Endometriosis is the presence of endometrial glands and stroma
(normal components of the tissue that normally lines the uterine
cavity) outside the body of the uterus. Most often, endometriosis
is located in the pelvis near or on the reproductive structures.
However endometriosis can occur in virtually any tissue of the
body, including distant sites like the lung, the knee and the
The two major clinically important problems associated with endometriosis
are infertility and pelvic pain. A common area of misunderstanding
relates to whether these symptoms are linked to each other. The
presence of infertility or pain can occur independent of each
other. That is, a patient can have incapacitating pain due to
endometriosis and normal fertility. Also, a patient can have infertility
associated with endometriosis with absolutely no pain at all.
This fact frequently surprises couples but is commonly seen by
There are no reliable nonsurgical diagnostic tests for endometriosis.
The diagnosis of pelvic endometriosis requires surgery. Ultrasonography
shows no specific pattern for pelvic endometriosis, but is often
helpful in diagnosing persistent nonfunctioning ovarian cysts
that may represent endometriomas. Although some specialists seem
to think that they can diagnose an endometrioma with certainty
using ultrasound, there are abundant scientific reports confirming
the nonspecific nature of the ultrasound for this purpose. MRI
also has no specific findings, with a reported sensitivity and
specificity of only about 60% for discovery of endometriosis.
Blood tests for CA 125 may be elevated with endometriosis, but
are also elevated with a tremendous number of other pelvic inflammatory
processes so an elevated CA 125 in a reproductive age woman has
little value (unless possibly used as a tumor marker when following
a patient with known cancer).
Endometriotic lesions depend upon stimulation by estrogens. The
lining of the uterus (endometrium) is one of the most complex
tissues in the body in that it continuously changes (grows, modifies
its structure, alters its own production of molecular messengers)
in response to stimulation by circulating sex steroids. Endometriosis
is rarely found in low estrogen environments, such as prior to
puberty, after menopause, or following surgical "castration."
Endometriosis discovered after menopause is almost always associated
with hormone replacement medication containing estrogens.
The incidence of endometriosis is not known, since the only reliable
way of determining its presence is through surgery or at autopsy.
Surgical incidence is biased by the selection process bringing
the patient to the operating room. No large cadaver study examining
autopsy specimens for endometriosis has reported data that has
been widely accepted. Despite this uncertainty, widely used numbers
for the incidence of endometriosis include 3-10% of all reproductive
age women and 25-40% of all women with an infertility problem.
The finding that endometriosis is very often found in areas near
the end of the tube and in the cul de sac behind the uterus (as
well as other dependent regions of the pelvis) has suggested that
retrograde flow (from the uterus through the tube into the pelvis)
of menstrual blood and cellular material during menses is an important
variable in determining which women will develop endometriosis.
There are three main theories for the mechanism causing endometriosis.
Each theory has many supporters. It may be that each of these
three may accurately describe one of several possible mechanisms.
In the 1920s a physician named John Sampson devoted a great deal
of time to the study of endometriosis and is widely credited with
the initial suggestion that retrograde flow is the primary path
for this tissue to grow in the pelvis. His reasoning was based
on the distribution of implants that he observed. Additional support
for this theory has been collected over the years and includes
- * virtually all women undergoing laparoscopy at the
time of menses can be seen to have blood flowing from the fimbriated
end of their fallopian tubes (retrograde flow)
- * the most common sites for endometriosis at both laparotomy
and laparoscopy are in dependent portions of the pelvis and close
to the ends of the tubes
- * when recovered surgically and grown in culture endometrial
fragments within menstrual blood have the potential to survive
- * a higher incidence of endometriosis is observed in
women who have obstructions to the normal downward flow (out through
the vagina), forcing a greater percentage of flow through the
tube in a retrograde fashion
- * there is an increased risk of endometriosis if the
woman has a shorter intermenstrual interval, longer duration flow
or larger volume of flow
- * in female monkeys where the uterus has been surgically
transposed (turned around) so that the flow is predominantly into
the abdomen rather than out the vagina there is a higher incidence
One interesting question regarding this information is "if
virtually all women have retrograde flow of endometrial cells
into their pelvis during each menses then why don't virtually
all women have endometriosis?" The answer to this question
is not known, however, there are several proposed theories. The
most widely accepted theory concerns the immune system. Basically,
the immune system can be thought of as a housekeeping mechanism
that rejects or destroys any tissue that is "foreign."
It can also regulate where a tissue will be allowed to grow within
When the immune system is activated an inflammatory response occurs
and these inflammatory cells help to reject the abnormally placed
tissues. If there is a problem with the immune response then tissue
might be allowed to grow in abnormal locations, that is, to form
implants such as endometriosis. In theory, if the amount of tissue
is very large it may overwhelm the available normally functioning
immune response and result in the growth of this tissue in abnormal
locations. Therefore, endometriosis may occur either when a defective
immune system is presented with a normal amount of retrograde
flow or a normal immune system is presented with a large amount
The presence of endometriosis in sites distant from the adnexae
(ovaries and tubes) has led to alternative theories. The two other
theories commonly considered propose that
- * vascular spread of tissue (via the blood vessels
or lymphatics supplying the uterus) from the uterus to distant
sites allows tissue to be transported to areas like the lungs
or the knee, and
- * metaplasia (change from one normal type of tissue
to another normal type of tissue) of the coelomic epithelium (type
of tissue lining the pelvic structures where endometriosis is
commonly found and from which uterine endometrial cells are normally
derived) allows endometrial tissue to replace other types of tissues
outside the uterus. This theory is supported by the finding of
endometriosis in some men who have received estrogen treatments,
where no endometrial tissue normally exists.