ABSTRACT
Congenital mesoblastic nephroma (CMN) first described by
Kastner in 1921,1 is the most common renal tumor in the
neonate, although rare cases present in later childhood. It is
also known as a fetal renal hamartoma, mesenchymal
hamartoma of infancy, or lipomyomatous hamartoma. It has
an incidence of 2.8% of all renal tumors of childhood, with a
mean age of presentation of 3.4 months in contrast to an
average age of three years in Wilms’ tumors.2 It has been
documented as being 22.8% of all primary tumors in children
one year old or less.3 A neoplasm in the kidney of a child less
than three months old is usually a CMN. The majority of renal
neoplasms originating in the fetus and found during the first
weeks of life, differ in structure and in biological behavior
from a nephroblastoma. In contrast to cystic lesions of the
kidney, solid renal neoplasms are rare in the newborn and
account for only 8% of neonatal tumors. In the Children’s
Cancer Group (CCG) Neonatal Study, there were 25 neonatal
renal neoplasms, of which 17 were CMN and the rest were
Wilms’ tumors.4 A review of neonatal Wilms’ tumors in the
national Wilms’ tumor register identified 15 cases out of 6832
patients with an incidence of 0.16% demonstrating how rare
malignant renal neoplasms are in neonates. Although prenatal
ultrasound is capable of detecting renal neoplasms in utero,
there are no specific sonographic characteristics that can
differentiate a CMN from a Wilms’ tumor. Both tumors
present as a palpable abdominal mass in the neonate. Males
outnumber females by 2 to 1 with CMN and both sexes are
equally affected by Wilms’ tumors.
