Parapelvic cyst misdiagnosed as hydronephrosis

A 37-year-old male was referred to our hospital due to an abnormal ultrasound report of the right kidney in a regular health examination. The patient was asymptomatic and did not report fever, flank pain or dysuria. Repeated ultrasonography at our hospital revealed a hypoechoic area in the right central renal sinus, suggesting right hydronephrosis, but the obstructive site could not be found (Figure 1). Urinalysis revealed clear urine, and urine cytology was negative for malignant cells. For further evaluation of the obstructive site for the hydronephrosis, a computed tomography (CT) scan was arranged (Figure 2). It revealed a parapelvic cyst with mild displacement of the collecting system but no hydronephrosis was noted. As there were no symptoms, the patient was followed up without further treatment. Parapelvic cysts are uncommon and found in ∼1.25– 1.5% of autopsy cases [1]. Parapelvic cysts are usually solitary, originating from renal parenchyma and protruding into the sinus. Because of the hypoechoic character by ultrasonography and the special location in the renal sinus, parapelvic cysts are often misdiagnosed as hydronephrosis [2]. A large parapelvic cyst may sometimes compress the collecting system causing hydronephrosis, which needs surgical intervention [3]. Parapelvic cysts are rare and often benign and must be differentiated from hydronephrosis. The possibility of a parapelvic cyst must be kept in mind when the asymptomatic hydronephrosis is noted by ultrasonography with unknown causative obstructive lesion. Further image study such as CT scan is needed for the correct diagnosis. Fig. 1. Renal ultrasonography revealed a hypoechoic area at central sinus region, suggesting hydronephrosis.