Pathways of urinary backflow in obstructive uropathy. Demonstration by pigmented gelatin injection and Tamm-Horsfall uromucoprotein markers.

The exact pathways of urinary reflux into the renal veins were studied in four cases of clinical obstructive uropathy and in 50 normal human cadaver kidneys. In the four clinical cases Tamm-Horsfall uromucoprotein was used as a marker for location of urine. Routine light microscopy and indirect immunofluorescence for Tamm-Horsfall uromucoprotein using rabbit antiserum showed tubular backflow up to the glomerulus. Dilated tubules filled with Tamm-Horsfall uromucoprotein ruptured into thin walled veins, forming tubulovenous anastomoses with extrusion of their contents into veins. The uromucoprotein was present in interlobar and arcuate veins with superimposed thrombosis and thrombophlebitis. Injection studies using pigmented gelatin in 45 normal cadaver kidneys and pigmented vinylite with corrosion casts in five additional kidneys complemented the clinical studies. Two types of urovascular communication were produced: the less frequent direct pyelovenous communication between a rupturing fornix and an adjacent small vein, and the more common indirect pyelovenous communication in which a ruptured fornix produced a sinus extravasate, which extended along the perivenous spaces of interlobar and arcuate veins. This extravasate gained access into the veins at points of rupture where venous tributaries joined the major veins in the renal medulla. The clinical implications of these tubulovenous and pyelovenous pathways of urinary reflux include backflow of whole urine and continued nephronic function in obstructive uropathy, "reverse backflow" of blood and hematuria, and a direct access for infectious agents into the circulation. These channels provide anatomic correlates for radiologic findings of extravasates and some backflow patterns of contrast material in pyelograms of clinical obstructive uropathy. The possible immunologic consequences of refluxing Tamm-Horsfall uromucoprotein gaining access to tissues and circulation are speculative.