Multicystic Renal Dysplasia

Slide 1 · Multicystic renal dysplasia

Developmental pathology • gross and microscopic morphology • clinicopathologic interpretation

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning outcomes

Define multicystic renal dysplasia (MCDK) as a congenital maldevelopment rather than an acquired cystic disorder.

Identify the gross and histologic features that establish renal dysplasia.

Differentiate MCDK from polycystic disorders, hydronephrosis and cystic renal masses.

Explain how laterality and the contralateral kidney determine clinical consequences.

Distinguish the textbook surgical description from contemporary observation-based management.

Slide 3 · What the term describes

Congenital renal dysplasia with multiple cysts of variable size and disordered nephron/collecting-system development.

The affected organ is structurally abnormal, not simply a normal kidney bearing multiple cysts.

Unilateral or bilateral involvement is possible.

Slide 4 · Dysplasia is a developmental diagnosis

Developmental dysplasia

Acquired cyst formation

Abnormal organization arising during organogenesis

Cysts arise in previously formed kidney tissue

Primitive ducts and undifferentiated stroma may persist

Primitive dysplastic tissue is not the defining feature

Frequently associated with urinary-tract malformations

Context depends on the acquired process

Slide 5 · Why “multicystic” is only part of the name

The cysts are conspicuous grossly and on ultrasound.

The underlying disorder is abnormal renal differentiation and architectural organization.

Primitive ducts, mesenchymal cuffs and sometimes cartilage give histologic specificity.

Multiple cysts alone do not establish developmental dysplasia.

Slide 6 · Renal dysplasia has a spectrum

Abnormal kidney development

Dysplastic parenchyma

Cystic or noncystic phenotype

Multicystic renal dysplasia

Conceptual sequence — original editable schematic

Slide 7 · Affected tissue is not a normal functioning kidney

Cysts displace or replace much of the functioning parenchyma in the classic phenotype.

Some normal nephrons can still be identified microscopically.

An affected MCDK often contributes little or no useful overall renal function.

Clinical renal reserve depends on the functioning tissue elsewhere, especially in the opposite kidney.

Slide 8 · Developmental context: Two interacting components

Reciprocal developmental signaling

Ureteric bud

Metanephric mesenchyme

Collecting system

Nephron progenitors

Original developmental schematic

Slide 9 · Reciprocal induction builds the kidney

Ureteric bud enters mesenchyme

Branching of collecting system

Nephron induction and differentiation

Organized cortex–medulla–pelvis

Conceptual sequence — original editable schematic

Slide 10 · What normal renal architecture requires

Component

Normal result

Dysplastic contrast

Nephron differentiation

Mature tubules and glomeruli

Immature or aberrant structures may persist

Collecting-duct formation

Branching, organized drainage

Primitive ducts may be disordered

Stromal maturation

Ordered supportive interstitium

Persistent primitive mesenchyme

Renal organization

Recognizable parenchyma and pelvis

Architectural disorganization

Slide 11 · A developmental route to dysplasia

Impaired branching / differentiation

Disorganized ducts and nephron formation

Primitive stroma + variably sized cysts

Abnormal renal architecture

Conceptual sequence — original editable schematic

Slide 12 · Obstruction and dysplasia frequently coexist

Many cases with ureteropelvic obstruction, ureteral agenesis or ureteral atresia.

Other lower urinary tract anomalies may accompany the dysplastic kidney.

The association is important in a congenital anomalies of the kidney and urinary tract (CAKUT) evaluation.

An associated obstructive lesion does not establish the same sequence of causation in every case.

Slide 13 · The ureter is part of the pathology story

Kidney: Cystic disorganization

Ureteropelvic region

Ureter: Absent / atretic / obstructed

Slide 14 · Sporadic cases and genetic heterogeneity

Renal dysplasia as typically sporadic.

Genetic syndromes and inherited susceptibility can nevertheless occur, as described by NIDDK and developmental reviews.

Do not equate an isolated sporadic presentation with an invariably nongenetic disorder.

Look for additional anomalies before assuming an isolated renal phenotype.

Slide 15 · Why the CAKUT framework matters

Kidney morphology

Ureter and pelvis

Bladder / outlet

Contralateral kidney

Slide 16 · Laterality defines the principal clinical split

Unilateral MCDK

Bilateral MCDK

One dysplastic kidney

Both kidneys dysplastic

Contralateral kidney may maintain adequate function

Overall renal function is severely compromised

Usually favorable when the other kidney is healthy

Renal failure and serious neonatal consequences

Investigate additional urinary-tract anomalies

Requires specialist perinatal / renal planning

Slide 17 · Gross morphology: Extremely irregular outline

Original anatomical schematic

Irregular renal contour

Lobulated multicystic surface

Distorted parenchymal outline

Slide 18 · Gross morphology: Varied cyst diameters

Original anatomical schematic

Small cysts

Intermediate cysts

Large cysts

Slide 19 · Gross appearance reflects lost organization

The kidney is commonly enlarged and grossly distorted.

