Diagnosis for Parapelvic Kidney Cysts

Parapelvic cysts of the kidneys are one common type of simple cysts, which are adjacent to the renal pelvis or the renal sinus.
B ultrasound should be sufficient for the diagnosis; in doubtful situations an intravenous pyelography, CT scan or renal scintigraphy can rule out urinary obstruction. And in case of parapelvic kidney cysts, it should be distinguished with hydronephrosis (upper urinary tract obstruction).
A parapelvic renal cyst is usually identified during excretory urography as a mass causing extrinsic compression on the renal pelvis. This appearance is nonspecific, however, and the etilology of such a mass must be further investigated. Recently computed tomography (CT) and sonography have replaced angiography as the preferred methods of evaluating masses in this region. The CT appearance of tumors involving the renal pelvis has recently been reported, but the spectrum of findings with parapelvic cysts has not been described. Their recognition is important in order to avoid invasive diagnostic evaluation. The appearance of parapelvic cysts on both CT and sonography may mimic hydronephrosis and unnecessarily lead to further studies. Parapelvic kidney cysts need to be distinguished with renal hilar masses and hydronephrosis.
We found that on CT, a parapelvic cyst has smooth or lobulated margins. The lobulated appearance often suggested that either multiple small adjacent cysts were present or a single large cyst had multiple lobulations. Differentiation of these two possibilities is not possible unless surgery or cyst puncture with injection of contrast material is performed. Although surgical proof was not obtained in most of our cases, the CT criteria we used were identical to those shown to be virtually pathognomonic for cysts of the renal parenchyma.
On sonography, a parapelvic cyst appears as an anechoic mass with a well demarcated wall. The part of the wall projecting into the renal sinus is thick and echogenic because it is surrounded by the prominent pelvocalyceal echo complex which is composed of fibrous tissues, sinus fat, vessels, and collecting systems. The echos arising from the cyst wall cannot be distinguished from those arising from the adjacent renal sinus tissue. This thickened appearance of the cyst wall is also noted on CT. The part of the wall projecting into the renal parenchyma or perinephric tissue has the same wall characteristics of simple parenchymal cysts.