Acquired renal cysts
Anna-Maria Nahm and
Eberhard Ritz
Department of Internal Medicine, Ruperto Carola University, Heidelberg, Germany
Keywords: acquired renal cysts; autosomal dominant polycystic kidney disease; carcinoma; ultrasonography
The occurrence of acquired cysts in kidneys with primary chronic renal disease, particularly tubulointerstitial diseases [13], had been known in the 19th century but was forgotten, and was rediscovered only in 1977 [4]. Cyst formation may occur even in patients with modest impairment of renal function. It is found in 1095% of patients, depending on age (more frequent in the elderly), renal function (more frequent in advanced renal failure) and duration of renal failure/dialysis therapy. While ultrasonography is an excellent screening method, small cysts and tumour formation are more sensitively detected by computed tomography (CT) scanning. It should be kept in mind, however, that with increasing age, simple renal cysts [5,6] may also develop in non-diseased kidneys, particularly in the elderly.
Acquired cysts constitute a cavity filled with fluid or semisolid debris. They result from dilatation of a segment of the nephron, either proximal or distal, lined by cuboidal or columnar epithelial cells.
Recognition of, and monitoring for, acquired renal cysts is important for two reasons. First, they may cause clinical complications (Table 1
), of which formation of adenoma, i.e. precancerous lesions, and renal cell carcinoma are the most important. Secondly, it may occasionally be difficult to differentiate between acquired renal cysts and autosomal dominant polycystic kidney disease (ADPKD). The main features that distinguish the two [5] are listed in Table 2
.
The sonographic characteristics of acquired cysts resemble those of simple renal cysts, which were described in the preceding contribution of the series [6]. Typical acquired renal cysts are shown in Figure 1
. In contrast to Figure 1
, Figure 2
shows the typical findings of early ADPKD. The important complications of tumour formation and haemorrhage are shown in Figures 3
and 4
. Some sonographic findings that are occasionally confounded with cysts are shown in Figures 5
and 6
.

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Fig. 1. An 85-year-old male patient with renal disease of unknown origin and pre-terminal renal failure. Note rarefication of renal parenchyma and presence of several small echolucent (liquid) formations, diffusely distributed throughout the cortex. These findings are typical for acquired renal cysts.
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Fig. 2. A 26-year-old male patient with a family history of ADPKD. Multiple cysts are distributed throughout the kidney. The parenchyma has higher than normal echogenicity (presumably because of microcysts below the threshold of resolution and/or vascular reflexes), but is still distinguishable (in contrast to what is found in more advanced ADPKD).
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Fig. 3. A 55-year-old male patient with biopsy-confirmed glomerulonephritis presenting with back pain and renal vein thrombosis after 26 years of haemodialysis. Between numerous small cysts, note one large cyst with lobulated inhomogeneous echodense material at the bottom of the cyst. The patient had secondary enlargement of the kidney due to acquired cysts, had developed polyglobuly, and died from renal cell carcinoma.
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Fig. 4. A 50-year-old female patient with a sudden onset of flank pain and macrohaematuria. Note the hypoechoic halonated renal mass at the lower pole of the left kidney. A CT scan with contrast-enhancement and the follow-up documented haemorrhage into a cyst.
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Fig. 5. A 38-year-old male patient. In another hospital, the diagnosis of renal cysts had been made. Iv-urographically showed megacalycosis, i.e. a developmental abnormality with pelvic enlargement. Note several echolucent (upon scanning), vaguely triangle-shaped, formations at the medulla/pyelon boundary.
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Fig. 6. A 35-year-old male patient with nephrotic syndrome secondary to focal segmental glomerulosclerosis. Note echolucent formations at the cortex/medulla boundary. To a doctor inexperienced in ultrasonography, this finding had initially created diagnostic difficulties, but the formations clearly represent relatively echolucent medullae contrasting with the echodense cortex.
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When more than one cyst is found, one should consider some of the frequent causes (Table 3
), but occasionally rarer conditions may be responsible (Table 4
) [2,7,8].
Teaching points
- In the patient with renal failure and renal cysts, the most important considerations are ADPKD and acquired cysts.
- In the patient with acquired cysts, the most important complication is development of carcinoma.
Notes
Correspondence and offprint requests to: Department of Internal Medicine, Ruperto Carola University, Heidelberg, Germany. 
References
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Noronha I, Ritz E, Bommer J, Massry SG. Acquired renal cysts. In: Massry, Glassock, eds. Textbook of Nephrology, 3rd edn. Wiliams & Wilkins, Baltimore; Vol. I, 1995: 925929
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