Basics of renal pathology

Hafez M. Bazaraa

Juan RosaiItalian American (1940)

Pathology, the parent discipline, started withphysicians doing autopsies [on their patients] during the Renaissance in Italy... to try to understand the reasons for the symptoms and the signs that they had beenmonitoring

Marcello MalpighiEarliest descriptions of renal microanatomy Based on his observations with the newly developed microscope (1666)Urine formed in kidney, filtration mechanism between blood & tubules

Giovanni Battista Morgagni (1682) Related PM & clinical findings Refused to rely on microscopic examination

REN

AL

PATH

OLO

GY

William Bowman (1816–1892)English physician OphthalmologistDescribed components of the proximal nephron & periglomerular capsule Tubule Schematic representation

of Nephron (Bowman)

Epithelial Cells

Podocytes

endotheliumB.M.

Filtration barrier

Cells: endothelial, epithelial, mesangial

Back to 19th Century

Edema (Dropsy) Hypertension Hematuria Oliguria Albuminuria Uremia Well described Underlying processes still not clear

Friedrich Gustav Jakob Henle(1809–1885) Berlin, Zurich, Heidelbergdissected the microanatomy of the

kidney (and many other organs)discovered the tubular segment

(loop of Henle)the Henle–Koch postulates

Theodor Fahr (1877–1945) Hamburg & Paristhe first modern renal pathologistdocumented pathological changes in

renal tissue relating these to clinical expression

of renal diseasewith the internist Franz Volhard

1950s

The renal needle biopsy Aspiration first used by Nils Alwall from Sweden

(1944) 13 patients, 1 death, stopped, published 1952 Cutting needle The pathology world was at first hostile to the idea

of a tiny specimen to diagnose

300 yrs after Malpighi

Immunofluorescence microscopy to detect tissue-bound immune deposits (Coons and Kaplan, 1950)

Electron microscopy The first observations of ultrastructural changes in glomerular disease (1957)

Epithelial and Basement membrane changes require E/M

Thick BM:-Diabetic nephropathy-Alport (silver irregular) -Chronic TMA (silver splitting)-Deposits*Membranous (subepithelial) *Amyloid*MPGN (subendothelial) *Immunotactoid

Yet pathology is never alone ….

DISEASE

Small doctors treat findings, Average doctors treat diseases,Great doctors treat patients

I’m not a pathologist

Clinical condition

Biopsy

Specimen examined

Pathology report

Clinical conditions

SRNS AKI & RPGN Hematuria & proteinuria Secondary nephropathies CKD Transplantation

What is adequate?

2 Cores 10 Glomeruli 2 Arteries 3 (1) Glomeruli for IF 1 Glomerulus for EM

+ Clinical data+ timing+ sample handling

Fix in 10% Neutral (buffered) formalin-Cheap & available-Suitable for all stains & IHC (but NOT IF)-Reversible (can transfer to other fixative for E/M)

Stains

Hx&E PAS B.M. & Mesangial matrix

Masson TrichromeFibrosis

Silver B.M. & Mesangial matrix

Congo redAmyloid

Martius Scarlet Blue(MSB) Fibrin

Immunofluorescence

Performed on unfixed, frozen sections: IgG, IgM and IgA C3, C1q, and C4 C4d in allograft biopsies Others:

– fibrin– kappa and lambda light chains– collagen IV alpha chains – virus identification– lymphocyte phenotyping in allografts in suspected

PTLD

In-situ hybridization

Uses labeled cDNA or RNA probes It localizes specific DNA/RNA sequence in

tissue section The commonly used:

– BK virus.– EB virus probes in the diagnosis of PTLD.– Pathogenic cytokines such as platelet-derived

growth factor, epithelial growth factor, etc.

Electron Microscopy

“Electron microscopy provides essential or helpful information to a substantial fraction (50-60%) of cases, and whether a biopsy will fall into the latter fraction is not apparent from the clinical history”

Haas M, 2007

Reembedding of tissue for E/M possible but not the best thing to do

Electron Microscopy

Thin GBM nephropathy Alport nephropathy Recurrence of focal segmental sclerosis Staging membranous nephropathy Dense deposit disease (MPG type II) Cryoglobulinemic glomerulopathies Early diabetic changes Fabry´s disease Immunotactoid nephropathy

Most valuable with Hematuria, Familial conditions & also proteinuria with normal KF

What to look at?

