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PH-RO01

Endometriosis

How tissue like the lining of the uterus grows outside it, bleeds and inflames with each cycle, and leaves scarring and adhesions that cause pelvic pain and can reduce fertility.

By the end, you can

  • Describe the layers of the endometrium and how they change through the menstrual cycle.
  • Outline the main theories of how endometriosis begins, and what each explains.
  • Explain how oestrogen, prostaglandins and repeated bleeding sustain inflammation in lesions.
  • Relate the site of lesions and adhesions to painful periods, deep dyspareunia and dyschezia.
  • Explain the mechanisms by which endometriosis can reduce fertility.
  • Recognise the classic appearances (powder-burn lesions, chocolate cysts), staging, tests and differentials of endometriosis, and explain how each main treatment acts on its mechanism.

What it is

Endometriosis is a chronic, oestrogen-dependent inflammatory condition in which tissue resembling the endometrium (glands and stroma) grows outside the uterus, most often on the pelvic peritoneum and ovaries. It is distinct from adenomyosis, in which endometrial tissue lies within the muscle of the uterine wall, although the two often occur together.

4 types to tell apart
Superficial peritoneal endometriosis
Small lesions on the surface of the pelvic peritoneum. Their colour varies from clear or red (newer, more active) to dark or white and scarred (older).
Ovarian endometrioma
A cyst in the ovary lined by endometrial-like tissue and filled with thick, altered blood (a “chocolate cyst”).
Deep endometriosis
Nodules extending more than about 5 mm beneath the peritoneum, typically in the uterosacral ligaments, behind the vagina, or in the bowel or bladder wall; often fibrotic and painful.
Extra-pelvic endometriosis
Rare lesions outside the pelvis, for example on the diaphragm, in the chest or in surgical scars.

US spelling: oestrogen → estrogen, oestradiol → estradiol.

Normal function

The endometrium and the menstrual cycle

The wall of the has three layers: the endometrium lining the cavity, the thick smooth muscle of the myometrium, and the outer perimetrium. The endometrium has a deep basal layer that persists and a superficial functional layer that is built up and shed each cycle. Its glands sit in a cellular stroma supplied by coiled spiral arteries.

Before ovulation, oestradiol from the growing follicles in the makes the functional layer proliferate. After ovulation, progesterone from the corpus luteum makes it secretory, ready for an embryo. If no pregnancy occurs, the corpus luteum regresses, progesterone falls, the spiral arteries constrict and the functional layer breaks down. Prostaglandins released as it breaks down also make the myometrium contract, which causes period cramps.

Most menstrual blood leaves through the cervix and vagina, but some flows backwards along the and out past the into the peritoneal cavity. This retrograde flow happens in most people who menstruate; usually immune cells in the peritoneum clear it.

Point to it on the model