Tamm-Horsfall protein: unusual, large perinephric deposits

A case in which unusually large deposits of Tamm-Horsfall protein were identified in perinephric adipose tissue is presented. The deposition around the kidney in this case was most likely due to calyceal rupture, secondary to distal ureteric obstruction. The peculiar gross and microscopic appearance of these deposits, their intense staining with the periodic acid--Schiff technique, and their association microscopically with epithelial fragments raised the possibility of infiltration by mucin-producing adenocarcinoma. The localization of Tamm-Horsfall protein in the deposits by the immunoperoxidase technique helped to confirm their true nature.