December 12, 2022
by Mr Martin Hirsch (Consultant Gynaecologist & Endometriosis Specialist)

Endometriosis is the most common cause of chronic pelvic pain in women. Below is an overview of the normal anatomy and physiology of the female reproductive system and what happens in endometriosis, including its complications and how it can be treated.

Anatomy of the female reproductive system

The female reproductive system is comprised of:

  • Two ovaries (right and left);
  • Two fallopian tubes (right and left);
  • The uterus (including cervix); and
  • The vagina.

Ovaries & fallopian tubes

The ovaries lie either side of the uterus, attached to the posterior surface of the broad ligament of the uterus. The ovaries produce eggs (oocytes) and the hormones progesterone and oestrogen. When an ovary produces an egg, it travels down the fallopian tube where, if sperm is present, it may become fertilised. The fallopian tubes transport the egg to the uterus.


The uterus lies in front (anterior) of the rectum and above and behind (posterosuperior) to the bladder. The uterus is mostly supported by the pelvic floor muscles, but is also supported by several ligaments, including the broad ligament, round ligament, and ovarian ligament. It has thick muscular walls and can be divided into three portions:

  • Fundus – the top of the uterus, above where the fallopian tubes join;
  • Body – the usual site of implantation of the fertilised egg; and
  • Cervix – the lowest part of the uterus.

The fundus and body of the uterus are histologically very similar, being comprised of three layers of tissue:

  • Serosa – the most outer layer.
  • Myometrium – the thick, middle, muscular layer.
  • Endometrium – the inner, mucous membrane, which can also be divided into:
    • Deep stratum basalis – does not change during the menstrual cycle and is not shed during menstruation.
    • Superficial stratum functionalis – this becomes a much thicker layer in response to oestrogen, ready for a fertilised egg to implant, and is shed during menstruation.

The cervix connects the uterus to the vagina, allowing sperm to pass into the uterus and maintaining a sterile environment in the uterus.


The vagina is the final organ of the female reproductive tract, serving as a passage for sexual intercourse, menstruation, and childbirth. The vagina lies behind (posterior) to the bladder and urethra, and in front (anterior) of the rectum and anal canal.

Physiology of menstruation

The menstrual cycle can be divided into two phases:

  • Proliferative (follicular) phase.
  • Secretory (luteal) phase.

The proliferative phase involves rising levels of oestrogen and proliferation (growth and increase in the number of cells) of the endometrial layer of the uterus. At the end of this phase, ovulation usually occurs i.e., an egg is released from an ovary.

The secretory phase involves high levels of progesterone released from the ovary, which causes the endometrial layer to stop proliferating, become more complex, accumulate energy sources, and gain a greater surface area of bloody supply. If the egg does not become fertilised, the hormone levels drop and the endometrial layer is no longer able to be maintained. This then results in it being expelled from the uterus into the vagina. This is known as menses or a ‘period’.

What is endometriosis?

Endometriosis is a chronic condition involving the development of endometrial-like tissue outside the uterus. Endometriosis is regulated by hormones in a similar way to the endometrium which we discussed earlier. During a person’s period the endometriosis will bleed and become inflamed; this can lead to adhesions. The cause of endometriosis is still not entirely understood but theories include:

  • Retrograde menstruation – menstrual blood containing endometrial cells flows up through the fallopian tubes and outside the uterus into the pelvis.
  • Cellular metaplasia – cells outside the uterus change from their original type to the endometrial type, normally under the influence of hormones.
  • Spread in the blood or lymphatic system – it is believed that endometriosis found in lung, nose, or wrist may have been transported to these locations via the blood or lymphatic systems.

Endometriosis is commonly found on the lining of the pelvis (peritoneum) and the ovaries, but can also occur in the fallopian tubes, bowel, bladder, and ligaments within the pelvis. Although rare, endometriosis can also develop in the pleura (lining of the lungs), pericardium (lining of the heart), diaphragm, and central nervous system.

Endometriosis lesions have three common sub-types:

  • Superficial endometriosis – lesions on the pelvic peritoneum (lining).
  • Ovarian endometriosis – endometriomas.
  • Deep endometriosis – nodules of endometriosis > 5mm, commonly located in the recto-vaginal space, bladder, bowel, and ligaments behind the uterus.

