A HISTOLOGICAL STUDY OF THE DILATED URETERS IN CHILDREN

Abstract

The pupose of this tudy is to classify the dilated ureters from histological stand point. Ninety-four ureters from 71 children, who showed moderate to severe dilatation of the urters in the urographic studies, were examined under a light microscope. The ureters were divided into 4 groups according to the findings of the muscle layers of the dilated portions as follows:
Group 1: normal muscle layers (42 ureters),
Group 2: hypertrophy and hyperplasia of the muscle bundles (30 urters). Most of the ureters in this group were accompanied with proliferation of interstitial connective tissues.
Group 3: hypoplasia of the muscle bundles (8 ureters). Muscle bundles were thin and muscle cells were also hypoplastic.
Group 4: aplasia of the muscle bundles (14 ureters), in which muscle bundles were not observed. Instead, there were scattered fragments of several atrophic muscle fibers within abundant connective tissues.
According to this classification, the histological features of the dilated ureters were compared with several disorders.
1) Vesico-ureteral reflux (45 ureters): thirty-six ureters (80%) were inclused in the group 1. Among the 8 ureters of the group 2, 7 were moderately to severely dilated on the intravenous pyelogram. One ureter of group 4 was associated with a dysplastic kidney.
2) Primary megaureter (12 ureters): nine ureters (75%) were in the group 2. There was a fairly good correlation between the grade of ureteral dilatation and muscular hypertrophy.
3) Ureterocele (12 ureters) and ectopic ureter (10 ureters): nine of the ureteroceles and 8 of the ectopic ureters showed the findings of either group 3 or group 4. Correlation of the position of the ureteral orifice and the ureteral musculature was investigated. If a ureter opens caudally, the muscle bundles tend to become hypoplastic or aplastic.
4) Prune belly syndrome (4 ureters): three ureters exhibited typical features of group 4. In one of them, the histological difference between the middle and the lower portion of the ureter was examined. In contrast to the previous reports, the muscle cells were proved to be more abundant in the lower portion.
5) Neurogenic bladder (6 ureters), posterior urethral valve (3 ureters): these dialted ureters secondary to the obstruction of the lower urinary tract were included in group 2. In general, the hypertropny of the muscle bundles and the increased amount of connective tissue in these disorders were more prominent than in the primary megaureter. Bacterial infection was remarkably observed in these ureters.
6) Twenty-six kidneys were examined histologically, and 17 were diagnosed as dysplastic. Fourteen ureters (82%) of the dysplastic kidneys had the muscle layers of either group 3 or group 4. This would suggest a coincidence of the abnormal structures of the ureteral muscles and the presence of renal dysplasia in these disorders.
7) Several different portions were examined and compared in 9 ureters. Like normal ureters, 5 of them, irrespective of their histological group, revealed an increase in thickenss and amount of the muscle bundles in the ureter near the ureterovesical junction. Another ureter showed the same histology of group 4 in either portions. In other two ureters, the middle portion was found to be aplastic whereas the upper and lower portions were hypoplastic but muscle bundles could be apparently observed. In one ureter, the muscle layer was normal in the middle portion but it was severely hypoplastic in the upper and lower portions. These observations on pathologic ureters were not described in previous reports.