Chronic Pyelonephritis and Reflux Nephropathy

Slide 1 · Chronic Pyelonephritis

and Reflux Nephropathy

Renal tubulointerstitial pathology: mechanisms, morphology and clinical consequences

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives: Recognize and explain renal scarring

LECTURE OUTCOMES

Define chronic pyelonephritis by its tubulointerstitial and pelvocalyceal involvement.

Explain how vesicoureteral and intrarenal reflux favor polar scars.

Identify gross and microscopic hallmarks and interpret clinical consequences.

Distinguish major mimics and explain secondary glomerulosclerosis.

Core diagnostic link: Renal cortical scar + underlying deformed calyx.

Slide 3 · Chronic pyelonephritis: An anatomic definition

CORE CONCEPT

Chronic tubulointerstitial inflammation produces irreversible renal scarring.

The calyces and renal pelvis participate in the destructive process.

Calyceal involvement separates this pattern from many other interstitial nephritides.

Pelvocalyceal abnormality is part of the lesion, not an incidental imaging finding.

Slide 4 · Chronic pyelonephritis is not synonymous with all TIN

MORPHOLOGIC DISTINCTIONS

General chronic tubulointerstitial injury

Tubular atrophy and interstitial fibrosis

Can arise from numerous different etiologies

May lack characteristic calyceal damage

Chronic pyelonephritis

Tubular and interstitial injury

Irregular renal scarring

Overlying deformation of pelvis/calyces

Diagnostic specificity comes from lesion distribution and collecting-system involvement.

Slide 5 · Relationship to acute pyelonephritis

CORE CONCEPT

Acute pyelonephritis is predominantly suppurative renal infection.

Repair after acute inflammation can leave irregular cortical scars.

Persistent reflux or obstruction makes recurrent injury and scarring more likely.

Chronic disease requires a recognized scar pattern; Recurrent acute symptoms are not mandatory.

Slide 6 · The anatomic pathway: Lower tract to renal parenchyma

ANATOMIC CONTEXT

Urine passes from the kidney through the pelvis and ureter into the bladder.

The vesicoureteral junction normally limits retrograde urine flow.

Reflux can move bladder contents toward the renal pelvis and, in susceptible papillae, parenchyma.

Two distinct retrograde steps matter: Vesicoureteral reflux and intrarenal reflux.

Slide 7 · Where reflux-induced injury occurs

ANATOMIC SCHEMATIC

Vesicoureteral reflux

Backward flow from bladder toward ureter and collecting system.

Intrarenal reflux

Extension from the pelvis into papillary ducts and renal tissue.

Schematic — not a specimen or radiographic image

Schematic arrows indicate the direction of retrograde flow, not an incidence estimate.

Slide 8 · Normal antireflux mechanism

PATHOGENESIS

Oblique intramural ureter

Bladder contraction

Compression of ureteral segment

The usual ureteral insertion functions as a one-way valve during increased intravesical pressure.

Valve competence prevents urine from returning toward the kidney.

Slide 9 · Congenital predisposition to vesicoureteral reflux

PATHOGENESIS

Short intravesical ureter

Incomplete compression at voiding

Retrograde bladder urine flow

Congenital absence or shortening of the intravesical ureteral segment.

A structural valve defect allows reflux even without acquired obstruction.

Slide 10 · Congenital versus acquired reflux

ETIOLOGIC MECHANISMS

Congenital

Absent or short intravesical ureteral course

Failure of normal antireflux closure

Important in children

Acquired

Inflammation can alter ureteral contractility

Bladder dysfunction can increase residual urine

Neurogenic bladder may favor reflux and stasis

These mechanisms are source-described; They need not occur in every patient.

Slide 11 · Intrarenal reflux carries urine into the renal tissue

PATHOGENESIS

Reflux into renal pelvis

Access to papillary duct openings

Intrarenal parenchymal injury

Open ducts at papillary tips provide an intrarenal route for infected urine.

This pathway links a lower urinary tract abnormality to focal cortical scarring.