Cysts of unequal diameter interrupt normal architecture.

The cut surface does not resemble a simply dilated collecting system.

Gross morphology suggests dysplasia, but histology provides defining developmental evidence.

Slide 20 · Microscopic cyst lining

Cystic cavities can be lined by flattened epithelium.

The flattened lining is a nonspecific consequence of cystic dilatation.

Diagnostic confidence rises when epithelial cysts coexist with disorganized, immature renal tissue.

Slide 21 · Primitive ducts are central to histology

Primitive mesenchymal cuff

Immature duct epithelium

Central white space: Duct lumen

Schematic section—not an H&E specimen

Slide 22 · Undifferentiated mesenchyme is diagnostic context

Islands of undifferentiated mesenchyme among the cysts.

Primitive mesenchyme reflects incomplete renal tissue differentiation.

Cuffs surrounding immature ducts help distinguish dysplasia from ordinary cystic dilatation.

Read mesenchyme and ducts together, not as isolated findings.

Slide 23 · Cartilage signals aberrant differentiation

Immature duct / cyst

Focal cartilage island

Native schematic—not histology

Slide 24 · Cartilage is helpful—not required

Cartilage is a characteristic *possible* finding in renal dysplasia.

Its absence does not exclude the diagnosis.

Primitive ducts with mesenchymal collars and lobar disorganization are more reliable morphologic anchors.

Do not label focal cartilage itself as evidence of malignancy.

Slide 25 · Normal nephrons may persist within dysplasia

Residual normal structures

Dysplastic structures

Some formed glomeruli / nephrons may be present

Immature or poorly organized ducts

Function may be limited by overall abnormal organ

Large cysts disrupt parenchymal continuity

Finding a normal tubule does not negate dysplasia

Dysplasia is judged by the composite architecture

Slide 26 · Morphologic constellation—not a single clue

Irregular multicystic kidney

Flattened epithelial cyst lining

Primitive ducts + mesenchyme

Cartilage can be present

Slide 27 · Gross and microscopic findings reinforce each other

At gross examination

At microscopy

Uneven, enlarged multicystic kidney

Varied cyst sizes and epithelial linings

Distorted renal architecture

Lobar disorganization and immature ducts

Suspicion of a developmental anomaly

Primitive stroma and possible cartilage substantiate it

Slide 28 · Prenatal ultrasound often begins the work-up

Many cases are recognized before delivery during prenatal ultrasonography.

Assessment includes the cystic kidney, the opposite kidney and the urinary drainage system.

The amount of normal parenchyma and the pattern of cysts guide interpretation.

Postnatal ultrasound can confirm the suspected diagnosis.

Slide 29 · Imaging concept: Separate cysts versus dilated pelvis

Separate cystic spaces

Communicating dilated collecting system

Schematic—NOT diagnostic ultrasound

Slide 30 · Why cyst communication matters

MCDK pattern

Hydronephrotic pattern

Multiple cystic spaces, usually not communicating

Calyceal spaces often connect to renal pelvis

Disorganized architecture

Obstructed collecting-system dilation

May coexist with urinary-tract anomalies

Obstruction is itself the principal lesion

Slide 31 · Postnatal confirmation is contextual

Prenatal multicystic appearance

Postnatal renal + bladder ultrasound

Assess opposite kidney / urinary tract

Assign isolated vs complex phenotype

Conceptual sequence — original editable schematic

Slide 32 · Do not overlook the opposite kidney

It is the major determinant of renal reserve in unilateral MCDK.

Ultrasound assesses presence, structural integrity and compensatory growth.

Associated reflux or obstruction elsewhere can change follow-up needs.

The term “unilateral” does not automatically mean the urinary tract is otherwise normal.

Slide 33 · Unilateral MCDK: Mechanism of favorable prognosis

One kidney is dysplastic

Opposite kidney functions adequately

Renal homeostasis is maintained

Favorable outcome if no other lesions

Conceptual sequence — original editable schematic

Slide 34 · Bilateral disease: Why function fails

Dysplasia affects both kidneys

Little functional nephron reserve

Inadequate fetal / neonatal renal function

Severe outcome; Renal replacement may be needed

Conceptual sequence — original editable schematic

Slide 35 · Antenatal bilateral involvement raises different concerns

Both kidneys may lack sufficient functioning tissue.

Severe fetal renal impairment can affect amniotic-fluid production and pulmonary development.

