The renal sinus cystthe great imitator
Anna-Maria Nahm and
Eberhard Ritz
Department Internal Medicine, Ruperto Carola University Heidelberg, Heidelberg, Germany
Many colleagues who perform renal ultrasonography are confronted with cases that present difficulties to differentiate particularly between renal sinus cysts and obstruction. It is therefore useful to discuss the diagnostic criteria of renal sinus cysts and to examine some conditions which have to be considered in the differential diagnosis.
Little histological documentation is available. Most authors distinguish:
- (i) parapelvic cysts: originating in the renal parenchyma extending into, and primarily expanding within, the renal sinus, and
- (ii) peripelvic cysts: originating in sinus structures which presumably represent mostly lymphatic collections.
If one finds echolucent structures in the renal sinus, which points argue for renal sinus cysts?
Typical renal sinus cysts are
- oval (seldom perfectly round)
- sharply delineated
- echo-free/hypoechoic
- usually multiple
- oriented in a radial direction towards the hilus
- not interconnected.
In order to verify that the structures are oriented in a radial direction towards the hilus, it is necessary to scan the sinus region. The two signs most helpful for differentiation between sinus cysts and pelvic/calyceal dilatation are the following: (i) renal sinus cysts are never interconnected and (ii) the echolucency cannot be traced down to the ureter. Figure 1
illustrates the difficulty of differential diagnosis.

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Fig. 1. A 43-year-old female with a long standing history of urinary tract infection was admitted. The diagnosis of the referring physician was sinus cysts. (a) A quick first scan shows a series of roundish, echolucent structures without interconnectioncompatible with the diagnosis of sinus cysts. (b) Detailed examination, taking serial sweeps, however, shows that the structures are clearly connected with the pelvis. The final diagnosis, confirmed by i.v. urography, was pelviureteral stenosis with pelvicalyceal dilatation.
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Which differential diagnoses have to be considered?
- Urinary tract obstruction.
- Ampullary pelvis and ectasia of calyces and pelvis during pregnancy, diabetes mellitus and other states of high urinary flow rate.
- Sinus lipomatosis (lipomas are echogenic in contrast to echolucent cysts, but the distinction has very little practical importance).
- Isolated calyceal cysts, hydrocalyces megacalicosis and calyceal diverticulae.
- Haematoma, loculated urinoma.
- Dilated veins in the hilus region, renal artery aneurysm, arteriovenous malformation.
- Benign cystic lymphangioma, renal sinus angiomyolipoma, uroepithelial or renal carcinoma.
When the diagnosis remains doubtful, further imaging modalities should be considered, e.g. urography, CT, MR imaging.
In order to distinguish physiological from pathological conditions it is useful to consider the size limits of normal structures:
- calyceal diameter <10 mm
- diameter of pyelon in sagittal direction <15 mm.
In the patient with borderline findings it is helpful (i) to compare the sinus structures of the two kidneys and (ii) to examine the patient in supine and upright positions to exclude confounding effects of dilatation from high urine flow.
Examples diagnosis in three patients are given in Figures 24

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Fig. 2. A 58-year-old patient with known vesicoureteral reflux and recurrent urinary tract infection. Admission because of suspected obstruction. Note numerous oval echolucent structures directed towards the centre of the hilus which are not interconnected. The final diagnosis was renal sinus cysts.
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Fig. 3. A 68-year-old male patient with a history of nephrolithiasis. The scan shows multiple roundish echolucent formations. Note that, in contrast to Fig. 2 , a narrow interconnection (arrow) is demonstrable between the oval hyperechoic structure and the renal pelvis. In this case, the final diagnosis is hydrocalyx, presumably secondary to stone-induced scarring of the calyceal infundibulum (renal tuberculosis had been excluded).
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Fig. 4. A 68-year-old male patient with known uroepithelial carcinoma of the bladder. Six weeks previously a neobladder had been created surgically. The patient was admitted because the physician in charge was unable to decide whether cysts or obstruction were present. (a) Echolucent pyramidoid formations which show no connections with the pelvis. (b) A different section, however, clearly shows a connection between the hyperechoic formation and the pelvis. The final diagnosis was obstruction.
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Teaching Point
If you see hypoechoic structures in the renal sinus, the most important points arguing for the diagnosis of sinus cysts are:
- ovaloid form
- orientation towards the renal hilus
- lack of interconnection between the structures.
Notes
Correspondence and offprint requests to: Prof. E. Ritz, Sektion Nephrologie, Med. Universitätsklinik, Bergheimer Str. 56a, D-69115 Heidelberg, Germany. 
Suggested reading
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Barbaric Z. Principles of Genitourinary Radiology, 2nd Edition. Thieme Medical Publishers, New York, 1994
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Koeppen-Hagemann I., Ritz E. Nierensonographie. Thieme, Stuttgart, 1992
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Rettenmaier G, Seitz K. Sonographische Differentialdiagnostik, Bd. 1. Edition medizinVHC, Weinheim, 1990