Teaching Case

A 77-year-old female patient presented in the emergency department with right lumbar pain, dysuria and fever. In this setting a renal ultrasound and subsequently an abdominal CT were performed.

The renal ultrasound revealed dilatation of the collecting system in the right kidney and reduced thickness of the parenchyma, consistent with chronic obstructive uropathy (Fig. 1). It also showed the presence of at least one renal sinus cyst.
In order to detect the obstructive cause a CT was obtained.
The CT confirmed the US findings - dilated calyces and reduced thickness of the renal parenchyma. Interestingly, it also showed that the obstructive cause was a large renal sinus cyst (Fig. 2), a finding better appreciated in the excretory phase. The pelviureteric junction was compressed and deviated posteriorly by the cyst. Additionally, the pelviureteric junction wall revealed subtle enhancement after iv contrast, probably due to pyelitis.

Renal sinus cysts are common, with a prevalence between 1.28% and 1.5% [1].

Most authors distinguish between parapelvic cysts and peripelvic cysts.

Peripelvic cysts originate in sinus structures and presumably represent mostly lymphatic collections; they are often multiple, small and confluent.

Parapelvic cysts originate in the renal parenchyma and extend into the renal sinus, and are usually solitary or few in number. Although asymptomatic on most occasions, there are some reports of large parapelvic cysts causing hypertension, haematuria, and localized hydronephrosis, due to compression of the renal vasculature and/or adjacent collecting system structures.

In practice, the term renal sinus cyst is recommended to describe any fluid-filled cyst found in the renal sinus [1, 2].

In this particular case, the patient presented with urinary tract infection symptoms and with hydronephrosis on ultrasound. In this setting, it is important to search for the obstructive cause and exclude complications, with contrast enhanced CT being the modality of choice. In fact, in renal ultrasonography it can be difficult to differentiate between renal sinus cysts and hydronephrosis. To identify the existence of both entities even more.

In this case the only CT finding suggestive of inflammation/infection was a very subtle hyper-enhancement of the renal pelvis wall. More importantly, it showed a large parapelvic cyst as the cause of the calyceal dilatation.

Minimally invasive methods for the treatment of symptomatic renal sinus cysts have recently become more common, including laparoscopic decortication and ureteroscopic unroofing [3, 4].

Take Home Message
Parapelvic cyst is an unusual cause of extrinsic obstruction of the pelviureteric system.
Contrast enhanced CT scan delineates the cyst and yields a definitive diagnosis.