Glomeruli Glomerular pathology:

– Cellularity– Inflammation– Scarring– Abnormal deposits– GBM changes

Tubules

• Tubular pathology :

– Cellular injury

– Inflammation

– Atrophy

– Casts

Interstitium

• Interstitial pathology:

– Cellular infiltrates

– Edema/fibrosis

Vascular disease

• Vascular pathology:

– Inflammation

– Thrombosis– Hyalinosis

– Sclerosis

CLINICAL

-Nephrotic syndrome

-Isolated proteinuria

-Recurrent/ persistent Hematuria

-Glomerulonephritis

-RPGN

PATHOLOGICAL•Minimal change•Focal/ diffuse mesangial•Membranous•MPGN•Focal/ diffuse proliferative•Crescenteric•FSGS

Diffuse proliferative GN

Crescenteric GN:Proliferating & infl. Cells fill Space

Cellular Fibrocellular Fibrous

Crescenteric GN:Proliferating & infl. Cells fill Space

RPGN

•Rapidly-progressive renal failure•GlomerularNOT vascular (TMA, APL, RVT)NOT tubulointerstitialNOT pre or post renal

Type 1

AntiGBM

Linear IF; IgG

-Goodpasture (+ pulm hge)

-AntiGBM nephritis

Type 2

Immune complex

Granular IF-IgAN/HSP-PSGN-MPGN-MembGN-SLE-Cryoglobulinemia

Type 3

Pauci-Immune

No IFANCA +ve-Wagener-Microscopic polyangitis-Churg Straus-Renal limited

Type 4 : double Ab ANCA-ve, idiopathic, type5

Proliferative GN (cellular lesions)

Diffuse proliferative Crescenteric Focal proliferative Mesangioproliferative Membranoproliferative

Focal Proliferative

Focal Mesangial

Mesangial

IgA

Double contour

Peripheral migration and interposition of mesangium: Mesangial cells and often matrix extend from the central lobular portion of the tuft into the peripheral capillary wall.

Migrating between endothelial cell and basement membrane and causing capillary wall thickening with two layers of extracellular matrix.

This two-layer or double contour appearance may involve a few or all capillaries.

-ve ?TMA

DDD (MPGN II)

Membranous

Diffuse= affects all/ most glomeruli Focal= affects some (<50%) glomeruli Global= affects all of the involved glomerulus Segmental= affects part of the involved

glomerulus

FSGS

Glomerulosclerosis

Scarring glomerular lesion Obliterated capillaries & solidified tuft ↑ Extracellular matrix ± Obliterated space by collagen=Hyalinosis (old imprecise term)Vs Fibrosis (healed necrotizing ; PAS-ve,

lesion)

FSGS: pattern of injury; Diverse Causes

Idiopathic sporadic Genetic Drugs (CNI, Li, IFNalpha, Pamidronate, Heroin, ..) Viral (HIV, Parvo, ..) Adaptive responses

– ↓renal mass: unilat. Agenesis, dysplasia, reflux nephropathy, progressive CKD

– DM, HTN, obesity, sickle, CCHD Renal scarring pattern: TMA. Focal proliferative,

Membranous, Alport, …

FSGS: subtypes

NOS Segmental sclerosis Typical

Collapsing Tuft collapse, epithelial hyperplasia

Worse

Cellular Endocapillary proliferation & usu. epithelial hyperplasia

Early

Tip Tuft sclerosis at prox. Tubule pole

Better

Perihilar Tuft sclerosis at vascular pole

May be 2ry

Obsolescent (globally sclerotic) glomeruli

Glomeruli Glomerular pathology:

– Cellularity– Inflammation– Scarring– Abnormal deposits– GBM changes

Tubules

• Tubular pathology :

– Cellular injury

– Inflammation

– Atrophy

– Casts

Interstitium

• Interstitial pathology:

– Cellular infiltrates

– Edema/fibrosis

Vascular disease

• Vascular pathology:

– Inflammation

– Thrombosis– Hyalinosis

– Sclerosis

Vascular

InflammationVasculitis, Rejection HyalinosisAgeing, DM, HTN, CNI (isometric vacuolization) ThrombosisTMA, PSS, Malignant HTN, emboli, … Sclerosis: HTN

TMA: traditional views

It is a specific disease It is uncommon It is an acute condition It is always associated with HUS or TTP

•IT IS A COMMON PATTERN OF INJURYwith many potential causes/ complement activation patterns•Acute & chronic forms, some very subtle

Glomeruli Glomerular pathology:

– Cellularity– Inflammation– Scarring– Abnormal deposits– GBM changes

Tubules

• Tubular pathology :

– Cellular injury

– Inflammation

– Atrophy

– Casts

Interstitium

• Interstitial pathology:

– Cellular infiltrates

– Edema/fibrosis

Vascular disease

• Vascular pathology:

– Inflammation

– Thrombosis– Hyalinosis

– Sclerosis

Tubulointerstitial

ATN/ ATI (ischemic or toxic) Epithelial degeneration/ necrosis NO inflammation vs Interstitial Nephritis

Acute interstial nephritis

NPHPCysts arise from CM junction of normal-sized kidneys. N size, ↑echog, ↓CM diff, CM cysts

Histological triad-Tubular (& glom) cysts-Tubular membrane disruption-Tubulointerstitial infl. & fibrosis

Hildebrandt et al.

