[Ultrastructural modifications of the tunica muscularis in congenital obstruction of the upper urinary tract. Physiopathological interpretations and anatomo-clinical correlations].

Upper excretory pathway musculature was studied by electron microscopy, both at the level of the obstruction and proximally. Two types of lesion were investigated: pyelo-ureteral junction anomalies and primary obstructive mega-ureter. Two types of muscle cell are recognized in the excretory pathway walls, typical and atypical cells, the latter being considered as possessing pace-maker activity and constituting almost total population of muscles of calices and pelvis. However, they were few in number in the pyelo-ureteral region and were practically absent from the ureter. Various conclusions can be drawn from the findings in this study. Both typical and atypical cells are modified in the obstructed upper excretory pathways. Ultrastructural appearances of lesions are identical at the site of an proximal to the obstruction. Modifications in these cells were: a rich sarcoplasmic reticulum, an increase in number of mitochondria and glycogen particles, disorganized distribution of contractile or cytoskeletal filaments, altered contact zones between contiguous smooth muscle cells, increased richness of granular endoplasmic reticulum and excessive development of the Golgi apparatus. More chronic lesions show enhanced fibrosis with reduced muscle contractility, the fibrosis affecting mainly elastic fibers in young patients and collagen fibers in more elderly subjects. The development of fibrosis may be due to changes in the granular endoplasmic reticulum and the Golgi apparatus. From the practical point of view, increase in fibrosis with duration of course of obstruction is an argument for as early as possible surgical intervention.