Ureteropelvic junction: A study of its anatomical structure and function. Ureteropelvic junction sphincter?

To study the anatomy of the normal ureteropelvic junction (UPJ) and investigate its pressure response to distension, aiming at elucidation of its function in the light of its anatomical structure.

The UPJ of 25 cadaveric specimens (15 male, 10 female; 15 adults, mean age 33.6 +/- 8.4 years; 10 fully mature neonatal deaths) was studied morphologically and microscopically after staining with hematoxylin and eosin and Masson's trichrome. Furthermore, the length of the UPJ as well as the UPJ pressure response to UPJ distension were assessed in 13 subjects (8 men, 5 women, age 48.8 +/- 10.3 years). The response of the anesthetized UPJ to distension was reported in 7/13 subjects and of the saline-injected UPJ in the remaining 6/13. The UPJ had been anesthetized by injecting 1% xylocaine into its wall.

Grossly, there were no features characteristic of the UPJ externally, although internally the mucosa was thrown into folds forming a 'mucosal rosette'. Microscopic examination showed the muscle fibers to be arranged in two well-formed layers: circular and longitudinal. Mucosal folding and structured muscle fiber arrangement were lacking in the adjacent renal pelvic and ureteral walls. The mean UPJ length in adults as measured manometrically by the pull-through technique was 6.9 +/- 1.5 mm. UPJ distension led to an elevated UPJ pressure; the latter increased with increase of the volume of distension. There was no UPJ pressure response to distension of the UPJ locally anesthetized by injecting xylocaine into its tissue, but there was response when saline was injected into the tissue of the UPJ.

The UPJ might be identifiable by the presence of the mucosal rosette. The reaction of the UPJ to distension probably indicates that the UPJ possesses a motile activity. This, as well as the presence of a structured muscle coat at the UPJ would suggest the presence of a 'sphincter' at the UPJ.