Q&A on cutaneous endometriosis

To my understanding cutaneous endometriosis is most commonly found at the sites of previous surgical incisions. Before considering surgical incision endometriosis in more detail, are there also cases of cutaneous endometriosis in the absence of a scar/incision, and if so, where do these lesions most commonly occur?
To my knowledge, besides cases of spontaneous endometriosis involving the umbilicus, the only instance of cutaneous endometriosis unassociated with a surgical scar was of the vulva in a nulligravida (Healy JJ. Bilateral endometriosis of the vulva. Am J Obstet Gynecol 1956;72:1361-3.

In the example of umbilical endometriosis, is there almost always a prior incision through the umbilicus prior to formation of disease or does disease at this site tend to be spontaneous?
Umbilical endometriosis can occur spontaneously and I would guess that most cases of umbilical endometriosis are spontaneous. There are sporadic reports of umbilical endometriosis occurring after laparoscopic hysterectomy with use of an umbilical trocar. In 2 such cases, strips of endometrium and myometrium were removed through an unprotected umbilicus (the trocar sheath had been removed and the tissue was pulled through the hole in the umbilicus). (Koninckx PR et al. Umbilical endometriosis after unprotected removal of uterine pieces through the umbilicus. J Am Assoc Gynecol Laparosc 2000; 7:227-32.)

What are the symptoms of cutaneous endometriosis and at what age would this form of disease most commonly present? Does it typically worsen over time? Is cutaneous endometriosis associated with disease elsewhere or can it present in isolation, as the sole site of disease?
Cutaneous endometriosis presents as a small, painful lump which may grow slowly in size. Many lesions seem to attain a certain size and stop growing, although since they are typically removed surgically, it would be impossible to state that they have completely stopped increasing in size. Cyclic peri-menstrual swelling and pain of the affected site is the most common symptom of cutaneous endometriosis. The umbilicus is the thinnest part of the abdominal wall, perhaps 1/4 inch thick, even in obese people. Going from outside in, the layers of the umbilicus are: epidermis, dermis, fascia, retroperitoneal fat, and peritoneum. Because the thickness of the abdominal wall at the umbilicus is so thin, umbilical endometriosis may also be associated with a cyclic bloody discharge. Endometriosis of a surgical scar (the most common form of cutaneous endometriosis) usually does not affect the dermis and epidermis (the layers of the skin) as umbilical endometriosis can, so bloody discharge would be rare, if it ever occurred at all. Endometriosis of the surgical scar usually affects the fascia primarily, with some fibrosis of the subcutaneous fat overlying the fascia. Endometriosis of the surgical scar rarely has any connection deeper into the peritoneum or peritoneal cavity.

In the case of endometriosis forming at the sites of scars, what are the possible causal mechanisms (i.e. transplanted endometrial tissue 'caught' in the incision and/or healthy tissue undergoing transformation into endometriosis as a result of the chemicals released during the process of wound healing).
The two putative causal mechanisms of endometriosis of a surgical scar are autotransplantation (inoculation of the scar by endometrial tissue fragments from the uterine lining) and metaplasia related to the chemicals released by the body during surgical healing, including various growth factors. One factor voting against autotransplantation is that the histology of scar endometriosis is usually not well differentiated like native endometrium would be. One might suspect that an autotransplant would remain more identical to the tissue of origin. Another factor voting against autotransplantation is the propensity of scar endometriosis to involve primarily the fascia - if inoculation of an entire open surgical scar occurred, one might expect that scar endometriosis might be more uniformly distributed from the skin down to the peritoneum, not just primarily involve one layer. It is clear that every cell in the body has the genetic material to form any other tissue type, given the proper stimulus, so every cell in the body can be a 'stem cell'. By the concept of Mülleriosis, tracts of tissue may be laid down in the body which either contain endometriosis already or which possess an increased capability of undergoing metaplasia into endometriosis. In the pelvis, these tracts of tissue are most commonly found in the posterior pelvis but may occur elsewhere in the pelvis, bowel, or bladder. But these tracts of tissue can theoretically be found anywhere else in the body, although with a frequency which is inversely proportional to the distance of a tract from the cul-de-sac. By this concept, the abdominal wall could have patterned tracts of tissue, with patterning most common on the lower abdominal wall near the pelvis. The umbilical arteries and veins pass through the umbilicus in the fetus. In female fetuses, these vascular structures arise from the uterine arteries and veins. Therefore, the umbilicus has a rather direct and shared formative connection to the pelvis which may exceed the patterning of the abdominal wall which may be associated with scar endometriosis not involving the umbilicus. This ontologic aspect of the umbilicus may increase the possibility that a tract of Müllerian tissue had been laid down within the umbilicus compared to elsewhere on the abdominal wall. If a tract of Mülleriosis-affected tissue were laid down within the umbilicus, the umbilicus could eventually display either spontaneous endometriosis (if endometriosis had been laid down here during embryogenesis), or scar endometriosis related to laparoscopy due to metaplasia of such a tract which had been stimulated by the growth factors associated with wound healing and tissue repair. Such a tract of tissue might be more prone to develop endometriosis by metaplasia related to wound healing from one or repeated insertions of umbilical trocars for laparoscopy than a trocar site which is not involved by a tract of tissue affected by Mulleriosis.

