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Nephrol Dial Transplant (2000) 15: 1702-1704
© 2000 European Renal Association-European Dialysis and Transplant Association

Renal Ultrasonography Lesson

The simple renal cyst

Anna-Maria Nahm and Eberhard Ritz

Department Internal Medicine, Ruperto Carola University Heidelberg, Germany

Simple renal cysts are frequent, particularly in the elderly. Fifty per cent of individuals over 50 years of age have single or multiple cysts. Every cystic mass must be evaluated by sections in two planes. The examination must provide an exact evaluation of localization, form, size and structure.

The differentiation of simple renal cysts from aquired cystic renal disease will be discussed in the next contribution of this series.

The main concern is the distinction between benign cysts and malignancy. The left column of the Table 1Go lists the criteria for a benign cyst. Complex cysts are often, but not uniformly, malignant (see Table 2Go). They are characterisized by a series of criteria which are given in the right column of Table 1Go. Figures 1–4GoGoGoGo show examples.


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  		Table 1. Characteristics of benign and complex renal cysts

 

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  		Table 2. The conditions which must be considered in the differential diagnosis of complex cysts

 


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  		Fig. 1. (a) Typical appearance of a simple renal cyst at the upper pole of the right kidney. Note the hypoechoic mass with through transmission, absent internal echoes and sharply demarcated posterior wall. (b) Indistinctly demarcated hypoechoic mass at the upper pole of the left kidney! One year before it had been described as a cyst of small size. The final diagnosis was renal cell carcinoma.

 


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  		Fig. 2. A cyst of the left kidney expanding into the renal sinus.

 


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  		Fig. 3. Clearly delineated echolucent mass with through transmission, but also with internal echoes. (a) Circumscribed area of echosignals within an otherwise echolucent cyst. The final diagnosis was a haemorrhagic cyst. (b) An oval hypoechoic formation which had been present for several years but grown in size and increased in echogenicity. The final diagnosis was gelatinous carcinoma.

 


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  		Fig. 4. (a) A hypoechoic renal mass in a patient with sudden onset of flank pain and macrohaematuria. (b) The CT-scan with contrast enhancement documents the presence of a cyst with high density (Hounsfield units corresponding to blood). (c) Same formation 2 days later, after another episode of macrohaematuria. (d) Same formation 3 weeks later. Note minute hypoechoic formation corresponding to a small residual cyst.

 
Benign cysts must be distinguished from sinus cysts, pelviectasis and urinary tract obstruction (see Nephrol Dial Transplant 2000; 15: 913–914) as well as from masses, lymphomas or cysts in the neigbouring organs: pancreas, spleen, adrenal gland, retroperitoneum.

It is important to emphasize that not all complex cysts can be reliably be diagnosed using ultrasonography alone. More definite studies, such as thin-cut CT (with enhancement), or MRT are then indicated.

Teaching points

  1. Examine carefully every patient with renal cysts in order not to miss the diagnosis of malignancy.
  2. In the symptomatic patient with cysts think of complications e.g. haemorrhage, abscess.

Notes

Correspondence and offprint requests to: E. Ritz, Department of Renal Medicine, University of Heidelberg, Bergheimer Strasse 58, D-69115 Heidelberg, Germany. Back

Suggested reading

  1. Barbaric Z. Principles of Genitourinary Radiology, 2nd Edition. Thieme Medical Publishers, New York, 1994
  2. Koeppen-Hagemann I, Ritz E. Nierensonographie. Thieme, Stuttgart, 1992
  3. Rettenmaier G, Seitz K. Sonographische Differentialdiagnostik, Bd. 1, Edition Medizin – VHC, Weinheim, 1990

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