Slide 12 · Why reflux scars preferentially affect the poles

MORPHOLOGIC DISTINCTIONS

Upper and lower poles

Flattened or concave papillary tips are more common

Papillary ducts are more accessible to retrograde urine

Scars frequently cluster in polar regions

Mid-renal zones

Pointed convex papillary tips are more common

Anatomy is less favorable for intrarenal reflux

This is a tendency, not an absolute boundary

Papillary geometry helps explain the distribution of reflux nephropathy.

Slide 13 · Polar distribution of cortical injury

ANATOMIC SCHEMATIC

Upper-pole lesion

Discrete scar above a distorted calyx.

Lower-pole lesion

A second potential site for reflux-associated scarring.

Schematic — not a specimen or radiographic image

Source hallmark: Preferential upper- and lower-pole scarring with calyceal deformation.

Slide 14 · Urinary tract infection and reflux act together

CAUSAL FRAMEWORK

Ascending renal infection is more common than hematogenous spread.

Reflux provides a route for infected urine to reach the renal pelvis.

Repeated episodes of injury and healing can produce chronic scarring.

Reflux increases access; Infection supplies an inflammatory insult.

Slide 15 · Chronic scars may develop without recognized acute attacks

CORE CONCEPT

The key-concepts summary allows repeated injury with or without clinically apparent acute pyelonephritis.

A child with reflux may first be evaluated for hypertension rather than infection.

Absence of a documented febrile urinary infection does not exclude old reflux-associated scarring.

Clinical history and renal morphology may diverge.

Slide 16 · Urine outflow obstruction amplifies infection risk

PATHOGENESIS

Obstruction or voiding dysfunction

Residual urine and stasis

Bacterial multiplication

Recurrent renal injury

Examples in the source include calculi, tumors, outlet obstruction and neurogenic bladder.

Identify the underlying abnormality rather than viewing infection in isolation.

Slide 17 · Two pathways to chronic pyelonephritic damage

MORPHOLOGIC DISTINCTIONS

Reflux-associated pathway

Incompetent vesicoureteral junction

Intrarenal reflux, especially at poles

Focal polar scarring with calyceal deformation

Obstruction-associated pathway

Impaired drainage and urinary stasis

Persistent or recurrent ascending infection

Progressive cortical and collecting-system damage

Different predisposing anatomy can converge on the chronic scar pattern.

Slide 18 · From acute inflammation to a mature scar

PATHOGENESIS

Acute renal inflammation

Macrophages and lymphocytes

Tubular atrophy and fibrosis

Irregular cortical depression

The source describes replacement of neutrophils by mononuclear inflammatory cells during healing.

Reparative fibrosis produces persistent architectural distortion.

Slide 19 · Why isolated cystitis often remains below the kidney

LOCALIZATION

Bladder colonization does not automatically mean renal parenchymal infection.

In the absence of vesicoureteral reflux, infection usually remains in the bladder.

Additional susceptibility arises from obstruction, stasis or impaired host defense.

A route of spread is needed to explain progression from lower-tract infection to renal scar.

Slide 20 · Reflux nephropathy is important in children

CLINICAL CONTEXT

Children may have congenital abnormalities of the vesicoureteral junction or lower urinary tract.

Severe urinary tract abnormalities can cause lasting renal parenchymal destruction.

Hypertension evaluation may uncover renal scarring before symptomatic renal failure.

Preventable or treatable urinary tract abnormalities can precede an irreversible renal scar.

Slide 21 · Ascending infection: Source-described microbiology

ETIOLOGIC CONTEXT

Enteric gram-negative bacilli cause most urinary tract infections in the source discussion.

Escherichia coli predominates; Proteus, Klebsiella and Enterobacter are additional examples.

These organisms explain infection risk, not a unique microbial signature of chronic scars.

Histologic scarring alone does not establish the species responsible for earlier infection.

Slide 22 · Chronic pyelonephritis: Predominant tissue compartments

CORE CONCEPT

Tubules and interstitium are the principal sites of microscopic chronic injury.

Pelvocalyceal structures show accompanying inflammation, distortion or fibrosis.

Glomeruli are initially relatively preserved but may develop secondary changes.

The site and sequence of injury explain later functional findings.

