Nephroblastomatosis

Key points

• Persistent metanephric blastema (beyond GA 36 wks) = nephrogenic rest
• Nephroblastomatosis = premalignant; carries increased risk of developing Wilms tumour, often bilateral/multifocal.
• Mostly seen in infancy (may not be detectable on initial imaging study); many lesions regress over time, but some persist or progress.
• May develop into Wilms tumour within the lesion ➞ need regular surveillance (often screening renal US at ~3 months until about 7-8 years; local protocol dependent)

Type

• Perilobar:
  • Peripheral cortex, subcapsular “rind” pattern.
  • Syndromes: Beckwith–Wiedemann, isolated hemihypertrophy, Perlman, trisomy 18.
• Intralobar:
  • Anywhere in parenchyma, patchy / nodular.
  • Higher Wilms risk.
  • Syndromes: Denys–Drash, WAGR, sporadic aniridia.

Imaging

Key imaging features

Typically appear as cortical, subcapsular, homogeneous, hypoenhancing tissue forming a rind or multiple small nodules; can be diffuse or multifocal.

Differentiating features from Wilms tumour

• In one series, a lesion size <1.75 cm had very high NPV (≈100%) and ~80% PPV for being a rest rather than Wilms – useful as a rough rule, but not absolute.
• Wilms tumour is usually spherical in shape & more likely to be exophytic.
  • Nephrogenic rests: more flat/rind-like, cortical, intraparenchymal.
  • Wilms: larger, lobulated, mass effect, distortion/exophytic.

Imaging findings suggesting conversion to Wilms tumour

• Rapid ↑ in size
• Stable or ↑ size while on chemotherapy (should shrink if it’s just rest under chemo)
• Nodule within initial lesions
• New heterogeneous appearance of mass