This case of urinary obstruction with short anamnesis illuminates the early tissue reaction to urine extravasation, especially the Tamm-Horsfall protein. The latter becomes organized in the manner of a foreign body substance and drains via ectatic renal lymph vessels and reopened lymphovenous shunts into the intrarenal venous system. Polypoid formations (thromboids) with or without vessel obliteration appear to result in a clinical course of severe renal impairment.