STEPTRACKERRENAL | PATHOLOGY + EMBRYOLOGY + GENETICS | HIGH-YIELD REVIEW

Congenital & Cystic Kidney Disease

Kidneys that never form, fuse, obstruct or fill with cysts — and the genetic cystic diseases that bring extra-renal clues.

FOCUS ON
No fetal urine → oligohydramnios → Potter sequence (pulmonary hypoplasia, flat face, limb deformities). Horseshoe kidney is caught under the IMA. ADPKD (PKD1/PKD2): adults, huge bilateral cystic kidneys, hypertension, berry aneurysms, liver cysts, MVP. ARPKD: infants, Potter sequence, congenital hepatic fibrosis.
DISORDER
MECHANISM · GENETICS
FEATURES
CLUE
Bilateral renal agenesis
Ureteric bud fails to develop → no metanephric induction
Oligohydramnios → Potter sequence; incompatible with life
Pulmonary hypoplasia is the cause of death
Unilateral renal agenesis
One ureteric bud absent
Often incidental; compensatory hypertrophy of the other kidney
Associated genital tract anomalies
Horseshoe kidney
Inferior poles fuse; ascent blocked by the inferior mesenteric artery
Low-lying kidneys; usually normal function; hydronephrosis, stones, infection
Turner syndrome, trisomies 13/18/21 · ↑ Wilms
Multicystic dysplastic kidney
Abnormal ureteric bud–mesenchyme interaction → nonfunctional cysts + cartilage
Unilateral flank mass in a newborn; other kidney compensates
Bilateral → Potter sequence
Ureteropelvic junction obstruction
Incomplete recanalization / abnormal peristalsis at the UPJ (last part to canalize)
Most common cause of hydronephrosis in infants
Prenatal ultrasound finding
Posterior urethral valves
Membrane in the posterior urethra of males
Bladder outlet obstruction → bilateral hydronephrosis, distended bladder, oligohydramnios
Most common cause of urinary obstruction in male newborns
ADPKD
PKD1 (chr 16, polycystin-1, ~85%) or PKD2 (chr 4); cysts from all nephron segments
Adults: bilateral enlarged cystic kidneys, flank pain, hematuria, hypertension (↑ renin), stones, UTIs → CKD
Tolvaptan (V2 antagonist) slows growth
ADPKD — extrarenal
Polycystin defect in other tissues
Berry aneurysms (SAH), hepatic cysts, mitral valve prolapse, colonic diverticula
Sudden severe headache in ADPKD
ARPKD
PKHD1 (fibrocystin), autosomal recessive; collecting duct cysts
Infants: enlarged spongy kidneys, Potter sequence, hypertension, renal failure
Congenital hepatic fibrosis → portal hypertension
ADTKD (medullary cystic kidney disease)
Autosomal dominant (UMOD and others); tubulointerstitial fibrosis
Small, shrunken kidneys; cysts at the corticomedullary junction; poor concentrating ability
Hyperuricemia, gout; progresses to ESRD
Medullary sponge kidney
Dilated medullary collecting ducts
Usually benign; nephrocalcinosis, calcium stones, UTIs
"Paintbrush" pattern on urography
Simple & acquired cysts
Simple: common with age · acquired: long-term dialysis
Simple: smooth, fluid-filled, benign · acquired: multiple cysts
Dialysis cysts → ↑ renal cell carcinoma

Mechanism — building and losing a kidney

Ureteric budFrom mesonephric duct
→
Collecting systemUreter, pelvis, calyces, collecting ducts
Metanephric mesenchyme
→
NephronGlomerulus → DCT
No fetal urineAgenesis, ARPKD, PUV
→
Oligohydramnios
→
Potter sequenceLung hypoplasia, flat face, clubfeet

ADPKD vs ARPKD

FEATURE
ADPKD
ARPKD
Gene
PKD1 (16), PKD2 (4)
PKHD1 (6)
Age
Adults
Infants
Cysts
All nephron segments, large
Collecting ducts, small radial
Liver
Hepatic cysts
Congenital hepatic fibrosis
Vessels / heart
Berry aneurysms, MVP
Hypertension
Neonatal
Usually none
Potter sequence

How it's tested

COMMON CONFUSIONADPKD gives big kidneys; ADTKD (medullary cystic disease) gives small, shrunken kidneys with poor concentrating ability.
THE TRAPAn ADPKD patient with "the worst headache of my life" has a ruptured berry aneurysm until proven otherwise — not a migraine.
YOUR APPROACHAge (fetus, infant, adult) → amniotic fluid → kidney size and cyst pattern → inheritance → extra-renal organ (brain, liver, heart).

If you see… think…

Oligohydramnios, flat face, clubfeet, lung hypoplasia → Potter sequence
Kidneys fused at lower poles, trapped below the IMA → horseshoe kidney
Newborn boy with distended bladder and bilateral hydronephrosis → posterior urethral valves
Most common cause of hydronephrosis in an infant → UPJ obstruction
Adult with hematuria, hypertension, big bumpy kidneys → ADPKD
ADPKD with sudden thunderclap headache → ruptured berry aneurysm
Infant with enlarged kidneys and portal hypertension → ARPKD
Small kidneys with corticomedullary cysts, gout → ADTKD (medullary cystic)
Long-term dialysis patient with new renal mass → RCC in acquired cystic disease
Unilateral nonfunctional cystic kidney in a newborn → multicystic dysplastic kidney