IgG4-related lesion of the retroperitoneum, ureter, and kidney, mimicking infiltrating endometriosis

Urinary tract endometriosis is rare, and ureteral involvement is particularly insidious due to its asymptomatic nature. The absence of symptoms can lead to ureteral stricture, hydronephrosis, chronic kidney disease up to end-stage renal failure, and irreversible loss of kidney function. Diagnosis requires imaging methods to assess the degree of obstruction, while treatment involves surgical release of the ureter from endometriotic infiltrates to preserve organ function. Our observation illustrates the difficulty of establishing the etiology of a retroperitoneal tumor-like infiltrate leading to ureteral obstruction and hydronephrosis, as well as the need for differential diagnosis of endometriosis with other infiltrative processes.