Tubulovenous communication in myeloma kidney. Tubular prolapse and tubular transformation of renal vein.

We studied renal histopathologic findings of 20 autopsy cases with multiple myeloma with particular attention to structural tubulovenous relationship. Urinary deposition in renal vein or lymphatics, which has been previously noted in pyelonephritis, obstructive uropathy, or vesicoureteral reflux was found in 14 cases. Four of 14 cases had unique tubulovenous communications designated as tubular prolase and tubular transformation of vein. Such communications were most frequently seen at the architectural weak point where the thin-walled interlobar vein and their tributaries adjoin the renal pyramid. Simultaneously, Tamm-Horsfall protein used as a marker for the location of urine was detected in renal vein. These changes had no significant correlation to morphologic severity of myeloma kidney or clinical manifestations of renal failure. Thus, tubulovenous communication producing backflow of urine into the circulation is frequently observed among myeloma kidney as well as other tubulointerstitial nephritis, but its clinical significance is unclear.