Counseling must incorporate the entire fetal phenotype, not kidney appearance alone.

Perinatal/nephrology input is appropriate; Prognosis depends on functional severity.

Slide 36 · Spontaneous involution changes the longitudinal picture

Congenital multicystic kidney

Progressive involution may occur

Smaller residual tissue / absent visible lesion

Solitary functioning kidney phenotype

Conceptual sequence — original editable schematic

Slide 37 · Consequences of a single functioning kidney

Adequate early renal function does not make follow-up irrelevant.

Blood pressure, urine protein and kidney function may need periodic assessment.

The contralateral kidney should be evaluated for congenital anomalies.

An uncomplicated course is common, but monitoring is individualized.

Slide 38 · Differential: Autosomal recessive PKD

MCDK

Autosomal recessive PKD

Usually asymmetric / often unilateral

Usually bilateral, enlarged kidneys

Cysts uneven, multiple sizes

Small collecting-duct dilations in radial pattern

Primitive ducts + stroma / cartilage

Uniform cuboidal-lined collecting-duct cysts

Other urinary anomalies may accompany

Congenital hepatic fibrosis / bile duct lesions

Slide 39 · Differential: Autosomal dominant PKD

MCDK

Autosomal dominant PKD

Congenital dysplastic development

Inherited progressive cyst expansion

Variable cysts in disorganized kidney

Multiple tubule-derived cysts of varying linings

Frequently unilateral

Characteristically bilateral

Primitive immature tissue can be diagnostic

Polycystin gene abnormalities are characteristic

Slide 40 · Differential: Nephronophthisis

MCDK

Nephronophthisis

Often enlarged, irregular multicystic organ

Kidneys typically small, with corticomedullary cysts

Primitive ducts and mesenchymal islands

Tubular atrophy, basement-membrane changes, fibrosis

Congenital anomaly presentation

Progressive tubulointerstitial dysfunction in childhood

Ureteral malformations may coexist

Ciliopathy gene associations

Slide 41 · Differential: Medullary sponge kidney

MCDK

Medullary sponge kidney

Disorganized renal development

Collecting-duct cystic dilations limited to medulla

Grossly irregular / variable cyst sizes

Small cysts of papillary ducts

Functional tissue often markedly deficient

Renal function usually preserved

Primitive ducts and stroma

No defining primitive mesenchymal lesions

Slide 42 · Differential: Acquired and simple cysts

MCDK

Acquired / simple cystic disease

Present from abnormal development

Arises in established kidney

May replace kidney and disrupt architecture

Simple cysts often leave rest of kidney intact

Primitive ducts / stromal dysplasia

No obligatory immature stroma or cartilage

Often associated with urinary anomalies

Acquired disease often related to chronic dialysis

Slide 43 · A renal cystic mass is not automatically a tumor

An enlarged irregular multicystic kidney can be mistaken for a neoplasm.

The clinical differential includes congenital cystic lesions and less commonly cystic tumors.

Imaging evaluation of solid elements, architecture and age matters.

Uncertain atypical findings warrant expert evaluation, not a reflex assumption of benignity.

Slide 44 · The comparative diagnostic matrix

Entity

Core distribution

Decisive clue

MCDK

Often unilateral; Variable-sized cysts

Primitive ducts + stroma

ARPKD

Bilateral small collecting-duct cysts

Hepatic fibrotic/biliary lesions

ADPKD

Bilateral progressive cysts

Familial / polycystin association

Nephronophthisis

Corticomedullary cysts

Tubular atrophy + interstitial fibrosis

Hydronephrosis

Collecting-system dilation

Connected pelvis and calyces

Slide 45 · Triage a cystic fetal kidney systematically

Count the involved kidneys

Assess cyst size and communication

Look for collecting-system continuity

Inspect ureter / bladder / opposite kidney

Correlate anatomy with function

Slide 46 · A pathology specimen: What to document

Kidney size and contour; Number and heterogeneity of cysts.

Whether a recognizable pelvis and ureter are present.

Degree of renal parenchymal disorganization.

Primitive ducts and cuffs of undifferentiated mesenchyme.

Cartilage or other differentiation; Residual mature renal elements.

Slide 47 · Histologic pitfall: Cartilage is not obligatory

Unsound conclusion

Better interpretation

No cartilage → not dysplasia

Assess ducts, stroma, architecture and cysts

A cyst proves dysplasia

Cystic change alone is nonspecific

Normal nephrons exclude dysplasia

Residual normal tissue may coexist

“Dysplasia” means premalignant change

Here it means aberrant organogenesis

Slide 48 · A modern management distinction is essential

Robbins discussion

Contemporary pediatric approach

Unilateral cases may undergo nephrectomy

Observation is common when diagnosis is secure and asymptomatic

Focuses on excellent post-nephrectomy prognosis

Focuses on opposite kidney, involution and renal reserve

Historical clinical morphology framing

Surgery reserved for selected clinical problems

Slide 49 · Conservative care when unilateral and uncomplicated

Confirm that the multicystic lesion is typical and the other kidney is healthy.