Are certain types of scars more associated with a given pathogenesis than others?
Scar endometriosis has been reported with transverse laparotomy incisions, vertical laparotomy incisions, trocar insertion sites in the umbilicus, amniocentesis needle tracts, and episiotomies. Scar endometriosis involving laparotomy scars seems to follow patterns - with transverse incisions, the endometriosis is only occasionally found in midline, but found far more commonly off to one side - the right seemingly more common. This right-sided predilection for scar endometriosis mirrors the right-sided predilection for inguinal endometriosis, suggesting that the right abdominal wall is more commonly patterned than the left. With vertical incisions, scar endometriosis is found closer to the pubic bone than the umbilicus, suggesting that the patterned tracts are more prevalent nearer the pelvis. Most scar endometriosis in laparotomy scars involves just one nodule of endometriosis.

Would transplanted tissue in the case of scar endometriosis afford support for the implantation theory by supporting the notion that native endometrium can implant and invade in areas outside the uterus? Is scar endometriosis a proxy model for Sampson's theory of reflux menstruation as the origin of endometriosis?
Sampson's theory of origin of endometriosis revolves around menstrual endometrium implanting on peritoneal surfaces. Most cases of scar endometriosis are not associated with sloughed menstrual endometrium, but connote the possibility that viable endometrium was inoculated into a fresh, receptive surgical scar. This would suggest that scar endometriosis is not a particularly apt proxy for proof of Sampson's theory. Another point has been mentioned above - laparotomy scar endometriosis manifests as a single nodule in most cases. I never encountered a case where more than one nodule was present. If inoculation of an 8 - 10inch long surgical scar were to occur, one would expect that some patients would have more than one nodule. So laparotomy scar endometriosis cannot be accepted as a good model of the correctness of Sampson's theory. Laparoscopic trocar tracts or amniocentesis needle tracts are single points at which one would expect only a single nodule to develop. If such a single nodule of scar endometriosis were observed without knowledge of the patterning of scar endometriosis in laparotomy scars, it would be easy to jump to a quick conclusion that inoculation of the tract by endometrium had occurred. In summary, laparotomy scars represent a better 'laboratory' for study of scar endometriosis than single puncture sites. Whether established pelvic endometriosis could be inoculated into a surgical wound is unknown.

When scar endometriosis is present, does the disease tend to only involve the outer surface of the skin or can it permeate the full thickness of the abdominal wall or even form a tract from the outside to the inside or vice versa?
As answered above, scar endometriosis mainly involves the fascia.

How is cutaneous endometriosis best treated?
Personal experience and the published literature make it clear that wide local excision is curable in the vast majority of cases.

Is it readily treatable surgically?
Yes, it is easy to operate on the abdominal wall. Usually the surgery does not extend into the abdominal cavity. When it does, the entry area is rather small compared to the original laparotomy incision.

Are some variants more treatable than others?
All are equally easy to treat since no vital structures are involved. Cosmetic repair of the umbilicus is a little more difficult than simply closing up the skin over a laparotomy nodule.

If scar endometriosis can form purely as a result of the process of healing (tissue undergoing metaplasia into endometriosis under the influence of the cellular environment present during wound healing), what is to prevent this same process from recurring after the affected area has been excised and the newly created incision re-heals?
The tract of tissue which had been laid down embryologically has now been removed. Such tracts of tissue are not necessarily sheets of contiguous tissue resembling highways, although some might be. Some tracts of substrate tissue may be spotted intermittently here or there across a region which has been previously patterned.

What measures can be taken during surgery to reduce the risk of endometriosis forming at excision sites?
If scar endometriosis is due to stimulation of embryologically-patterned tracts, there would be no obvious prevention, since the wound healing process would have to be disrupted. Given the rarity of scar endometriosis - most women with laparotomies or laparoscopies will never develop it - it would make no sense to try to interfere with the wound healing process in 100% of patients to prevent scar endometriosis in <0.5% of patients. If scar endometriosis were due to inoculation of the surgical wound, then placing some type of barrier over each layer of the abdominal wall (especially the fascia) before conducting surgery within the peritoneum might make sense. But the question arises again - do you go to the effort and expense on 100% of patients to protect <0.5% of them from a benign, relatively easily treated problem? I'm sure some medical equipment company would say yes.

Can endometriosis form (by metaplasia) or become part of (by incomplete excision) the vaginal cuff after hysterectomy? If so, what symptoms would that invoke (pain, cyclical bleeding)?
The tissue of the vaginal wall is stratified squamous epithelium, just like the skin. The differences are that the vaginal wall has no hair follicles or sweat glands. Therefore, every comment made about scar endometriosis of the skin applies to the vaginal wall. The posterior vaginal fornix behind the cervix is the most common area for vaginal endometriosis to occur, usually associated with a nodule of the rectum with obliteration of the cul-de-sac, or a nodule of the uterosacral ligament. If the normal-appearing posterior vaginal fornix is not removed with a nodule of the rectum or of a uterosacral ligament, there is a chance that it can still form vaginal endometriosis later, as if a patterned tract of substrate tissue remained in place and manifest endometriosis later. Prof. Donnez in Belgium observed this and to decrease post-op recurrence (by what might appear to be metaplasia), he recommends that the posterior fornix be removed routinely when a nodule in the vicinity is being removed. Getting back to specifically answering the question, my guess is that most vaginal scar endometriosis is related to an adjacent nodule which was not removed and the endometriosis simply got incorporated into the vaginal cuff during suture closure.

Questions by Libby Hopton and answers by Dr. David Redwine