RENAL CYSTS CYSTIC DISEASE ULTRASOUND
Category: Diagnostic Radiology
Abstract : RENAL CYSTS AND CYSTIC DISEASE - Cysts The most common renal mass is a simple cyst which can be found in up to 50% of the population, the incidence increasing with age. Most cysts are asymptomatic and may be solitary or multiple. Generally they are peripheral but may occur within the kidney adjacent to the renal pelvis. A parapelvic cyst may be difficult to distinguish from pelvicalyceal dilata
RENAL CYSTS AND CYSTIC DISEASE - Cysts
The most common renal mass is a simple cyst which can be found in up to 50% of the population, the incidence increasing with age. Most cysts are asymptomatic and may be solitary or multiple. Generally they are peripheral but may occur within the kidney adjacent to the renal pelvis.
A parapelvic cyst may be difficult to distinguish from pelvicalyceal dilatation, a calyceal diverticulum or an extrarenal pelvis and careful scanning is required to differentiate. A parapelvic cyst may be the cause of a filling defect on intravenous urogram (IVU) and CT can differentiate a cyst from a diverticulum if necessary, as the latter will fill with contrast. Occasionally cysts can haemorrhage causing pain. Large cysts, particularly of the lower pole, may be palpable, prompting a request for an ultrasound scan.
Ultrasound appearances
Like cysts in any other organ, renal cysts display three basic characteristics: they are anechoic, have a thin, well-defined capsule and exhibit posterior enhancement. It can be difficult to appreciate the posterior enhancement if the hyperechoic perirenal fat lies distal to the cyst; scanning from a different angle may be helpful. Haemor-rhage or infection can give rise to low-level echoes within a cyst and in some cases the capsule may display calcification. Whilst a solitary, simple cyst can almost certainly be ignored, cysts with more complex acoustic characteristics may require further investigation, for example CT. A calcified wall may be associated with malignancy.
Autosomal dominant (adult) polycystic kidney disease (APKD)
This autosomal dominant disease has a wide spectrum of presentation. It is normally associated with progressive renal failure. A renal transplant offers a successful cure for many patients. Although in some cases APKD may cause renal failure in early life, it is also possible to achieve a normal life span with no appreciable symptoms. In about 50% of cases, cysts are present in the liver; they are also found in the spleen and pancreas in a small proportion of patients. Ultrasound screening for APKD is performed in families with a positive history, as patients may then be monitored and treated for hypertension. A negative scan does not entirely exclude disease, especially in the younger patient, and multiple examinations over years may need to be performed.
Ultrasound appearances
The disease is always bilateral, causing progressively enlarging kidneys with multiple cysts of various sizes, many having irregular margins. There is often little or no demonstrable normal renal tissue and the kidneys may become so large that they visibly distend the abdomen. APKD predisposes the patient to urinary tract infections and some of the cysts may contain lowlevel echoes as a result of infection or haemorrhage. The liver, spleen and pancreas should also be examined on ultrasound for associated cysts. A small but recognized increased incidence of tumour is recorded in patients with APKD.
Autosomal recessive (infantile) polycystic kidney disease (PCKD)
This autosomal recessive condition may often be diagnosed prenatally on ultrasound. The disease carries a high mortality rate in early childhood, and is therefore rarely seen on ultrasound in children. Tiny cysts replace both kidneys, giving them a hyperechogenic appearance due to the multiple reflections from the cyst walls and the overall increased through-transmission.
Acquired cystic disease
This condition tends to affect patients on long-term dialysis who may already have shrunken, end-stage kidneys. Its frequency increases with the duration of dialysis. Multiple cysts form in the kidneys, which may, like adult PCKD, haemorrhage or become infected. The disease tends to be more severe the longer the patient has been on dialysis. The proliferative changes which cause acquired cystic disease also give rise to small adenomata and the ultrasound appearances may be a combination of cysts and solid, hypoechoic nodules. In particular, acquired cystic disease has the potential for malignancy and it is therefore prudent to screen native kidneys, even after renal transplantation has been performed.
Multicystic dysplastic kidney (MCDK)
This is a congenital malformation of the kidney, in which the renal tissue is completely replaced by cysts. It is frequently diagnosed prenatally (although it is naturally a lethal condition if bilateral). The MCDK may shrink with age and, by adulthood, may be so small that it is difficult to detect and may be mistaken for an absent kidney. Contralateral renal hypertrophy is often present. MCDK can be associated with contralateral pelviureteric junction obstruction, which is also frequently diagnosed in utero. It is thought that MCDK occurs as a result of severe early renal obstruction during development in utero. Obstructed calyces become blocked off, forming numerous cysts which do not connect.
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