Slide 23 · Characteristic gross appearance

ANATOMIC SCHEMATIC

Cortical surface

Coarse, discrete depressions and irregular contours.

Underlying collecting system

Corresponding calyceal dilatation, blunting or deformation.

Schematic — not a specimen or radiographic image

The surface scar and the distorted calyx should be interpreted together.

Slide 24 · A cortical scar is a three-dimensional lesion

GROSS MORPHOLOGY

Coarse cortical depression reflects loss of functioning renal tissue.

A discrete lesion extends through cortex toward the corticomedullary region.

The underlying calyx is dilated, blunted or distorted.

The scar–calyx relationship is more discriminating than surface irregularity alone.

Slide 25 · Calyceal blunting and papillary flattening

CORE CONCEPT

Scarred parenchyma overlies a dilated or deformed calyx.

The corresponding papilla can appear flattened.

Scarring of tissue around the calyceal epithelium contributes to structural distortion.

Papillary flattening and calyceal deformity are established morphologic hallmarks.

Slide 26 · Patchy rather than uniform renal involvement

CORE CONCEPT

Scars vary from one to several in an affected kidney.

When bilateral, scarring tends to be asymmetric.

Preserved parenchyma may separate areas of chronic injury.

Focality and asymmetry help distinguish reflux-associated scarring from diffuse processes.

Slide 27 · Chronic pyelonephritis versus chronic glomerulonephritis

MORPHOLOGIC DISTINCTIONS

Chronic pyelonephritis

Coarse, irregular, discrete surface scars

Often asymmetric bilateral involvement

Underlying calyceal dilatation or blunting

Chronic glomerulonephritis

Diffuse, relatively symmetric contracted kidneys

Scarring is not organized around deformed calyces

Glomerular disease dominates the injury pattern

Gross pattern directs the differential; Correlation with histology remains necessary.

Slide 28 · The scar–calyx correlation: A pattern-based approach

ANATOMIC SCHEMATIC

Observation

Coarse corticomedullary cortical scar.

Anatomic counterpart

Blunted/deformed calyx directly beneath.

Interpretation

Pattern supports chronic pyelonephritis/reflux-associated injury.

Schematic — not a specimen or radiographic image

Isolated interstitial fibrosis does not have the same diagnostic specificity.

Slide 29 · Tubular atrophy within scarred cortex

HISTOMORPHOLOGY — SCHEMATIC

Stylized tubular cross-sections — schematic, not histology

Chronic injury causes shrinkage and loss of normal tubules.

Atrophic tubular profiles coexist with interstitial collagen deposition.

The process is often patchy, with less-affected intervening cortex.

Tubular loss contributes directly to nephron mass reduction.

Slide 30 · Dilated and hypertrophied tubules coexist with atrophy

HISTOMORPHOLOGY — SCHEMATIC

Stylized tubular cross-sections — schematic, not histology

Remaining tubules may be enlarged or dilated.

Flattened epithelium can line distended tubular lumina.

Heterogeneous tubular calibers reflect remodeling of damaged parenchyma.

A mixed atrophic–dilated tubular pattern is typical of chronic damage.

Slide 31 · Thyroidization: A characteristic microscopic pattern

HISTOMORPHOLOGY — SCHEMATIC

Stylized tubular cross-sections — schematic, not histology

Dilated tubules may contain rounded, homogeneous proteinaceous casts.

The appearance resembles thyroid follicles filled with colloid.

Thyroidization is useful but not pathognomonic without the anatomic context.

A resemblance to thyroid tissue describes morphology, not thyroid differentiation.

Slide 32 · Interstitial fibrosis records cumulative injury

MICROSCOPIC MORPHOLOGY

Fibrous replacement extends through both cortex and medulla.

Fibrosis often surrounds atrophic or distorted tubules.

Collagenous scars accompany loss of functioning nephron segments.

Chronicity is demonstrated by fibrosis and tubular atrophy, not just inflammatory cells.

Slide 33 · Mononuclear inflammatory infiltrates

CORE CONCEPT

Chronic interstitial infiltrates accompany renal parenchymal scarring.

Lymphocytes and plasma cells are prominent after resolution of acute neutrophilic inflammation.

