Congenital anomalies of the urinary tract are often found in multiple rather than single similar to congenital anomalies in the other systems. Among them it has been reported by many authors that the maldeveloped kidney are frequently associated with the congenital ureteral anomaly which causes obstruction. However, the etiology causing the maldeveloped kidney is still obscure and the morphological classification of this makes us confuse although the terms of hypoplasia, dysplasia, dysgenesis, aplasia and agenesis have been used. Except for hypoplasia and agenesis, these terms are used by different authors to mean different states.
From this point of view we reviewed and reevaluated the histological examinations of the kidneys to define the classification of the maldeveloped kidney: vesicoureteral reflux 4, ureteral stenosis 2, ureterovesical junction obstruction 1, ectopic ureter 13 and pyeloureteral junction obstruction 15. These renal specimens were obtained by biopsy or nephrectomy in the Urology Department of the Osaka University Hospital during the past 18 years.
The results were as follow. These 35 specimens were classified into 4 groups from the composition of glomeruli and tubules which were mature, primitive or absent.
Type I: Glomeruli and tubules are all of matured types although some hydronephrotic or inflammatory changes are observed. (12 cases)
Type II: Glomeruli and tubules are all of matured types with slight hydronephrosis or inflammation. However the kidney is definitely small. (4 cases)
Type III: Mixture of matured and primitive glomeruli and tubuli with moderately increased connective tissue. (16 cases)
Type IV: Only primitive tubules in severely increased connective tissue are observed without any glomerular component. (3 cases)
Therefore, the maldeveloped kidney should be classified into hypoplasia (type II), dysplasia (type III), dysgenesis (type IV) and agenesis.
Back pressure to the intrauterine kidney by disturbance of the urinary flow has been reported as one of the causes of the maldeveloped kidney. Also the time of onset of this is important. Relation of the classified types of the maldeveloped kidney to the time of onset of the congenital ureteral anomalies was discussed.