RENAL DYSPLASIA

Abstract

The human kidney is the most advanced in phylogeny and its embryonic development through three distinct organ systems reflects the stages of evolution of the organ through phylogeny. The primitive kidneys, the pronephros and mesonephros, become vestigial in the human being but act as inducers of the definitive metanephric kidney.
Maldeveloped kidneys which are frequently associated with congenital ureteral and/or lower urinary tract abnormalities have usually been devided into agenesis, aplasia and hypoplasia. Recently, the term renal dysplasia is used by many authors to mean renal maldevelopment, but its definition, etiology and classification are still controvertial.
In this paper, renal dysplasia means congenital underdevelopment or developmental arrest of the renal parenchyma, i. e. the persistence of fetal structures “primitive ducts”. Other so-called ‘dysplastic’ structures, i. e. metaplastic cartilage, primitive glomeruli, etc, should be defined as dysplastic only when these structures were found with the primitive ducts.
The clinical and pathological findings in 120 patients submitted to partial or total nephrectomy and 15 autopsied specimens from the neonates and the immature babies have been reviewed. Histological examination of these kidneys showed the evidence of dysplasia in 24 in association with various abnormalities of the urinary tract (ectopic ureter 9, ureterocele 5, refluxing megaloureter 3, congenital hydronephrosis 2, multicystic kidney 3, distal ureteral atresia 2).
There were 10 duplex systems in which upper half kidneys were involved in 9, lower half kidney in 1 (VUR).
Renal dysplasia should be understood not only as a part of maldeveloped kidney, but also as a part of cystic disorders of kidney, the correlation of which were summarized in Table 3.
From the clinical view of renal pathology and urinary tract abnormalities, renal dysplasia was classified into three groups. In group 1, total dysplasia (aplastic, multicystic) was associated with atresia or absence of the renal pelvis and ureter. In group 2, hypoplastic dysplasia or dysplasia of the upper or lower half kidney; the ureter, although patent, had some anatomical or functional abnormalities which resulted in urinary stasis and reflux. In group 3, hydronephrotic dysplasia with multiple cortical cysts, was associated mostly with obstruction of lower urinary tract and infrequently with congenital hydronephrosis. There are sometimes difficulties to strictly classify and differenciate these 3 groups because of existence of intermediate one.
Back pressure from the urinary stasis or reflux in the fetal period may be one of the most important factors in the development of the dysplastic kidney, and the importance of the onset of injuries to the developing fetal kidney was stressed.