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prostate

Thursday 8 December 2016

normal prostate

Pathology

- prostatic pathology / prostate pathology

Synopsis

- Function: conduit for urine, adds nutritional secretions to sperm to form semen during ejaculation
- 20 g, funnel shaped, 4 x 3 x 2 cm
- Within true pelvis between bladder neck (base of prostate) and urogenital diaphragm / levator ani muscle (apex of prostate)
- Apex contains some muscle fibers from urogenital diaphragm
- Seminal vesicles extend from posterior prostate to posterior surface of bladder
- Ampulla of Vas (ductus) deferens and terminal seminal vesicle duct form ejaculatory duct, join prostatic utricle to open into prostatic urethra
- Denonvillier’s fascia (aka rectovesicle septum): thin layer of connective tissue that separates prostate and seminal vesicles from rectum
- Prostatic urethra begins on superior surface, descends almost vertically, with continuous prostatic utricle extending to posterior prostatic wall, exits anteriorly; divided into halves by sharp 35 degree angle midway, at site of verumontanum (bulge along posterior proximal urethra; site of emptying of ejaculatory, central and transition zone ducts)
- Peripheral zone ducts empty into distal urethra
- Prostatic nervous plexus supplies prostate, seminal vesicles, corpus spongiosum, corpora cavernosum and urethra; nerves distributed evenly in apex, mid gland and base of prostate, AJCP 2001;115:39

Anatomical models

- Embryologic model: 5 lobes: 2 lateral plus posterior, middle, anterior lobes
- Other model (not used): 2 lateral lobes, small median lobe (contains posterior lobe, forms floor of urethra)
- Current model (McNeal): transitional, central, peripheral, periurethral zones
- McNeal zones
- Outer (cortical) zones are termed “peripheral” and “central”; central is towards base
- Inner (periurethral) zone is termed “transitional”

Histology

- Transition zone

  • 5% of prostatic volume; 2 pear shaped lobes surrounding proximal urethra
  • Site of nodular prostatic hyperplasia, may expand to bulk of gland
  • Site of 10% of prostate cancers (large duct carcinomas)
  • Contains moderately compact fascicles of smooth muscle

- Central zone

  • 25% of prostatic volume; surrounds transition zone to angle of urethra to bladder base
  • Site of 5% of prostate cancers
  • Unlike peripheral and transition zones, ducts are large and irregular; glands are complex with tall columnar, pseudostratified, papillary infoldings; striking basal cell layer with eosinophilic cytoplasm
  • Stroma is densest in central zone, least dense in peripheral zone, in between for transition zone (Hum Path 2002;33:518)

- Peripheral zone

  • 70% of prostatic volume, from apex posterior to base, surrounds transition and central zones
  • Site of 80% of prostate cancers
  • Has loose fibromuscular stroma with widely spaced smooth muscle bundles, moderate gland complexity

- Prostatic non-glandular tissue

  • “Capsule”: fibromuscular layer most prominent along base and posterior portion of lateral borders; an inseparable component of prostatic stroma, not a distinct capsule, (AJSP 1989;13:21)
  • Along lateral borders, fibrous septa traverse periprostatic fat and merges with fibromuscular stroma
  • Anteriorly, prostatic stroma merges with fibromuscular tissue of urogenital diaphragm
  • Stroma contains abundant smooth muscle, which duplicates function of myoepithelial cells in breast; i.e. squeezes out secretions

- Prostatic glandular tissue

  • Prostate glands found normally within skeletal muscle at apex, anteriorly, and in distal posterolateral gland
  • Secrete normal mucins, produce pigment (lipofuscin), are androgen sensitive (castration causes atrophy); differentiation and growth is androgen dependent
  • Large prostatic ducts have single layer of urothelial-like epithelium without umbrella cells, which is PSA/PAP positive; may undergo squamous metaplasia with estrogen therapy
  • Benign tissue may contain hyaline globules (degenerative, aka thanatosomes, AJSP 2003;27:700), may be adjacent to skeletal muscle or nerves

Type of cells

secretory cells, basal cells, scattered neuroendocrine cells, urothelium, ejaculatory duct/seminal vesicle type cells

- Secretory cells

  • Located along glandular lumen
  • Positive stains: prostatic acid phosphatase (PAP), prostate-specific antigen (PSA), vimentin, keratin (some), Leu7/CD57, EMA (80%), CEA (25%)
  • Negative stains: CK903 (34 beta E12, high molecular weight keratin)

- Basal cells

  • Separate secretory cells from basement membrane; consist of low cuboidal epithelium and columnar mucus secreting cells; may have prominent nuclear groove, prominent nucleoli
  • May be reserve cells (stem cells), can undergo myoepithelial metaplasia but are NOT myoepithelial cells
  • Their presence differentiates benign conditions (basal cells are present) from well differentiated adenocarcinoma (not present)
  • Positive stains: CK903 (34 beta E12 / high molecular weight keratin), p63, androgen receptors
  • Negative stains: PSA, PAP, S100, actin

- Neuroendocrine cells

  • Irregularly distributed
  • Positive stains: chromogranin A, B, secretogranin II, peptide hormones, PSA
  • Negatives stains: androgen receptors

- Urothelium

  • In proximal 2 mm of prostatic ducts

- Ejaculatory ducts and seminal vesicles

  • Lined by double cell layer of pseudostratified epithelium, contain lipofuscin (golden-brown pigment), have large, hyperchromatic nuclei (also called "monster" nuclei), may have intranuclear inclusions

- Mucins

  • Normal mucins are neutral; most adenocarcinomas secrete acidic and neutral mucins

- Glandular secretions

  • Can identify with glutaraldehyde based fixatives, fill the normal secretory cell cytoplasm, distinct bright red on H&E staining because of high polyamine content; also present in penile urethra, (Hum Path 2002;33:905)