Prevalence:

• 1 in 200,000 births.
• Mesoblastic nephroma (renal hamartoma) is the most frequent renal tumor, while Wilms’ tumor (nephroblastoma) is extremely rare.

Ultrasound diagnosis:

• In both tumors there is a solitary mass replacing the normal architecture of the whole or part of the kidney.
• Cystic areas may appear due to hemorrhagic necrosis.
• In most cases, there is associated polyhydramnios.

Associated abnormalities:

• The incidence of chromosomal abnormalities is not increased.
• Nephroblastoma can be associated with the Beckwith–Wiedemann syndrome with evidence of organomegaly and macroglossia.

Investigations:

• Detailed ultrasound examination.

Follow up:

• Ultrasound scans every 2-3 weeks to monitor the size of the tumor and development of heart failure and polyhydramnios.

Delivery:

• Place: hospital with facilities for neonatal intensive care. In about 20% of neonates there is hypertension due to overproduction of renin by the affected or normal kidney.
• Method: vaginal delivery.

Prognosis:

• Mesoblastic nephromas are benign, and nephrectomy is curative in the majority of cases. In a few cases there is local recurrence or distant metastases in the first year of life.
• Wilms’ tumor is malignant and about 50% are associated with genetic syndromes (such as Beckwith– Wiedemann syndrome). Treatment of the tumor requires nephrectomy, chemotherapy and sometimes radiotherapy; Survival is >90%.

Recurrence:

• Mesoblastic nephroma: no increased risk of recurrence.
• In nephroblastoma associated with Beckwith–Wiedemann syndrome (autosomal dominant) the risk is increased.