Although uncommon, hydatid cysts do occur in the kidneys, with Echinococcus granulosus being more common than Echinococcus multilocularis. In rare instances renal cysts develop bilaterally. Ureteral cysts are rare. No age group is immune, including children. Patients are often asymptomatic until the pressure on an adjacent structure or cyst rupture develops. Rupture into a collecting system leads to hydatiduria and possible renal colic due to cyst debris.
Extensive cyst wall calcifications are common. A typical appearance is a calcified tumor compressing the pelvicalyceal system or ureter, at times identified even with conventional radiography. Similar to the liver, some cysts contain mural nodules. The presence of a solid component within a cyst mimics a renal cell carcinoma. At times “sand” is detected in the dependent portion of a cyst. Daughter cysts lead to a multiloculated appearance. In time, calcified daughter cysts result in a cysts-within-a-cyst appearance, a finding suggesting the diagnosis. Most hydatid cysts have mixed echogenicity on US. As in the liver, percutaneous drainage of renal hydatid cysts is a therapeutic option.
Radiology images of primary renal hydatid disease. Unenhanced CT reveals a hypodense tumor in the left kidney. Peripheral daughter cysts and calcifications are evident.