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 1
lists the criteria for a benign cyst. Complex cysts are often, but not uniformly, malignant (see Table 2
). They are characterisized by a series of criteria which are given in the right column of Table 1
. Figures 14


show examples.

View larger version (138K):
[in this window]
[in a new window]
|
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.
|
|

View larger version (64K):
[in this window]
[in a new window]
|
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.
|
|

View larger version (115K):
[in this window]
[in a new window]
|
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: 913914) 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
- Examine carefully every patient with renal cysts in order not to miss the diagnosis of malignancy.
- 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. 
Suggested reading
-
Barbaric Z. Principles of Genitourinary Radiology, 2nd Edition. Thieme Medical Publishers, New York, 1994
-
Koeppen-Hagemann I, Ritz E. Nierensonographie. Thieme, Stuttgart, 1992
-
Rettenmaier G, Seitz K. Sonographische Differentialdiagnostik, Bd. 1, Edition Medizin VHC, Weinheim, 1990