In cases of acute prostatitis the prostate remains normal or increased in size with regular lobe symmetry. In the early stages of mild forms a hypoechogenic peri-urethral halo is visualized which is due tooedema. As the disease progresses hypoechogenic intra-glandular filaments are observed. Caused by inflammation-induced blood vessel dilation they are sometimes associated with dilation of the Santorini periprostatic vein plexus. In severe forms of acute prostatitis the prostate is enlarged and areas of hypoechogenic tissue are larger because the inflammation is more extended. In older patients or in patients with compromised immunological systems a prostatic abscess may develop. On the ultrasound screen the abscess appears as a transonic area with irregular edges