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PubMed This is a summary of 16 peer-reviewed journal articles Updated
Pediatric Nephrology

The Biology of Growth: How Renal Dysplasia Develops

At a Glance

Renal dysplasia happens when signals between fetal kidney tissues are interrupted, causing disorganized, cystic kidneys. Unilateral dysplasia affects one kidney and usually has an excellent prognosis, while bilateral dysplasia affects both and can be severely life-limiting.

To understand how renal dysplasia develops, it helps to think of kidney growth as a complex “handshake” between two different tissues in the developing fetus. When this handshake is interrupted, the kidney does not form correctly, leading to the various types of renal abnormalities parents often hear about [1][2][3].

The Biology of the “Kidney Handshake”

Early in pregnancy, two structures must meet and communicate to create a functioning kidney:

  1. The Ureteric Bud: This eventually becomes the “plumbing” system (the ureter and collecting ducts) [1][3].
  2. The Metanephric Mesenchyme: This tissue eventually becomes the “filters” (the nephrons) that clean the blood [1][3].

For a healthy kidney to grow, these two must send signals back and forth in a process called reciprocal induction. If these signals are interrupted or blocked—perhaps by a tiny genetic variation or miscommunication in the cellular signals—the tissue doesn’t develop into filters [1][4]. Instead, it may form disorganized structures, primitive ducts, or fluid-filled cysts [3][5].

Dysplasia vs. Hypoplasia: What’s the Difference?

Doctors use specific terms to describe exactly how the kidney development went off-track:

  • Renal Dysplasia: This means the tissue is “disorganized.” The kidney hasn’t just failed to grow; it has grown the wrong way, often resulting in cysts or primitive, non-working tissue [3][5].
  • Multicystic Dysplastic Kidney (MCDK): This is a severe form of dysplasia where the entire kidney is replaced by non-communicating cysts and has no function [3][6].
  • Renal Hypoplasia: This means the kidney is “small but normal.” It has the correct architecture and works fine, but it simply has fewer filtering units (nephrons) than a standard kidney [3][5].

Unilateral vs. Bilateral: A Critical Distinction

The most important factor in your child’s prognosis is whether one kidney or both are affected.

Unilateral Dysplasia (One Side)

This is the most common form [7][8]. Because the other kidney is healthy, it performs a process called compensatory hypertrophy [9][10].

  • Picking up the Slack: The healthy kidney grows larger than average to handle the filtration needs of the whole body [9][11].
  • Healthy Pregnancy: Since the one healthy kidney produces enough urine, the levels of amniotic fluid (the “cushion” around the baby) remain normal during pregnancy.
  • Excellent Outlook: Children with one healthy kidney generally live normal, healthy lives [12][13].

Bilateral Dysplasia (Both Sides)

This is a much rarer and far more serious condition. If both kidneys are dysplastic, they cannot produce enough urine while the baby is in the womb [12][7].

  • Oligohydramnios: This term refers to severely low amniotic fluid. Because amniotic fluid is mostly fetal urine, low levels indicate the kidneys aren’t working well [12][7].
  • Lung Development and Prognosis: Amniotic fluid is vital for fetal lung development. Severe bilateral dysplasia is often a life-limiting or fatal condition in the neonatal period (sometimes called Potter Sequence) because the baby’s lungs do not mature enough to support breathing outside the womb [7][14]. Survival in bilateral cases depends entirely on whether there is enough residual kidney function to produce amniotic fluid and support postnatal life [15][16].

Common questions in this guide

What is the difference between renal dysplasia and hypoplasia?
Renal dysplasia means the kidney tissue is disorganized and often filled with non-working cysts. Renal hypoplasia means the kidney has normal structure and works fine, but is simply smaller and has fewer filtering units than average.
What happens if my baby has unilateral renal dysplasia?
In unilateral dysplasia, only one kidney is affected. The healthy kidney usually grows larger than average to do the work of both kidneys, a process called compensatory hypertrophy. Most children with this condition live normal, healthy lives.
Why is amniotic fluid important in renal dysplasia?
Amniotic fluid is mostly made of fetal urine. If a baby has bilateral renal dysplasia, their kidneys cannot produce enough urine, leading to severely low amniotic fluid. This fluid is absolutely essential for the baby's lungs to develop properly before birth.
What is a multicystic dysplastic kidney (MCDK)?
MCDK is a severe form of renal dysplasia where the entire kidney is replaced by cysts and has no function. If this only affects one kidney and the other is healthy, the healthy kidney will compensate to meet the body's needs.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Can you explain the difference between my child's dysplasia and a hypoplastic kidney?
  2. 2.Is the 'healthy' kidney showing signs of compensatory hypertrophy on current scans?
  3. 3.Were there any signs of low amniotic fluid (oligohydramnios) during the pregnancy?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (16)
  1. 1

    Renal cystic diseases during the perinatal and neonatal period.