Inflammation may remain conspicuous even in fibrotic areas.

Inflammation and scarring frequently coexist in chronic pyelonephritis.

Slide 34 · Inflammation and fibrosis near the calyces

CORE CONCEPT

Fibrosis can involve the tissues around the calyceal epithelium.

A marked chronic inflammatory infiltrate may accompany the lesion.

This collecting-system component supports the diagnosis in the correct setting.

Calyceal alterations are not a separate, unrelated disease process.

Slide 35 · Glomeruli: Relative early preservation

CORE CONCEPT

Tubulointerstitial lesions dominate the primary injury.

Glomeruli may appear normal in relatively early or less advanced areas.

Later glomerular alterations often reflect ischemia and systemic hypertension.

Preserved glomeruli do not contradict severe adjacent tubular scarring.

Slide 36 · Ischemic glomerular alterations in advanced disease

CORE CONCEPT

Periglomerular fibrosis may develop in chronically scarred cortex.

Some glomeruli undergo fibrous obliteration.

Chronic hypertension can compound secondary glomerular injury.

Distinguish secondary glomerular lesions from a primary glomerulonephritis.

Slide 37 · How loss of renal mass leads to secondary FSGS

PATHOGENESIS

Pyelonephritic scarring

Reduced functioning nephron mass

Adaptive glomerular alteration

Secondary FSGS

The source attributes secondary FSGS to adaptive changes after substantial parenchymal loss.

Proteinuria can emerge years after the initiating renal injury.

Slide 38 · Secondary FSGS may occur after reflux has ceased

CORE CONCEPT

Significant proteinuria can arise several years after scar formation.

Continued bacterial infection or persistent reflux is not required at that late stage.

Adaptive stress on remaining glomeruli is implicated in the secondary lesion.

Current urine sterility does not negate old scarring as the origin of glomerulosclerosis.

Slide 39 · Histomorphologic reading sequence

DIAGNOSTIC COMPARISON

Compartment

Expected features

Interpretation

Tubules

Atrophy; Dilation; Thyroidization

Chronic tubular remodeling

Interstitium

Inflammation and fibrosis

Chronic scarring

Calyces

Inflammation; Pericalyceal fibrosis

Characteristic anatomic context

Glomeruli

Often spared; Later ischemia/FSGS

Usually secondary change

Report the pattern and its distribution; Do not diagnose from a single nonspecific feature.

Slide 40 · Xanthogranulomatous pyelonephritis: Distinctive variant

SPECIAL MORPHOLOGIC PATTERN

A rare form of chronic pyelonephritis.

Marked by accumulations of lipid-laden foamy macrophages.

Inflammatory admixture can include lymphocytes, plasma cells, neutrophils and giant cells.

Foamy macrophage-rich inflammation creates a striking mass-forming appearance.

Slide 41 · Associations of xanthogranulomatous inflammation

CORE CONCEPT

Frequent association with Proteus infection.

Urinary obstruction is another important accompanying condition.

Gross lesions can form large yellow–orange nodules.

The combination of obstruction, infection and macrophage-rich tissue injury is characteristic.

Slide 42 · Xanthogranulomatous lesion versus renal carcinoma

MORPHOLOGIC DISTINCTIONS

Xanthogranulomatous pyelonephritis

Yellow–orange mass-like lesion possible

Foamy macrophages with inflammatory cells

Often associated with obstruction/infection

Renal cell carcinoma

Can also present as a renal mass

Gross yellow coloration can overlap

Requires independent morphologic evaluation

A mass-like gross appearance alone cannot establish neoplasia.

Slide 43 · Chronic pyelonephritis may be clinically silent

CLINICAL PRESENTATION

Onset is often insidious rather than abrupt.

The kidney can accumulate scars before significant clinical attention.

Renal insufficiency or hypertension may be the presenting problem.

The clinical severity at detection may exceed the recent symptomatic history.

Slide 44 · Recurrent infection-type presentations

CORE CONCEPT

Some patients experience recurring episodes of fever and back pain.

Pyuria and bacteriuria may accompany active infection.

These findings alone do not quantify pre-existing chronic scarring.

