The fine structure of human pseudomembranous trigonitis.

The present investigation provides a histological and fine structural description of pseudomembranous trigonitis, an ill-understood metaplastic condition affecting particularly the female trigone. Normal trigonal urothelium consists of 3 cell layers (basal, intermediate and superficial), whereas pseudomembranous trigonitis constitutes many layers of stratified squamous epithelium. The basal cells contain prominent nuclei with condensed chromatin, nucleoli and nuclear bodies. The cytoplasm of these cells is rich in mitochondria. The profiles of the urothelial cells become progressively elongated, their nuclei increasingly smaller and their content of cell organelles gradually reduced as the luminal surface is approached. The squamous surface cells, linked by desmosomes, retain many longitudinally arranged fine filaments, together with an occasional degenerate nucleus. The mitotic index of pseudomembranous trigonitis is 0.17% (SD 0.09%), i.e. significantly higher than normal (0%).