Ureteral structure and ultrastructure. Part III. The congenitally dilated ureter (megaureter)

Abstract

The short descriptive term megaureter, applied aptly to the ureter(s) that are out of proportion to the rest of the urinary tract, has been applied more loosely to a variety of congenitally and massively dilated ureters to the extent that it has become non specific in meaning. In this study a classification is proposed for differentiating clearly the types of megaureter. These types, excluding the primary obstructive types, are defined by ultrastructural study, and are the ureter with reflux; the obstructive ureter (primary and secondary); the dysplastic ureter; and the prune belly syndrome. In a selected group of 16 congenitally dilated ureters the light and electron microscopic findings were compared to the clinicoradiologic features of each ureter. These dilated ureters exhibit qualitative and/or quantitative muscular deficiencies. The obstructed megaureters secondary to posterior urethral valves and the megaureters with reflux show non specific pathologic changes in response to increased work load or decompensation but infection within the ureter is detrimental to the muscle cells. The ureters in babies with prune belly syndrome suffer from reduced muscle cell population and a distinct myopathy involving the myofilaments within the muscle cells. The dysplastic ureter is morphologically an end stage ureter wherein the muscle cells are severely compromised. Whether this is an underdevelopment or exhaustion from repeated infections is a matter for speculation.