[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/) › Chronic pyelonephritis and reflux nephropathy

# Chronic pyelonephritis and reflux nephropathy

- Lesion

Repeated infection with reflux or obstruction scars the kidney unevenly and deforms the calyces under the scars.

Updated Nov 12, 2026

## Key points

- Reflux nephropathy: the commonest form; scars at the upper and lower poles, where papillae are compound and refluxing.
- Gross: irregular, asymmetric, U-shaped cortical scars over blunted calyces.
- Micro: atrophic tubules filled with colloid-like casts (thyroidization), chronic interstitial inflammation, fibrosis.
- Glomeruli are spared at first but later develop secondary FSGS.
- Xanthogranulomatous variant: sheets of lipid-laden macrophages, may mimic renal cell carcinoma.

## What it is

Chronic pyelonephritis is tubulointerstitial inflammation and scarring with deformity of the pelvicalyceal system. Two settings produce it: reflux nephropathy, from childhood vesicoureteral reflux with infection, and chronic obstruction, which favours repeated infections. Its distinctive feature, compared with other chronic tubulointerstitial disease, is the coarse scar over a blunted, dilated calyx. Xanthogranulomatous pyelonephritis is an uncommon destructive variant with foamy macrophages, often with Proteus and staghorn stones.

## Structure

- One or both kidneys small and irregularly scarred; in contrast to vascular disease, the scars are coarse and few.
- Calyces under the scars are blunted, flattened or dilated.
- Tubules are either atrophic or dilated with pink casts resembling thyroid follicles.
- Lymphocytes, plasma cells and sometimes neutrophils in a fibrotic interstitium; arterioles thicken with hypertension.

## Paths to chronic pyelonephritis

| Setting | Mechanism | Typical findings |
| --- | --- | --- |
| [Reflux nephropathy](https://durgical.com/en/conditions/vesicoureteral-reflux/) | Infected urine refluxes into the kidney from childhood | Polar scars, often bilateral; hypertension and proteinuria later |
| [Chronic obstruction](https://durgical.com/en/conditions/hydronephrosis-and-obstructive-uropathy/) | Stasis favours recurrent infection; pressure adds atrophy | Diffuse or one-sided scarring with hydronephrosis |
| [Xanthogranulomatous pyelonephritis](https://durgical.com/en/conditions/kidney-stones/) | Chronic obstruction, often with staghorn stone and Proteus | Yellow destructive mass of foamy macrophages |

## Clinical notes

- Insidious onset of kidney insufficiency and hypertension, or found when imaging shows scars.
- Proteinuria and secondary FSGS signal a poor outcome.
- Early screening and treatment of reflux in children with urinary infection aims to prevent scarring.

## Memory aid

A scar sitting on a flat calyx tells the story of urine running uphill.

## Test yourself

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

## Which feature separates chronic pyelonephritis from other chronic tubulointerstitial diseases?

Coarse cortical scars overlying blunted or deformed calyces.

## What is thyroidization of the kidney?

Atrophic tubules filled with eosinophilic hyaline casts that resemble thyroid follicles.

## Why do reflux scars favour the poles of the kidney?

Polar papillae are often compound, with openings that let urine reflux into the parenchyma.

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## Elsewhere in DurgiPedia

- [Chronic inflammation: causes, cells and features](https://durgical.com/en/general-pathology/chronic-inflammation-causes-cells-and-features/)
- [Fibrosis in organs: TGF-β and the myofibroblast](https://durgical.com/en/general-pathology/fibrosis-in-organs-tgf-and-the-myofibroblast/)
- [Duplicated ureter, UPJ obstruction and posterior urethral valves](https://durgical.com/en/embryology/duplicated-ureter-upj-obstruction-and-posterior-urethral-valves/)

## Connections

## Related 5

- [Acute pyelonephritis](https://durgical.com/en/general-pathology/acute-pyelonephritis/)
- [Urinary tract obstruction and hydronephrosis](https://durgical.com/en/general-pathology/urinary-tract-obstruction-and-hydronephrosis/)
- [Chronic kidney disease and uremia](https://durgical.com/en/general-pathology/chronic-kidney-disease-and-uremia/)
- [Congenital anomalies of the ureter and bladder](https://durgical.com/en/general-pathology/congenital-anomalies-of-the-ureter-and-bladder/)
- [Chronic inflammation: causes, cells and features](https://durgical.com/en/general-pathology/chronic-inflammation-causes-cells-and-features/)

## Related conditions 6

- [Vesicoureteral reflux](https://durgical.com/en/conditions/vesicoureteral-reflux/)
- [Acute pyelonephritis](https://durgical.com/en/conditions/acute-pyelonephritis/)
- [Hydronephrosis and obstructive uropathy](https://durgical.com/en/conditions/hydronephrosis-and-obstructive-uropathy/)
- [Chronic kidney disease](https://durgical.com/en/conditions/chronic-kidney-disease/)
- [Kidney stones (urolithiasis)](https://durgical.com/en/conditions/kidney-stones/)
- [Posterior urethral valves](https://durgical.com/en/conditions/posterior-urethral-valves/)

## Microorganisms 1

- [Proteus mirabilis](https://durgical.com/en/microbiology/proteus-mirabilis/)

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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: [Acute Pyelonephritis](https://www.ncbi.nlm.nih.gov/books/NBK519537/) (StatPearls (NCBI Bookshelf), 2024).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

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Source: https://durgical.com/en/general-pathology/chronic-pyelonephritis-and-reflux-nephropathy/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/chronic-pyelonephritis-and-reflux-nephropathy/