The seminal vesicle is a normal anatomical structure at the base (upper end) of the prostate. It is sometimes sampled by prostate biopsies aimed at the base. Seminal vesicle biopsies are usually short with a thick smooth muscle layer and a mucosa with crowded small glands.
The seminal vesicle mucosa may mimick prostate cancer because the glands sometimes have a pronounced nuclear atypia. This atypia is not malignant and looks degenerative. The nuclei are large with dense, dark chromatin. The nuclear atypia is often too severe for a prostate cancer, with well-developed glandular architecture and the very dense chromatin is not typical for prostate cancer. The glands may contain sticky secretions (chewing-gum like) and the epithelium may contain yellow pigment.