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