    Raina R, DeCoy M, Chakraborty R, et al.

    Journal of neonatal-perinatal medicine 2021; (14(2)):163-176 doi:10.3233/NPM-200520.

    PMID: 32986687
  2. 2

    Supporting Infants with Multicystic Dysplastic Kidney Disease: A Comprehensive Approach.

    Baker HM, Jnah AJ

    Neonatal network : NN 2024; (43(5)):286-294 doi:10.1891/NN-2024-0007.

    PMID: 39433342
  3. 3

    Practical Approach to Congenital Anomalies of the Kidneys: Focus on Anomalies With Insufficient or Abnormal Nephron Development: Renal Dysplasia, Renal Hypoplasia, and Renal Tubular Dysgenesis.

    Gazeu A, Collardeau-Frachon S

    Pediatric and developmental pathology : the official journal of the Society for Pediatric Pathology and the Paediatric Pathology Society 2024; (27(5)):459-493 doi:10.1177/10935266241239241.

    PMID: 39270126
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    High Activation of the AKT Pathway in Human Multicystic Renal Dysplasia.

    Apostolou A, Poreau B, Delrieu L, et al.

    Pathobiology : journal of immunopathology, molecular and cellular biology 2020; (87(5)):302-310 doi:10.1159/000509152.

    PMID: 32927453
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    Renal dysplasia development and chronic kidney disease.

    Zhang L, Yang C, Liu X, et al.

    Pediatric research 2025; (98(4)):1212-1222 doi:10.1038/s41390-025-03950-0.

    PMID: 40000855
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    Single-Center Experience of Pediatric Cystic Kidney Disease and Literature Review.

    Grlić S, Gregurović V, Martinić M, et al.

    Children (Basel, Switzerland) 2024; (11(4)) doi:10.3390/children11040392.

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    Predictors of poor neonatal outcomes in fetuses diagnosed with congenital urinary tract anomalie.

    Pop-Trajkovic Dinic S, Zivadinovic R, Stefanovic M, et al.

    Ginekologia polska 2021; doi:10.5603/GP.a2021.0032.

    PMID: 33844244
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    Diagnostic accuracy of midtrimester antenatal ultrasound for multicystic dysplastic kidneys.

    Scala C, McDonnell S, Murphy F, et al.

    Ultrasound in obstetrics & gynecology : the official journal of the International Society of Ultrasound in Obstetrics and Gynecology 2017; (50(4)):464-469 doi:10.1002/uog.17305.

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    Natural History of Contralateral Hypertrophy in Patients with Multicystic Dysplastic Kidneys.

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    The Journal of urology 2018; (199(1)):280-286 doi:10.1016/j.juro.2017.06.075.

    PMID: 28645868
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    The Incidence and Durability of Compensatory Hypertrophy in Pediatric Patients with Solitary Kidneys.

    Wang MK, Gaither T, Phelps A, et al.

    Urology 2019; (129()):188-193 doi:10.1016/j.urology.2019.04.003.

    PMID: 30986483
  11. 11

    Multicystic Dysplastic Kidney: Prenatal Compensatory Renal Growth Pattern.

    Gilad N, Weissmann-Brenner A, Gilboa Y, et al.

    Journal of ultrasound in medicine : official journal of the American Institute of Ultrasound in Medicine 2021; (40(10)):2165-2171 doi:10.1002/jum.15605.

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    Prenatal diagnosis to postnatal outcomes in multicystic dysplastic kidney: experience of a tertiary center in the Black Sea region.

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    Clinical outcome of children with prenatally diagnosed isolated unilateral multicystic dysplastic kidney.

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    Bilateral multicystic dysplastic kidney disease in a Fetus: A rare case with a fatal outcome.

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    From Intermittent Knee Pain to End-Stage Kidney Disease: An Atypical Presentation of Bilateral Kidney Dysplasia in an 11-Year-Old Girl.

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    PMID: 40927561

This page explains the biological development of renal dysplasia for educational purposes. Always consult your pediatric nephrologist or maternal-fetal medicine specialist for specific medical advice regarding your child's pregnancy and prognosis.

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