Seminal vesicle calculus and hemospermia:

Seminal vesicle calculi are a known cause of passage of blood in semen. This patient had hemospermia. TRUS images show a calculus in right seminal vesicle. Possibly such calculi cause irritation and trauma to the delicate walls of the seminal vesicle resulting in hemorrhage. But surgery may be the final alternative in this case.
View more images of a similar case at:
http://www.ultrasound-images.com/prostate.htm