JASN 2007

IFTA

Active and chronic lesions

Vascular sclerosis Glomerular sclerosis Fibrous crescents Tubular atrophy Interstitial fibrosis

amyloid

TRANSPLANTATIONHyperacute rejection

Banff classification

Category 1: Normal biopsy or nonspecific changes

Category 2: Antibody-mediated changes Category 3: Borderline changes Category 4: TCMR Category 5: Interstitial fibrosis and tubular

atrophy Category 6: Other changes not considered to

be caused by acute or chronic rejection

Borderline & acute TCMRTCMR Tubulitis Interstitial Infl. ArteritisBorderline/ suspicious

Foci t1-3 Minor i0-1 NONEMild t1 i 2-3

Grade Ia Foci t2 i 2-3 in >25% of non-sclerotic cortex

Grade Ib Foci t3

Grade II ± ± Intimal arteritisIIa V1 (mild-mod)IIb V2 (severe >25%

luminal area)Grade III V3 Transmural arteritis and/or arterial fibrinoid

change and necrosis of medial smooth muscle cells with lymphocytic inflammation

Chronic active TCMR

Chronic allograft arteriopathy

Borderline, acute & chronic TCMR

Cellular rejection

Intimal arteritis

Transmural arteritis & C4d

Acute ABMR

glomerulitis

Double contours

Acute/ Active ABMR

Histological evidence of acute tissue injury;any of: arteritis, microvasvular infl. (G &/or ptc), acute TMA, acute tubular injury

Evidence of current/recent antibody interaction with vascular endothelium ;any of: Linear C4d in ptc (2-3 by IF or >0 by IHC), mod microvascular infl (G+ptc= 2+), endothelial injury by ↑ gene transcripts expr. in Bx.

Serologic evidence of DSA (HLA or otherwise)

All 3= ABMR, 1+ 2or3 = suspicious

C4d staining without evidence of rejection

Banff classification

Category 1: Normal biopsy or nonspecific changes

Category 2: Antibody-mediated changes Category 3: Borderline changes Category 4: TCMR Category 5: Interstitial fibrosis and tubular

atrophy Category 6: Other changes not considered to

be caused by acute or chronic rejection

Others; not acute or chronic rejection

BK virus nephropathy Posttransplant lymphoproliferative disorders Calcineurin inhibitor nephrotoxicity Acute tubular injury Recurrent disease De novo glomerulopathy (other than transplant

glomerulopathy) Pyelonephritis Drug-induced interstitial nephritis

CNI toxicity

Isometric vacuolization of proximal tubular cells Striped pattern of tubular atrophy/interstitial fibrosis Tubular microcalcinosis Arteriopathy with hyalinosis, vacuolization of

smooth muscle cells of arterioles Glomerulosclerosis, ischemic shrinkage of

glomeruli

Three final words ….

Fine Needle biopsy

Analysis of immunologically activated cells in grafts TCMR

Less invasive & repeatable Limitations in interpretation

Urine: the fluid biopsy of the kidney(Prof. Ramzi El Baroudi)

Yet pathology is never alone ….

•Assess patient carefully

•Need for pathology

•Do it early

•Do it properly

•Do it completely

•Interpret the whole picture

•Do it with care

Further references

Weening JJ, Jennette JC. Historical milestones in renal pathology. Virchows Arch. 2012;461(1):3-11. doi: 10.1007/s00428-012-1254-7.

Agarwal SK, Sethi S, Dinda AK. Basics of kidney biopsy: A nephrologist's perspective. Indian J Nephrol. 2013;23(4):243-52.

Stephen M.Bonsib. Atlas of medical renal pathology. Springer 2013

Agnes Fogo. Renal pathology. Avner E, Harmon W, Niaudet P, Yoshikawa N (eds). Pediatric nephrology. Springer 2009 (6th ed) 24:565-98

1. Pathological lesions denoting chronicity include

A cellular crescentsB vasculitis C tubular injuryD interstitial fibrosis

2. In acute antibody-mediated graft rejection, immunofluorescence shows deposits of

A IgAB C1q C C4dD Collagen type IVa

3. The picture shows

A Minimal change diseaseB Crescenteric nephritisC Focal segmental glomerulosclerosisD Diffuse mesangial sclerosis