As urine extravasates into the retroperitoneum, it can cause lipolysis of the surrounding fat with resultant encapsulation of urine, forming a urinoma.
Urinomas most often due to urinary obstruction secondary to 2-3:
- ureteropelvic junction obstruction
- retroperitoneal fibrosis
- retroperitoneal malignancy
- cancer of the renal pelvis, ureter, or bladder
- a variety of conditions that cause bladder outlet obstruction
Urinomas also may be due to:
- abdominopelvic trauma, e.g. renal trauma or bladder rupture
- surgery, e.g. ureteric injury
- diagnostic instrumentation, e.g. ESWL or ureteroscopy
Location and morphology
- cystic mass in perirenal space: localized perirenal urinoma (most common)
- cystic mass filling entire perirenal space: diffuse perirenal urinoma
- sickle-shaped collection: subcapsular urinoma
- encapsulated expanding intrarenal cystic mass separating renal tissue fragments: intrarenal urinoma 3
CT and MRI
On CT and MRI, a urinoma shows water attenuation, low signal intensity on T1-weighted imaging, and very high signal intensity on T2-weighted imaging, similar to simple fluid elsewhere in the body.
Urine leakage is usually directly demonstrated on contrast-enhanced CT or T1-weighted imaging, seen as enhancement of the fluid during the excretory phase of enhancement due to contrast extravasation from the lumen of the genitourinary system 2.
Contrast extravasates outside of the collecting system, into the surrounding retroperitoneal tissues.
Treatment and prognosis
- small urinomas: usually treated conservatively
- larger, persistent or symptomatic urinomas: percutaneous drainage is often used with treatment of the underlying cause of urine leakage
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