[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Kidney](https://durgical.com/en/general-pathology/areas/kidney/) › Congenital kidney anomalies

# Congenital kidney anomalies

- Lesion

Errors in kidney development or ascent produce missing, small, misplaced or fused kidneys.

Updated Nov 12, 2026

## Key points

- Bilateral agenesis: oligohydramnios, pulmonary hypoplasia, flattened face, limb deformities (Potter sequence).
- Unilateral agenesis: often silent; the single kidney may develop adaptive FSGS over decades.
- True hypoplasia: fewer renal lobes and pyramids (six or fewer); distinguish from acquired scarring.
- Ectopic kidney: usually pelvic, kinked ureter, prone to obstruction and infection.
- Horseshoe kidney: lower poles fused in most cases; ascent blocked by the inferior mesenteric artery.

## What it is

About a tenth of people are born with some anomaly of the kidney or urinary tract. Bilateral agenesis is incompatible with life and causes the oligohydramnios (Potter) sequence; unilateral agenesis is compatible with normal life, with compensatory hypertrophy of the other kidney. Hypoplasia means a small kidney with fewer lobes. Ectopic kidneys usually lie in the pelvis; horseshoe kidneys, the commonest fusion anomaly, are joined at the lower poles. Many of these anomalies obstruct urine flow and favour infection and stones.

## Structure

- Agenesis: no kidney and no ureter on that side.
- Hypoplasia: small kidney with normal architecture but fewer calyces and lobes.
- Ectopic kidney: normal or small, supplied by vessels from nearby arteries.
- Horseshoe kidney: an isthmus of renal tissue or fibrous band joins the poles in front of the aorta and vena cava.

## Clinical notes

- Horseshoe kidneys are associated with Turner syndrome and trisomy 18 and carry higher risk of stones, hydronephrosis and Wilms tumour.
- Prenatal ultrasound detects most of these anomalies.

## Memory aid

Missing, mini, misplaced or merged: the four ways the kidney can get its development wrong.

## Test yourself

Think of the answer, then tap the question to see it.

## What does bilateral renal agenesis cause in the fetus?

Oligohydramnios with the Potter sequence: pulmonary hypoplasia, facial and limb deformities.

## Which poles are usually fused in a horseshoe kidney?

The lower poles.

## What stops a horseshoe kidney from ascending?

The inferior mesenteric artery, which catches the isthmus.

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## Elsewhere in DurgiPedia

- [Kidney: pronephros, mesonephros, metanephros and ascent](https://durgical.com/en/embryology/kidney-pronephros-mesonephros-metanephros-and-ascent/)
- [Renal agenesis and the Potter sequence](https://durgical.com/en/embryology/renal-agenesis-and-the-potter-sequence/)
- [Horseshoe kidney and renal ectopia](https://durgical.com/en/embryology/horseshoe-kidney-and-renal-ectopia/)

## Connections

## Related 3

- [Cystic kidney diseases: comparison table](https://durgical.com/en/general-pathology/cystic-kidney-diseases-comparison-table/)
- [Congenital anomalies of the ureter and bladder](https://durgical.com/en/general-pathology/congenital-anomalies-of-the-ureter-and-bladder/)
- [Urinary tract obstruction and hydronephrosis](https://durgical.com/en/general-pathology/urinary-tract-obstruction-and-hydronephrosis/)

## Related conditions 3

- [Congenital kidney anomalies (horseshoe kidney, renal agenesis)](https://durgical.com/en/conditions/congenital-kidney-anomalies/)
- [Vesicoureteral reflux](https://durgical.com/en/conditions/vesicoureteral-reflux/)
- [Hydronephrosis and obstructive uropathy](https://durgical.com/en/conditions/hydronephrosis-and-obstructive-uropathy/)

[← All of general pathology](https://durgical.com/en/general-pathology/)

Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Solitary or Single-functioning Kidney - NIDDK](https://www.niddk.nih.gov/health-information/kidney-disease/solitary-kidney) (NIDDK (National Institutes of Health), 2024); [Ectopic Kidney - NIDDK](https://www.niddk.nih.gov/health-information/kidney-disease/children/ectopic-kidney) (NIDDK (National Institutes of Health), 2024); [Horseshoe Kidney - StatPearls - NCBI Bookshelf](https://www.ncbi.nlm.nih.gov/books/NBK431105/) (StatPearls Publishing (NCBI Bookshelf), 2023).

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/congenital-kidney-anomalies/