Muscle Dysplasia in Megaureters

We have previously reported the relevance of muscle dysplasia to the nonreflux megaureter. On electron microscopy, muscle cells which are scattered in large amounts of connective tissue without any bundle formation are found to be deficient in myosin filaments, which, with actin filaments, are believed to be an essential contractile unit of smooth muscle. Investigations of these dysplastic features of the ureter were extended to various other congenital disorders of the ureter experienced in our institution from 1963 to 1981. Muscle dysplasia was found in 8 of 34 cases of nonreflux megaureter, in 1 of 22 cases of reflux megaureter, in 4 of 23 cases of ectopic ureter of single system, in 4 of 9 cases of ectopic ureter of duplex system, 0 of 4 cases of the ureter of ureterocele of single system and in 1 of 13 cases of the ureter of ureterocele of duplex system. When muscle dysplasia was extensive, involving the whole length of the dilated ureter, incidence of associated renal dysmorphism was high in that 12 of 17 ureteral units as such demonstrated either severe renal dysplasia (9) or hypoplasia (3). Similar muscle dysplasia was also found in most of the dome of ureterocele (in 5 of 6 and 12 of 13 ureteroceles of single and duplex systems respectively). Muscle dysplasia is discussed as to its genesis, relevance to various congenital ureteral disorders and clinical implications.