What are the signs and symptoms of endometriosis?

Endometriosis is most common in young women, affecting approximately 10% of all females of reproductive age around the World.

Typical symptoms of endometriosis include:

  • Painful periods (dysmenorrhoea)
  • Chronic pelvic pain
  • Pain during/after sexual intercourse
  • Pain when passing urine (associated with menstruation)
  • Pain when passing bowel movements (associated with menstruation)
  • Fatigue
  • Depression and anxiety
  • Nausea
  • Bloating

How is endometriosis managed?

The National Institute for Health and Care Excellence (NICE) have produced three key statements regarding the management of individuals with confirmed/suspected endometriosis:

“Statement 1: Women presenting with suspected endometriosis have an abdominal and, if appropriate, a pelvic examination.

Statement 2: Women are referred for an ultrasound or to a gynaecology service if they have:

  1. Severe, persistent, or recurrent symptoms of endometriosis
  2. Initial hormonal treatment for endometriosis is not effective, not tolerated or contraindicated.

Statement 3: Women with suspected or confirmed deep endometriosis involving the bowel, bladder or ureter are referred to a specialist endometriosis service.”

NICE, 2018b

At local gynaecology or specialist centres, laparoscopic investigation may be discussed; however this is an invasive procedure and carries risks. The individual should be promptly referred to an endometriosis specialist service if there is suspicion of deep endometriosis involving the bowel, bladder, ureters or if endometriosis is suspected outside the pelvis.

Pain related to endometriosis should be first managed with a short course of paracetamol and/or non-steroidal anti-inflammatories, such as ibuprofen. Hormonal treatment may also be offered by way of the oral contraceptive pill (combined or progesterone-only), contraceptive implant, contraceptive injection, or the contraceptive coil (intrauterine device (IUD)). After three-six months of initial treatment, the individual should be reviewed and, if symptoms are persistent, they should be referred to a gynaecology service.

What are the surgical management options for endometriosis?

The decision to undergo surgical management of endometriosis should be carefully combined with detailed discussion regarding the individuals’ thoughts, feelings, and ideas surrounding fertility and pain management.

In individuals who wish to try and preserve fertility, the surgical approach should be performed following multidisciplinary team input, including fertility experts, and diagnostic fertility tests and fertility treatments should be discussed with the individual. Key issues to be discussed include:

  • How laparoscopic surgery may affect the chance of future pregnancy;
  • The potential impact on ovarian reserve;
  • The potential impact complications may have on fertility; and
  • What alternatives to surgery are available.

During an investigatory laparoscopy to diagnose endometriosis, treatment should be considered if there is the presence of peritoneal endometriomas (not involving the bowel, bladder, or ureter) or uncomplicated ovarian endometriomas. These may be treated with laparoscopic excision (surgical removal) or ablation (destruction of the tissue with an energy device); excision should be used over ablation in cases of endometriomas where the individual wishes to enhance spontaneous fertility. This needs to be considered individually based on a women’s ovarian reserve.

In severe cases, where fertility does not wish to be preserved, a hysterectomy (removal of the uterus) with or without a salpingo-oophorectomy (removal of the ovaries and fallopian tubes) may be performed. This is a major invasive surgery with a prolonged recovery period.

What are the complications of endometriosis?

Endometriosis can cause many complications:

  • Chronic pain
  • Fertility difficulties
  • Adhesions, leading to:
    • Kidney Obstruction
    • Bowel obstruction
    • Chronic pain
  • Ovarian cysts (endometriomas)

In uncommon cases, endometriosis can lead to small holes developing in the diaphragm. These holes allow air and fluid to pass into the pleural cavity leading to catamenial pneumothorax – pneumothoraxes which occurs 72 hours before or after the onset of menstruation.

If you experience any pain symptoms that coincide with your period, we suggest seeing your GP or an endometriosis specialist. Mr Martin Hirsch (Consultant Gynaecologist) is an Endometriosis Specialist and a Medico-Legal Expert Witness. He is able to provide his expert opinion on breach of duty, causation, current condition, and prognosis.

To explore how Mr Hirsch may be able to assist with a medico-legal case, please click here.

To explore how Mr Hirsch may be able to assist an individual requiring treatment for endometriosis, please see his private practice here.