels or kidney abnormalities. Rare conditions can sometimes mimic an UPJO. We present a case of an 86-year-old woman with a UPJO diagnosed on CT. The patient was counseled on treatment options and elected to undergo a left uretherorenoscopy (URS) plus left laparoscopic pyeloplasty. The definitive histopathologic diagnosis was perinephric myxoid pseudotumor of fat, an extremely rare neoplasm, mass-forming. To the best of our knowledge, this is the first known case of a pseudotumor of fat causing UPJO. 6-month follow-up showed neither recurrence nor residual UPJO. We describe a rare presentation of extrinsic perinephric myxoid pseudotumor of fat causing UPJ obstruction. In elderly patients with no history of malignancy, UPJ obstruction can occur because of atypical masses.