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

Purpose: To study the anatomy of the normal ureteropelvic junction (UPJ) an d investigate its pressure response to distension, aiming at elucidation of its function in the light of its anatomical structure. Method: 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 m icroscopically after staining with hematoxylin and eosin and Masson's trich rome. Furthermore, the length of the UPJ as well as the UPJ pressure respon se 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 r eported 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. Results: Grossly, there were no features characteristic of the UPJ external ly, 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 s tructured muscle fiber arrangement were lacking in the adjacent renal pelvi c and ureteral walls. The mean UPJ length in adults as measured manometrica lly 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 UP J locally anesthetized by injecting xylocaine into its tissue, but there wa s response when saline was injected into the tissue of the UPJ.. Conclusion : The UPJ might be identifiable by the presence of the mucosal rosette. The reaction of the UPJ to distension probably indicates that the UPJ possesse s a motile activity. This, as well as the presence of a structured muscle c oat at the UPJ would suggest the presence of a 'sphincter' at the UPJ.