Multicystic dysplastic kidney

The anomaly is thought to represent the end result of hydronephrosis developing secondary to ureteric maldevelopment early in gestation. Sometimes a ureter is present, and this hydronephrotic variant is thought to represent a partial form of the condition, due to incomplete ureteric obstruction. Occasionally, only part of the kidney is affected. The Ask Upmark kidney and multilocular cystic nephroma may represent such partial segmental types of multicystic dysplastic kidney. Multicystic dysplastic kidney is second only to hydronephrosis as the cause of an abdominal mass in a neonate. Additional malformation may be present, including contralateral multicystic dysplastic kidney, contralateral ureteropelvic junction obstruction congenital, contralateral hyperplasia and horseshoe kidney. If multicystic dysplastic kidney goes undetected, it may be discovered incidentally in adulthood. It is possible that many cases of congenital absence of the kidney diagnosed in adults are due to multicystic dysplastic kidney which has involuted to the point of non-detectability.

In multicystic dysplastic kidney, plain radiographs may show a soft tissue mass, sometimes with calcification in the cyst walls. Intravenous urography shows absence of functioning renal tissue on the ipsilateral side, with compensatory hypertrophy on the contralateral side. The contralateral side should be carefully scrutinized for co-existent malformations, particularly ureteropelvic junction obstruction. Retrograde pyelography confirms absence or atresia of the ipsilateral ureter, and angiography likewise demonstrate absence or atresia of the ipsilateral renal vessels (Fig.1). Multiple thick-walled cysts of varying sizes can be demonstrated by ultrasound, CT or MRI (Fig.2). The lack of communication between the cysts is an important feature which distinguishes multicystic dysplasia kidney from severe hydronephrosis. The lack of a central large anechoic structure corresponding to a dilated renal pelvis is also a helpful discriminatory feature. In difficult cases, including the rare hydronephrotic form of multicystic dysplastic kidney, radio-isotope studies can be useful. Hydronephrotic kidneys generally display some residual function on a DMSA scan (see radionuclide renal imaging, while true multicystic dysplastic kidneys rarely demonstrate any function. Treatment is generally not indicated, unless the multicystic dysplastic kidney is causing symptoms due to size. Some have advised prophylactic nephrectomy, citing reports of an increased risk of malignancy and hypertension, but the available literature offers no proof that the incidence of either tumour or hypertension is higher in patients with retained multicystic dysplastic kidney than in normal people.

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