Wilms' tumour also called as nephroblastoma is a malignant renal neoplasm of childhood that arises from remnant of immature kidney that is from abnormal proliferation of metanephric blastema
without differentiation into glomeruli and tubules.
This is thought to result from the abnormal development and migration of the ureteric bud and metanephric blastema
during the fourth week to eighth week of gestation.
3,4) From a pathophysiology standpoint, horseshoe kidney occurs during the second and sixth week of gestation when the inferior portion of the metanephric blastema
fuses to form an isthmus, commonly in the lower renal pole (90%) and anteriorly to the aorta and vena cava.
The aetiology is unclear, although it is hypothesised that the problem lies with the ureteric bud crossing over to the contralateral metanephric blastema
, thereby inducing differentiation of a renal promordium.
These genes code for a variety of transcription and growth factors required for the regulation and orchestration of interactions between the ureteric bud and the metanephric blastema
and its predecessor's tissues, the mesonephric and pronephric ducts.
The ureteral bud arises from the dorsal aspect of the distal mesonephric duct, which extends in a dorsocranial fashion to meet and induce differentiation of the metanephric blastema
Over bending and rotation of the caudal end of the embryo prevents the ureteric bud from merging with the ipsilateral metanephric blastema
and thus is attracted towards the now more closer contralateral side.
Moreover, the ingrowth of the branching ureteric buds into the metanephric blastema
results in the characteristic lobulated appearance of the definitive kidney.
When the ureteric bud prematurely divides before penetrating the metanephric blastema
, this results in an incomplete duplex with ureters that meet before the bladder or a bifid renal pelvis.