Endometriosis (diagrams)

Figure 1: etiology

Metastatic Theory

• Transplantation of endometrial tissue from the uterus to an ectopic location 
• Most widely accepted mechanism is retrograde menstruation but other theories include lymphovascular spread & iatrogenic implantation
• Evidence supporting retrograde menstruation:
  • Laparoscopic documentation
  • In vitro growth of shed endometrium in peritoneal fluid
  • In vivo growth of deliberately implanted endometrial cells in subcutaneous fat
  • Anatomic distribution of disease within dependent areas of the pelvis
  • Higher frequency of endometriosis in women with excessive retrograde flow (due to obstructive Mullerian duct anomalies)

Metaplastic Theory

• Metaplastic differentiation of celomic epithelium lining the pelvic peritoneum or Mullerian remnant tissue into functioning endometrial cells
• Proposed mechanism for rectovaginal endometriosis
• Evidence supporting metaplastic theory
  • Endometriosis in men (rare)
  • Endometriosis in women lacking functional eutopic endometrium (ie Turner’s syndrome, uterine agenesis)

Induction Theory

• Shed endometrium releases substances that induce undifferentiated mesenchyme to form endometriotic tissue
• Retroperitoneal endometriosis is thought to be caused by metaplasia of Mullerian remnants located in the rectovaginal septum and is sub-classified into groups according to location. Retroperitoneal disease may be confused by massive disease in the deepest portions of the pouch of Douglas, buried deep to adhesions.

Figure 2: implant morphology

• retroforniceal implants (65%)
  • typically a small lesion that develops from the posterior fornix toward the rectovaginal septum but not through it
• hourglass-shaped implants (25%)
  • larger lesions (>3cm) that originate from a retroforniceal location and extend toward the anterior rectal wall
• rectovaginal septal implants (10%)
  • typically a small lesion, separate from the cervix, located under the peritoneal fold of the cul-de-sac of Douglas

Figure 3: location of implants