Clinical activity and accumulated structural injury are different dimensions of disease.

Slide 45 · Tubular dysfunction causes polyuria and nocturia

PATHOGENESIS

Chronic tubular injury

Impaired urine concentration

Increased urine volume

Polyuria and nocturia

Loss of concentrating capacity is especially characteristic of tubulointerstitial disease.

Tubular functional symptoms may precede prominent glomerular syndromes.

Slide 46 · Hypertension can reveal childhood reflux nephropathy

CORE CONCEPT

Children with renal scars may be investigated because of elevated blood pressure.

Hypertension is a major clinical manifestation of chronic renal damage.

Secondary glomerular lesions may coexist as disease progresses.

Consider renal parenchymal scarring in the clinical evaluation of hypertension.

Slide 47 · Renal insufficiency emerges gradually

CORE CONCEPT

Progressive loss of functional parenchyma reduces renal reserve.

Azotemia or overt renal insufficiency may develop late.

Bilateral disease and reduced remaining renal mass are clinically important.

Extent of established fibrosis helps explain chronic loss of function.

Slide 48 · Urine findings: Active infection versus old scar

MORPHOLOGIC DISTINCTIONS

Current/recurrent infection

Significant bacteriuria may be present

Pyuria supports urinary inflammation

Clinical symptoms may recur

Late scarred kidney

Bacteriuria can be absent

Tubular concentrating defects may persist

Proteinuria may signal secondary glomerular injury

A negative culture does not reverse an established renal scar.

Slide 49 · Proteinuria: A change in significance over time

CORE CONCEPT

Proteinuria is usually mild in uncomplicated chronic pyelonephritic scarring.

Some patients later develop substantial proteinuria due to secondary FSGS.

Proteinuria may reach the nephrotic range in this subgroup.

Heavy proteinuria should prompt assessment for superimposed adaptive glomerular injury.

Slide 50 · Why new proteinuria is prognostically important

CORE CONCEPT

Onset of significant proteinuria can indicate secondary FSGS.

This change to an increased likelihood of progression to end-stage kidney disease.

The prognostic inference comes from glomerular damage superimposed on pre-existing scarring.

A late glomerular phenotype changes the risk profile of a primarily tubulointerstitial disease.

Slide 51 · Imaging correlates of established scarring

ANATOMIC SCHEMATIC

Renal size and contour

Asymmetric contracted kidneys; Coarse cortical scars.

Collecting system

Calyceal blunting and deformation beneath the scars.

Schematic — not a specimen or radiographic image

Radiologic identification relies on the combined parenchymal and calyceal pattern.

Slide 52 · Demonstrating reflux is not the same as detecting scars

DIAGNOSTIC REASONING

Voiding cystourethrography can demonstrate retrograde passage of contrast.

Renal imaging may instead show old cortical scars and calyceal deformation.

Current reflux may have resolved when chronic parenchymal consequences are discovered.

Tests answer different questions: Active reflux versus residual damage.

Slide 53 · Diagnostic pattern recognition at a glance

DIAGNOSTIC COMPARISON

Finding

Supports

Important qualification

Polar cortical scars

Reflux-associated chronic injury

Not exclusive to reflux

Blunted/deformed calyces

Chronic pyelonephritic pattern

Also seen with analgesic nephropathy

Tubular thyroidization

Chronic tubulointerstitial damage

Not independently specific

Late heavy proteinuria

Secondary FSGS possible

Other glomerular causes need evaluation

Integrate imaging, anatomy, history, and tissue findings rather than using one feature.

Slide 54 · Calyceal injury: Chronic pyelonephritis and analgesic nephropathy

MORPHOLOGIC DISTINCTIONS

Chronic pyelonephritis

Reflux/obstruction often present

Coarse polar corticomedullary scars

Blunting of underlying calyces

Analgesic nephropathy

Drug-related tubulointerstitial damage

May also damage papillae and calyces

Requires separate exposure and morphologic context

Both entities as important causes of calyceal involvement.

