Introduction:
Multicystic dysplastic kidney (MCDK) is a relatively common developmental abnormality of the urinary tract. In most cases, it is an asymptomatic disease and rarely leads to problems emerging from the pressing effect of large MCDK kidneys on the adjacent organs. Nowadays, surgical intervention has mostly been replaced by a non-invasive approach with long-term follow-up.

Aim of the study:
Analysis of the diagnostic process, patients’ clinical condition, treatment, and follow-up in neonatal patients with extreme MCDK.

Material and methods:
Retrospective analysis of medical records of four infants with extreme MCDK, who were hospitalised in the Department of Intensive Therapy and Neonatal Pathology in Independent Public Clinical Hospital No. 1 in Zabrze in 2014–2019. The study also includes data from an out-patient nephrological unit, where infants are checked up by paediatric nephrologists every 6 to 12 months.

Results:
All four patients involved in this study were diagnosed during the prenatal period. After birth, the initial diagnosis was confirmed by ultrasound, X-ray, computed tomography (CT), magnetic resonance imaging (MRI), and/or scintigraphy. All patients in their neonatal period presented the symptoms caused by the pressing effect of the large size of MCDK kidneys, such as abdominal or flank discomfort, digestive disturbances, or respiratory distress. The life-threatening clinical condition of two of our patients led to surgical intervention, which significantly improved their life functions. The stable clinical condition of another two infants enabled a non-invasive approach. All four infants still remain under long-term follow-up. They are not afflicted with any problems emerging from the urinary tract and they do not require any pharmacological treatment.

Conclusions:
Despite the currently proposed non-invasive approach to MCDK, there are cases when a nephrectomy should be a considered, especially regarding patients with extreme-sized kidneys.