Endometriosis is defined as the presence of actively funcitioning endometrium in any part of the body other than its normal position of lining the endometrial cavity( lining of the uterine cavity-inside the uterus).

The term endometriosis was first coined by Samson in 1921.

What is the difference between endometriosis and adenomyosis?

Adenomyosis refers to the presence of endometrial tissue within the myometrium (The uterine muscles -The muscles that make up the uterus), while endometriosis refers to the presence of functioning endometrial tissue outside the uterus.

What are the common sites/organs involved in endometriosis?

Endometriosis is most commonly found in the pelvis (surface of the ovary, broad ligaments, pelvic peritoneum and fallopian tubes).

Other sites where endometriosis may be found include: heart, lungs, pleura, eyes, upper limbs, skin, lymph nodes

Incidence of Endometriosis

The exact incidence and prevalence of endometriosis is not well known. 

Endometriosis has been found in 10 to 33 percent of gynaecological laporatomies.

90% of the women diagnosed with endometriosis are between the ages of 20 and 50 years.

With the use of advanced laporoscopic biopsy  it is now possible to identify endometriosis much earlier in life.

The increasing prevalence of endometriosis is probably due to advanced diagnostic techniques and increasing awareness of the disease rather than an increase in the disease itself.

There is a much higher incidence of endometriosis among Japanese women. 

It is more common among caucasian women compared to black women.

Endometriosis is common among the upper class of society (High socioeconomic group) . This is attributed to late marriage , which means the woman has had much more menstrual cycles and therefore higher chances of having endometriosis.

There is also a familial tendency to have endometriosis (Genetic basis basis of endometriosis?) .

Aetiology and Pathogenesis of Endometriosis (Causes)

Several theories have been suggested in the pathogenesis of endometriosis.

The lymphatic and haematological dissemination theory

This theory suggests that endometrial cells are carried by blood and lymphatics and implanted in other parts of the body. This could explain the occurrence of endometriosis in the lymph nodes, chest and axilla.

The coelomic metaplastic theory

This tries to explain the occurence of endometriosis as an early event during embryogenesis.

This theory suggests that there is abnormal differentation of coelomic epithelium ,which leads to the development of endometriosis anywhere in the coelomic epithelium .

This is the only theory that can explain the presence of endometriosis in males and in women who do not have uterus.

The Implantation Theory

Also known as the retrograde menstruation theory.

It tries to explain the occurence of endometriosis in the pelvis.

It was first postulated by Samson (1927).

He suggested that the endometrium could flow retrogradely through the fallopian tubes to  the pelvis during menstruation. It also explains the higher incidence of endometriosis in the pelvis compared to other sites.

This theory is supported by the fact that women without uterus do not develop pelvic endometriosis.

The occurence of endometriosis in abdominal surgical scars are due to the endometrial cells deposited in the skin during surgery.

Direct extension 

The direct growth of endometrium through the tissue space to the myometrium is thought to cause adenomyosis.

The clinical features and management will be discussed in a seperate topic.

References:

Dewhurst’s Textbook of Obstetrics and Gynaecology for Postgraduates. Sixth Edition by D Keith Edmonds.

Textbook of Obstetrics and Gynaecology for Medical Students by Akin Agboola et al 2 nd Edition .

Gynaecology by Ten Teachers .Edited by Stuart Campbell and Ash Monga, 17th edition.

Clinical Gynaecology for Undergraduates compiled by Dr WDN De Alwis, Dr R Gnanasekeram, Dr N. Gunawansa. Edited Prof. C Randeniya MBBS, MS, FRCOG. Senior Lecturer, Dept. of Obstetrics and Gynaecology, Faculty of Medicine ,Colombo. Consultant , De Soysa Hospital for Women and National Hospital of Sri Lanka.