Slide 55 · Distinguish primary interstitial disease from chronic GN

MORPHOLOGIC DISTINCTIONS

Tubulointerstitial-predominant injury

Concentrating defects; Nocturia/polyuria

Tubular atrophy, interstitial fibrosis

Characteristic calyceal changes if pyelonephritic

Primary glomerular disease

Dominant glomerular syndrome may be present

Glomerular lesion drives initial kidney injury

May secondarily cause tubulointerstitial scarring

Advanced renal disease can blur the clinical distinction.

Slide 56 · Anatomic and etiologic differential diagnosis

DIAGNOSTIC PITFALLS

Tubulointerstitial fibrosis by itself is not specific for reflux nephropathy.

Drug or toxin injury can also cause chronic interstitial disease.

Calyceal deformity plus reflux/obstruction history strengthens the attribution.

Avoid inferring a single past cause from a nonspecific microscopic scar.

Slide 57 · Case: A child investigated for hypertension

CLINICOPATHOLOGIC APPLICATION

Clinical vignette

School-age child with hypertension and an asymmetrically small kidney.

Imaging identifies a polar cortical scar above a blunted calyx.

Interpret the findings

Which renal disorder is favored?

What urinary tract abnormality may explain the distribution?

Teaching interpretation

Pattern supports reflux-associated chronic pyelonephritic scarring.

Vesicoureteral and intrarenal reflux provide the anatomic mechanism.

Slide 58 · Case: Thyroidization on a renal biopsy

CLINICOPATHOLOGIC APPLICATION

Clinical vignette

Renal cortex shows tubular atrophy, dilated tubules with proteinaceous casts, and fibrosis.

The biopsy lacks evidence about the collecting system.

Interpret the findings

Does thyroidization alone prove reflux nephropathy?

What other correlation is needed?

Teaching interpretation

No; Thyroidization indicates chronic tubular damage.

Seek radiologic calyceal deformity and relevant urinary tract history.

Slide 59 · Case: Proteinuria long after childhood infection

CLINICOPATHOLOGIC APPLICATION

Clinical vignette

Adult with a previously scarred kidney; Now substantial proteinuria.

Current urine culture is negative and reflux is no longer documented.

Interpret the findings

Why might proteinuria have increased?

Does absence of present infection exclude the mechanism?

Teaching interpretation

Secondary adaptive FSGS can follow loss of renal mass.

It may occur without ongoing reflux or infection.

Slide 60 · Mechanistic synthesis: From reflux to renal scarring

INTEGRATION

Vesicoureteral reflux makes retrograde urine flow possible.

Intrarenal reflux preferentially exposes papillary ducts at the upper and lower poles.

Recurring injury and repair leave irregular cortical and calyceal scars.

Chronic tubular and glomerular dysfunction then shape later manifestations.

Mechanism → distribution → morphology → clinical phenotype.

Slide 61 · Morphologic synthesis: The decisive pattern

INTEGRATION

Gross: Irregular coarse corticomedullary scars, often polar and asymmetric.

Collecting system: Underlying calyceal blunting/deformity and papillary flattening.

Microscopy: Tubular atrophy/dilatation, thyroidization, fibrosis and chronic inflammation.

Glomeruli: Early relative preservation with later ischemia or secondary FSGS.

Read anatomy and histology as one connected lesion.

Slide 62 · Clinical synthesis: What the renal scar predicts

INTEGRATION

The onset may be silent or involve recurrent infection-like episodes.

Tubular dysfunction causes impaired concentrating ability, polyuria and nocturia.

Hypertension and renal insufficiency may bring patients to medical attention.

New substantial proteinuria suggests secondary glomerular involvement and worse prognosis.

Clinical decline can continue after reflux or bacteriuria is no longer demonstrable.

Slide 63 · Primary source and reading context

REFERENCE

Robbins, Cotran & Kumar: Pathologic Basis of Disease

11th edition (2026), Chapter 20: The Kidney

“Chronic Pyelonephritis and Reflux Nephropathy,” pp. 844–845.

Related section: “Pyelonephritis and Urinary Tract Infection,” pp. 840–844.

Relevant original textbook figures: 20.25–20.26 (not reproduced in this deck).

Conceptual anatomical and microscopic drawings in this lecture are original schematics, not clinical images.