Perinephric urinoma

Perinephric urinoma


A perinephric (or paranephric) urinoma is a fluid-filled cyst which forms usually secondary to rupture of a dilated renal pelvis. Urinomas may rupture to cause urinary ascites or resolve spontaneously. They may enlarge and compress adjacent structures including the thorax which can lead to lung growth impairment. The aetiology of the urinoma varies dependent upon the nature and severity of the obstructive lesion (e.g. ureteropelvic junction obstruction). The prognosis for the kidney(s) adjacent to the urinoma is poor.


A fluid-filled mass (often quite large) can be demonstrated adjacent to the kidney. Usually the kidney is hydronephrotic and can be displaced by the mass. The abdominal aorta may also be displaced by the mass as well as other abdominal structures. The diaphragm may be elevated and lung tissue compressed. If unilateral, abnormalities of the contralateral kidney should be sought especially if there is low or absent amniotic fluid. Other organ system malformations may be present especially if polyhydramnios is present. Perinephric urinoma can be found as a result of obstructive sequences including PUV, UVJ, and UPJ and may be as a result of syndromes described under these headings.

Differential Diagnosis

A perinephric urinoma is usually more elliptical in shape than a large simple renal cyst. Also, parenchyma may be demonstrated surrounding a simple renal cyst. Ovarian cysts, mesenteric cysts and dilated loops of bowel are less likely to cause elevation of the diaphragm and should not displace retroperitoneal structures such as the aorta. Other retroperitoneal cysts or tumours with necrosis and cystic degeneration may be distinguished by location relative to the kidneys or by presence of solid components.

Sonographic Features

Cystic mass adjacent to kidney

Associated with severe hydronephrosis

Bilateral or unilateral

If unilateral, abnormalities (including absence of contralateral kidney frequent)

Oligohydramnios frequent if obstruction or renal abnormalities are bilateral

Normal or increased fluid volume can occur with bilateral obstruction if other malformations are present (gastrointestinal blockage, diaphragmatic hernia etc)

May cause elevation of diaphragm and compressed lung(s)

Associated Syndromes 


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