bilaterally enlarged kidneys + increased echogenicity + poor/absent CMD + no pelvicalyceal dilatation/obstruction + normal AFI
| Feature | Renal Dysplasia | Nephronophthisis | ARPKD | ADPKD | MCDK |
|---|---|---|---|---|---|
| Laterality | Uni- or bilateral | Usually bilateral | Bilateral | Usually bilateral | Uni- or bilateral |
| Kidney size | Variable: small, normal or enlarged | Infantile NPHP: enlarged; juvenile form usually normal/small | Markedly enlarged | Usually enlarged | Variable, often enlarged initially |
| Echogenicity | ↑ diffuse | ↑ diffuse | Markedly ↑ | ↑, often variable | ↑ echogenic stroma |
| CMD | Reduced/absent | Often reduced | Usually reduced/absent | Variable; may be relatively preserved early | Absent normal architecture |
| Cysts | May be absent; if present, variable size | Microcysts, classically corticomedullary | Numerous tiny cysts, often not individually visible | Macrocysts may be seen later, often variable | Multiple macroscopic noncommunicating cysts |
| Renal pelvis | Usually not dilated | Usually not dilated | Usually not dilated | Usually not dilated | No communicating collecting system |
| AFI | Normal if unilateral | Usually normal early; oligohydramnios with severe bilateral disease | Often ↓ later/severe | Usually normal | Normal if unilateral |
| Extrarenal clues | CAKUT, genital, cardiac etc. | Ciliopathy: CNS/eye/liver/skeletal findings depending on gene | Congenital hepatic fibrosis | Liver cysts/family history, usually postnatal | Usually urinary tract/contralateral anomalies |
The cyst pattern is extremely useful
Think of the location and size rather than simply "cysts present/absent."
Dysplasia/MCDK
→ irregular cysts of variable size
→ obvious structural disorganization
→ in MCDK, multiple noncommunicating macrocysts replace the parenchyma.
Nephronophthisis
→ very small microcysts, often at/near the corticomedullary junction
→ may be completely invisible prenatally.
ARPKD
→ innumerable microscopic collecting-duct cysts
→ produces a very uniform, diffusely echogenic enlarged kidney, rather than a few discrete large cysts.
ADPKD
→ cysts tend to be larger and more variable
→ prenatal appearance is quite variable and may simply be bilateral enlarged echogenic kidneys.
Nephronophthisis (NPHP) in detail
Nephronophthisis is an autosomal-recessive tubulointerstitial kidney disease and a ciliopathy. The basic defect is abnormal primary-cilium function in tubular epithelial cells, leading over time to tubular injury, interstitial fibrosis, and progressive loss of renal function. It is not primarily a glomerular disease.
Juvenile NPHP
This is the classic and most common form.
Typical presentation:
• Polyuria and polydipsia from impaired concentrating ability
• Growth retardation
• Chronic anemia
• Progressive CKD
• ESRD usually in childhood/adolescence, although age varies considerably
Ultrasound later in childhood:
• Normal or small kidneys
• Increased echogenicity
• Poor CMD
• Eventually corticomedullary cysts
Infantile NPHP
This is particularly relevant to your fetus.
It is usually caused by variants in genes such as NPHP2/INVS, NPHP3, NPHP6/CEP290, TMEM67, NEK8, RPGRIP1L, WDR19, IFT172, among others.
The phenotype is much more severe.
Prenatally it can produce:
bilaterally enlarged kidneys + increased echogenicity + poor CMD
and, in severe cases:
oligohydramnios → pulmonary hypoplasia ± limb contractures/facial abnormalities.
Histologically, NPHP is primarily a tubulointerstitial disease.
There is:
• Tubular epithelial injury
• Tubular basement membrane abnormalities
• Tubular dilatation/cyst formation
• Interstitial fibrosis
• Progressive nephron loss
The cysts tend to develop at the corticomedullary region, although they are not necessarily visible on fetal imaging.
extrarenal abnormalities
CNS
• Vermian hypoplasia
• Molar tooth configuration/Joubert spectrum
• Ventriculomegaly
• Other CNS malformations
Eyes
• Microphthalmia
• Coloboma
• Retinal disease cannot usually be assessed directly prenatally, but severe syndromic phenotypes may have structural ocular abnormalities.
Skeletal
• Polydactyly
• Narrow thorax
• Short limbs
• Brachydactyly
Liver
• Hepatomegaly
• Abnormal liver echotexture
• Later evidence of congenital hepatic fibrosis is much more difficult to establish prenatally.
Cardiac
• Congenital heart disease in some genotypes
Situs
• Situs inversus/heterotaxy, especially with INVS/NPHP3-related disease.
Genital
• Abnormal genital development can occur in some NPHP-related ciliopathies.