Observation is generally favored over automatic nephrectomy.

Monitor for issues related to a solitary functioning kidney.

Specific imaging and clinic schedules depend on local pediatric nephrology/urology protocols.

Slide 50 · When does surgery enter consideration?

NIDDK notes nephrectomy may be considered for a persistently problematic nonfunctioning kidney.

Examples include troublesome infection, symptoms, or hypertension attributable to the abnormal kidney.

Suspicion of another diagnosis may require further assessment.

Size or absence of involution alone does not universally mandate removal.

Slide 51 · “Simple” versus “complex” MCDK

Simple unilateral phenotype

Complex phenotype

Typical MCDK and unaffected opposite kidney

Associated urinary/renal abnormalities

Compensatory contralateral growth

Potential impairment of renal reserve

May leave specialist urologic follow-up after confirmation

Requires individualized urology/nephrology follow-up

Slide 52 · Follow-up targets: Function, not just cyst size

Blood pressure

Urine protein

Renal function

Healthy kidney growth

Slide 53 · Management is a phenotype-driven decision

Secure MCDK diagnosis

Evaluate opposite kidney and urinary tract

Isolated + asymptomatic?

Observe; Intervene for complications

Conceptual sequence — original editable schematic

Slide 54 · Case 1: Antenatal cystic kidney

A routine fetal scan detects one irregular kidney containing numerous cysts of different sizes. The other kidney appears structurally normal.

Discussion questions

What developmental diagnosis is most likely?

What additional urinary-tract features should be assessed?

Which finding would most strongly alter predicted renal function?

Slide 55 · Case 1: Diagnostic reasoning

Working diagnosis: Unilateral multicystic renal dysplasia.

Cyst heterogeneity and loss of organized renal architecture support it.

Check collecting-system continuity, ureter/bladder and contralateral kidney.

Final risk assessment depends on preserved functional renal tissue in the opposite kidney.

Slide 56 · Case 2: A surgical pathology specimen

An irregular nephrectomy specimen shows large and small cysts. Sections reveal flattened cyst epithelium and immature ducts surrounded by primitive stroma.

Discussion questions

Which microscopic findings identify a developmental process?

Does absence of cartilage invalidate the diagnosis?

Why might the gross specimen mimic a cystic mass?

Slide 57 · Case 2: Morphologic diagnosis

Multicystic renal dysplasia: Epithelial cysts plus immature, disorganized ducts and mesenchymal cuffs.

Cartilage is supportive but not obligatory.

The lobulated multicystic gross mass explains potential confusion with neoplasia.

Describe associated abnormalities of the ureter and remaining renal tissue.

Slide 58 · Case 3: Bilateral cystic enlargement

A neonate has bilateral markedly abnormal kidneys. Both lack organized functioning parenchyma on evaluation.

Discussion questions

Why is prognosis unlike isolated unilateral MCDK?

How should bilateral involvement influence consultation?

Which differential with bilateral collecting-duct dilatation is important?

Slide 59 · Case 3: Function and differential

Bilateral disease can leave inadequate functioning nephron mass and cause renal failure.

Urgent multidisciplinary assessment is appropriate.

ARPKD is a key alternative: Bilateral small ductal dilatations and associated hepatic lesions.

Do not diagnose a specific entity from “bilateral cysts” alone.

Slide 60 · Three diagnostic anchors

Developmental disorganization

Primitive ducts + mesenchyme

Cysts of varying size

Evaluate the other kidney

Slide 61 · Four clinically actionable principles

Gross cysts are conspicuous; Histologic dysplasia is the defining process.

Unilateral and bilateral involvement have profoundly different functional implications.

Assess the entire urinary tract, not the affected kidney in isolation.

For typical uncomplicated unilateral MCDK, modern care commonly observes rather than removes the lesion.

Slide 62 · References and source distinctions

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th ed. 2026; Chapter 20, p. 859 (primary morphologic source).

Jain S, Chen F. Developmental pathology of congenital kidney and urinary tract anomalies. Clin Kidney J. 2019;12:382–399.

NIDDK. Multicystic Dysplastic Kidney. Updated January 2023.

Psooy K. MCDK in the neonate: The role of the urologist. Can Urol Assoc J. 2016.

UC Davis Department of Pathology. Renal dysplasia case discussion. January 2022.