Multicystic dysplastic kidney

Multicystic dysplastic kidney (MCDK), also known as multicystic renal dysplasia, is a congenital condition in which one or both kidneys fail to develop normally during fetal life, resulting in a non-functioning kidney replaced by multiple cysts of varying sizes separated by dysplastic tissue. It is one of the most common causes of an abdominal mass in newborns. The condition is thought to arise from abnormal interaction between the ureteric bud and the metanephric mesenchyme during embryonic kidney development, often associated with ureteral atresia. MCDK most commonly affects only one kidney (unilateral), with the contralateral kidney typically undergoing compensatory hypertrophy to maintain normal renal function. The affected kidney lacks normal renal architecture and is essentially non-functional. In unilateral cases, most children are asymptomatic and are diagnosed prenatally through routine ultrasound screening, which reveals a kidney replaced by multiple non-communicating cysts. The affected kidney usually involutes (shrinks) over time, and many cases resolve spontaneously during childhood. However, the contralateral kidney may have associated abnormalities such as vesicoureteral reflux or ureteropelvic junction obstruction in a proportion of cases, which requires monitoring. Bilateral MCDK is incompatible with life due to the absence of functional renal tissue, leading to oligohydramnios and pulmonary hypoplasia. Management of unilateral MCDK is generally conservative, involving serial ultrasound monitoring to track involution of the affected kidney and to ensure the health and compensatory growth of the contralateral kidney. Nephrectomy (surgical removal of the affected kidney) was historically performed routinely but is now typically reserved for cases with complications such as persistent enlargement, hypertension, recurrent infections, or concern for malignancy, though the risk of malignant transformation (such as Wilms tumor) is considered extremely low. Long-term follow-up includes monitoring blood pressure and renal function, as some patients may develop hypertension or mild renal impairment over time.

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