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Hydronephrosis

Hydronephrosis is a medical condition where the kidney becomes enlarged due to a complete or partial obstruction in the outflow of urine. This results in the dilation of parts of the kidney that function to collect urine. Hydronephrosis can affect one or both kidneys and can develop suddenly or gradually over time. This condition affects individuals of all ages including in fetuses during pregnancy.

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Plain-language summary adapted from Wikipedia. Not medical advice.