seminal vesicle

**Anatomy** - Paired, coiled, tubular glands lying posterior to the bladder and superior to the prostate, lateral to the ampulla of the vas deferens. - The duct of the seminal vesicle unites with the vas deferens to form the **ejaculatory duct**, which pierces the prostate and empties into the prostatic urethra at the verumontanum. - Blood supply: inferior vesical and middle rectal arteries (branches of the internal iliac). Lymphatics drain to the internal iliac nodes. - Innervation: sympathetic (hypogastric nerve, T10-L2) causes **emission** (smooth muscle contraction). Parasympathetic (pelvic splanchnic nerves, S2-S4) causes erection and secretion. Somatic (pudendal nerve, S2-S4) causes **expulsion/ejaculation** via bulbospongiosus contraction.

**Embryology** - Derived from the **mesonephric (Wolffian) duct** under the influence of **testosterone**. This also gives rise to the epididymis, ductus deferens, and ejaculatory duct (mnemonic: **SEED**: Seminal vesicles, Epididymis, Ejaculatory duct, Ductus deferens). - Ureteric bud also arises from the mesonephric duct. - The prostate is NOT part of SEED. It derives from the urogenital sinus (endoderm) and is driven by DHT.

**Secretions (~60-70% of ejaculate volume)** - **Fructose**: the main energy source for sperm. Its presence in semen is used to assess seminal vesicle patency. - **Prostaglandins**: promote uterine and tubal smooth muscle contraction, aiding sperm transport, and suppress the female immune response. - **Semenogelins (I and II) and fibronectin**: form the coagulum (semen clotting). Prostate-specific antigen (PSA) later liquefies it. - Alkaline pH, which buffers the acidic vaginal environment. Also contains ascorbic acid and flavins (give semen its grayish/yellow color under fluorescence).

**Clinical correlations** - **Congenital bilateral absence of the vas deferens (CBAVD)**: associated with **CFTR** mutations (cystic fibrosis). It often comes with seminal vesicle hypoplasia or agenesis. The result is obstructive azoospermia with **low semen volume (<1.5 mL), low pH (acidic), and absent fructose**. Testicular spermatogenesis is normal. - **Ejaculatory duct obstruction**: also gives low volume, acidic semen, and absent fructose. Causes include cysts (Müllerian duct or utricle cysts), stones, and prior infection. Transrectal ultrasound is the diagnostic test. - **Seminal vesiculitis**: usually accompanies prostatitis or epididymitis. Organisms include E. coli and Chlamydia/Gonorrhea (in younger men). Presents with hematospermia, painful ejaculation, and perineal pain. - **Hematospermia**: usually benign and self-limited. Consider infection, trauma/instrumentation (prostate biopsy), and, rarely, malignancy in older men. - **Prostate cancer**: seminal vesicle invasion upstages the tumor to **T3b** and has prognostic significance (higher risk of recurrence and nodal disease). - **Retrograde ejaculation**: due to failure of bladder neck closure (e.g., diabetic autonomic neuropathy, alpha-blockers like tamsulosin, TURP, retroperitoneal lymph node dissection). It causes low or absent ejaculate volume and sperm in post-ejaculatory urine. - **Androgen dependence**: seminal vesicle size and secretion depend on testosterone. Hypogonadism gives low semen volume and low fructose. - **Zinner syndrome**: a rare Wolffian duct anomaly with the triad of seminal vesicle cyst, ipsilateral renal agenesis, and ejaculatory duct obstruction. - **Surgical note**: Denonvilliers' fascia separates the seminal vesicles and prostate from the rectum.

**High-yield board pearl**: Low-volume, acidic, fructose-negative azoospermia suggests absent or obstructed seminal vesicles/ejaculatory ducts (CBAVD or ejaculatory duct obstruction). Think CFTR testing.