Prostate

Dr Craig Hacking ◉ and Dr Julian Maingard et al.

The prostate gland is part of the male reproductive system and is the largest male accessory gland. It typically weighs between 20-40 grams with an average size of 3 x 4 x 2 cm. The prostate is comprised of 70% glandular tissue and 30% fibromuscular or stromal tissue ^1-3and provides approximately 30% of the volume of seminal fluid.

The anterior surface forms the posterior wall of the retropubic space. The prostate is connected to the pubic bone by the puboprostatic ligaments ¹. Its inferolateral surface rests on the levator ani fascia ³. Its triangular and flat posterior surface is anterior to the rectum and has a vertical median groove. It is separated from the rectum by the rectovesical fascia. This is palpable via a rectal exam.

The seminal vesicles are superior and posterior to the prostate gland. Its ejaculatory ducts pierce the posterior surface of the prostate below the bladder ^1-3.

The prostate is comprised of three distinct zones with different embryologic origins:

peripheral zone
central zone
transition zone

The peripheral zone accounts for approximately 70% of the total prostate volume. The peripheral zone surrounds the distal urethra at the apex of the prostate and extends posterolaterally to the base. The peripheral zone is deficient anteriorly. This area is filled by the anterior fibromuscular stroma. The central zone takes up 25% of the prostate volume and contains the ejaculatory ducts. The transition zone takes up the remaining 5%. It is predominantly anterolateral to proximal urethra ^2-4.

The prostate gland has a true capsule and a fibrous pseudocapsule. The true capsule is a thin layer of connective tissue at the periphery of the prostate gland. The pseudocapsule is formed by 3 distinct layers of fascia; the anterior, lateral, and posterior fasciae. The anterolateral fascia is in direct continuity with true capsule. Laterally the fascia fuses with levator fascia. The prostatic venous plexus lies between the true capsule and pseudocapsule ^1-3.

Neurovascular bundles travel posterolaterally at 5 and 7 o'clock and give off branches into the prostate at the apex and base ⁵.

Relations

anteriorly: pubic symphysis
posteriorly: rectum
superiorly: bladder
inferiorly: urogenital membrane
laterally: prostatic venous plexus and levator ani

Blood supply

arterial supply
- prostatic branch of inferior vesical artery, a branch of the internal iliac artery
- sometimes supplied by the middle rectal arteries
venous drainage: prostatic venous plexus in communication with the pudendal plexus to the deep dorsal vein (to the internal iliac vein) with some communication to the Batson vertebral venous plexus ^2,3,5

Lymphatic drainage

drainage mainly to obturator and internal iliac nodes
some drainage to external iliac, presacral and para-aortic nodes ^1-4

Innervation

parasympathetic (S2-S4) and sympathetic (L1-L2) pelvic nerve plexus

Radiographic features

Ultrasound

best assessed with transrectal ultrasound
some zonal anatomy distinguishable
outer gland (central and peripheral zones) - uniform low echogenicity but usually more echogenic than the inner gland ^6,7

CT

poor for assessment of prostate zonal anatomy and pathology
with adjusted window settings
- central zone appears hyperdense between 40-60 HU
- peripheral zone appears hypodense between 10-25 HU
- useful staging metastatic spread ^4,6,8

MRI

preferred imaging modality
T1: homogenous intermediate signal intensity
T2
- anterior fibromuscular stroma is low T1W and T2W signal
- peripheral zone is high T2W signal, similar to or greater than adjacent fat
  - there are age related increases in T2W signal
- central and transitional zones are lower T2W signal than peripheral zone
- true capsule is a thin rim of low signal intensity
- distal urethra is a low intensity ring ^4,5