Unilateral echogenic kidney with polyhydramnios
Unilateral PUJO progressing to echogenic kidney with CMD loss and polyhydramnios usually reflects progressive obstructive dysplasia of the affected kidney with preserved global renal function due to a normal contralateral kidney.
Polyhydramnios suggests:
- normal or increased fetal urine output
- impaired swallowing
- GI obstruction
- Syndromic association
A. Multicystic dysplastic kidney (MCDK)
Very common cause of unilateral echogenic kidney.
Ultrasound:
- Multiple non-communicating cysts
- No normal renal parenchyma
- Enlarged kidney initially
Amniotic fluid: Usually normal
But polyhydramnios may occur if:
- contralateral kidney hyperfunctions
- associated anomalies present
B. Unilateral obstructive uropathy
- ureteropelvic junction obstruction
- megaureter
Can lead to:
- enlarged echogenic kidney
- hydronephrosis
Polyhydramnios may occur if:
- renal function preserved
- urine output increased
Congenital mesoblastic nephroma
Unilateral echogenic kidney + polyhydramnios
Mechanism of polyhydramnios:
Tumor produces:
- polyuria
OR
- hypercalcemia-related diuresis
Ultrasound:
- Solid renal mass
- Enlarged kidney
- Increased vascularity
Syndromic renal enlargement
Beckwith-Wiedemann syndrome
- enlarged echogenic kidney
- polyhydramnios
Associated with:
- macrosomia
- macroglossia
- omphalocele
Simpson-Golabi-Behmel syndrome
Also causes:
- renal enlargement
- polyhydramnios
- macrosomia
Renal cystic disease (unilateral presentation)
Autosomal dominant polycystic kidney disease
Usually bilateral but: early unilateral echogenic kidney possible
Fluid often:
- normal or increased
Renal vein thrombosis
Features:
- enlarged echogenic kidney
- altered Doppler
Kidney morphology
| Pattern | Likely cause |
|---|---|
| Multiple cysts | MCDK |
| Solid mass | Mesoblastic nephroma |
| Dilated pelvis | Obstruction |
Kidney size
Very large kidney: tumor or obstruction
Vascularity, High flow mass: mesoblastic nephroma
Findings
- Unilateral PUJO
- Kidney becoming echogenic
- Loss of CMD
- Polyhydramnios
- Contralateral kidney normal
Most likely contralateral compensatory hyperfiltration
Interpretation
This suggests: progressive dysplasia or parenchymal damage in the obstructed kidney
BUT
overall fetal renal function remains normal because the opposite kidney is compensating.
So the polyhydramnios is not due to renal failure, but due to preserved or increased urine output.
Ureteropelvic junction obstruction
Evolution pattern (classic)
Early:
- hydronephrosis
- preserved CMD
Later:
- renal parenchymal thinning
- increasing echogenicity
- loss of CMD
Final stage:
- dysplastic kidney
- reduced function
Why polyhydramnios occurs
Because:
- contralateral kidney is normal
- compensatory hyperfiltration
- increased urine production
This is well recognized in unilateral obstruction.
Mechanism of echogenic kidney with CMD loss
This reflects: chronic high-pressure damage
Pathology includes:
- tubular atrophy
- interstitial fibrosis
- cystic dysplasia
- nephron loss
Ultrasound correlate:
- increased echogenicity
- blurred corticomedullary junction
This is secondary renal dysplasia.
Red flags
- progressive parenchymal thinning
- increasing echogenicity
- severe hydronephrosis
- cortical cysts
These suggest: irreversible renal damage
PUJO → echogenic kidney + CMD loss + polyhydramnios
Most consistent with: progressive unilateral obstructive nephropathy with compensatory contralateral hyperfiltration