urinomas

Urinomas are localized collections of urine outside the urinary tract, most commonly in the retroperitoneal or perirenal space, caused by leakage from the renal collecting system, ureter, or bladder. They are typically sterile initially but may become infected if leakage persists.

Causes include blunt or penetrating renal trauma; iatrogenic injuries during surgery or endourologic procedures (for example after pyeloplasty, ureteral repair, lithotripsy, catheter placement); obstruction from stones or stricture; and complications after kidney transplantation.

Pathophysiology: Urine escapes from the collecting system into a confined space, forming a fluid collection bounded by inflammatory tissue. The collection can enlarge, compress adjacent structures, and predispose to infection. Drainage or diversion of urine often allows the leak to heal while the collection gradually resolves.

Clinical features: Presents with flank or abdominal pain, a palpable mass, fever or malaise if infected, and sometimes signs of urinary leakage such as persistent drain fluid with elevated creatinine or urine odor. Onset is often days to weeks after trauma or surgery.

Diagnosis: Ultrasound is commonly used for initial assessment; CT urography or contrast-enhanced CT delineates the collection and the site of leakage. Analysis of drained fluid showing creatinine content similar to urine supports urinoma; nuclear medicine studies or retrograde pyelography may identify the leak source.

Management and prognosis: Small, asymptomatic urinomas may be observed with close follow-up. Larger or symptomatic urinomas, or those suspected of infection, usually require percutaneous catheter drainage and urinary diversion (stent or nephrostomy) to reduce urine leakage. Definitive repair targets the source of leakage; antibiotic therapy is used for infected collections. Prognosis is generally favorable with timely management, though complications include infection, abscess formation, persistent leak, and impaired renal function.