by Tamer Seckin, MD Endometriosis Excision Surgeon / Seckin Endometriosis Center (SEC)
What is peritoneal endometriosis?
the American Society of Reproductive Medicine defines the present classification of endometriosis for patients who have fertility issues. It is a morphological classification that focuses strictly on the anatomical changes of specific areas, particularly the fallopian tubes and ovaries. It does not take into consideration one of the most important symptoms of endometriosis, pain.
From an endometriosis surgeon’s perspective, this type of classification does not focus on the fibrosis and deep involvement of the tissues and organs such as the bladder, bowels, diaphragm, and appendix lying behind the peritoneum. In short, outside of fertility, this classification system does little to describe the patient’s symptoms, which can include constipation, diarrhea, gas, bloating, bladder symptoms, painful sex, back pain, and leg pain. In this sense, endometriosis should be grouped as peritoneal endometriosis, ovarian endometriomas, and deep infiltrating endometriosis (DIE).
This section discusses peritoneal endometriosis. Particularly, how it should be defined based on the extension of the anatomy and the organs it affects across the abdominal lining.
Endometriosis is a disease that primarily involves the peritoneum. In other words, a majority of patients, particularly at a young age, who show symptoms of endometriosis, will have peritoneal endometriosis. This is regardless of the form of involvement or severity of the disease. It is, therefore, important to have a thorough understanding of what exactly this vital organ is.
Gray’s Anatomy recently accepted and classified the peritoneum and bowel mesentery as organs of their own. This new classification is a revolution because the peritoneum is no longer seen as just the lining of the abdominal cavity. It also has key immune functions and is responsible for a constant secretion of fluids. The drainage of these fluids to the hemidiaphragm and thoracic area may explain the distribution of endometriosis lesions in these regions.
Why is peritoneal endometriosis so unique?
Peritoneal endometriosis is unique in that it can vary from multifocal and multicentric involvement and from early angiogenesis to a full fibrotic nodule. This could be mild or diffuse. There may be one or two endometriosis lesions invading the peritoneum. Or, there could be as many as 50 lesions. Peritoneal endometriosis is the most common form of endometriosis in which lesions are typically non-pigmented rather than pigmented. This becomes particularly obvious after putting them in contrast and visualizing them with the aid of laparoscopic light.
What it stromal endometriosis?
Peritoneal lesions can also be cystic or fibrotic with peritoneal defects around central lesions, which will stain positive for stromal endometriosis. Stromal endometriosis is a concept unique to peritoneal endometriosis. It occurs when there are no glands but a visible stroma of the endometrium adjacent to the main pigmented or central lesion. This is called multi-focal endometriosis if it is in the same area but dispersed. It is called multi-centric if it involves multiple areas, even across the peritoneum.
What is “laterality” and how does it relate to a patient’s symptoms?
Interestingly, endometriosis lesions on the peritoneum mostly occur on the pelvic sidewalls. Deeper lesions are present on the uterosacral plate on each side (with more of a left side predominance over right) and cul-de-sac. The patient’s symptoms are thus justified when they talk about “laterality.”
This element of laterality is one of the most important caveats to a patient’s symptoms of pain, whether it is dysmenorrhea (painful menstruation), dyspareunia (painful sex), or dyschezia (painful bowel movements). This description can often coincide with the anatomical location of the endometriosis lesions themselves. In this sense, it is important for endometriosis specialists to look particularly at psoas muscles on each side. Here, there are nerves that travel above the muscle, which can often accumulate endometriosis lesions and be the site of the associated laterality of pain. This is also true for the hypogastric nerve, which surgeons often focus on in cases of the deep involvement of endometriosis of the presacral area, lateral to the rectum.
Where does peritoneal endometriosis occur?
When endometriosis is excised from the peritoneum, we are highly particular in defining and noting what anatomical area we removed the lesion from. We carefully define and note where endometriosis lesions are on the pelvic sidewall. This includes:
- the psoas muscle
- the pelvic rim
- the superior part of the ovarian fossa or ovarian cliff
- the periureteral ovarian fossa (where the ovaries typically rest)
- the uterosacral ligament
- the uterosacral plate
- the uteroarterial reflection
- the urethral bridge
- the posterior bold ligament
- the anterior and upper rectum
- the rectosigmoid colon
- The cul-de-sac
- rectovaginal cul-de-sac
- rectovaginal septum (underneath the peritoneum) and lateral extension above the pudendal nerve
- posterior cul-de-sac, which is behind the middle rectal artery and pararectal cul-de-sac
- anterior cul-de-sac including the uterovesical peritoneum (where the bladder and uterus meet) and the anterior and posterior portion of the bold ligament
- the sigmoid colon
- the appendix and periappendiceal region
What are pigmented vs. non-pigmented endometriosis lesions?
Peritoneal endometriosis is classified as pigmented or non-pigmented based on appearance. Pigmented endometriosis is the type that most doctors are familiar with. It fits the classical definition of endometriosis. The lesions are red, black, or a sort of “blueberry” color. The non-pigmented lesions can also be of typical appearance. Or they can be more subtle being white with a clear contour that can make them highly difficult to identify within the peritoneum.
How we identify non-pigmented endometriosis lesions
Non-pigmented endometriosis is only visible through techniques such as aqua blue contrast. This is because when we inject the contrast behind the peritoneum, it eliminates the reflection of overpowered light from the underlying red and white color that comes from the muscle tissue and other surrounding structures.
Diagnosis of peritoneal endometriosis
Peritoneal endometriosis is difficult to diagnose as it is not visible upon imaging examinations. Neither ultrasound technology nor the more thorough MRI exam, show signs of endometriosis involving the peritoneum. Laparoscopic visualization with excision surgery and an accompanying pathology report is the only way to formally diagnose peritoneal endometriosis. However, there are ways to assess for suspected peritoneal involvement upon physical examination. A pelvic exam, particularly accompanied by a rectovaginal assessment, can help an experienced gynecologist identify points of tenderness that can point to peritoneal endometriosis.
What is angiogenesis and how is it helpful in identifying early endometriosis?
One key identification point that indicates the development of early endometriosis is angiogenesis. Vascular changes and the formation of new, or enlarging capillary beds are always part of the inflammatory process. Usually, these changes migrate upward from deeper layers up to the surface of the peritoneum as new blood vessels form. This process of new blood vessel formation is called angiogenesis. The Aqua Blue™ inspection technique can easily identify different formations of angiogenesis. This includes elevations, spiral formation, and budding (also called sprouting). Increased vascularity along the new nerve formation might explain the unparalleled pain patients experience in case of early to late endometriosis.
Peritoneal endometriosis and its relationship with the immune system
Nearly all peritoneal endometriosis lesions excised have inflammation. This means that the body is resisting and fighting off the foreign glands and stroma of the anatomical dislocation of the endometrium. Thus, the immune system is attempting to reject these endometrial lesions. In fact, the most common sign and finding of excised lesions is this inflammation, which a pathologist will describe upon a biopsy report. It is not uncommon to see histiocytes, iron deposits, and infiltration of chronic inflammatory cells within the endometriosis lesions found in the peritoneum. These lesions can also have fibroblastic regeneration abilities. In addition, these lesions can often stain positive for stroma and estrogen receptors.
Thus, this is an area where stem cells and metaplasia can occur. All of this points toward a classic wound healing mechanism. However, the wounds being endometrial lesions, are never healing without surgical intervention. From this histological perspective, endometriosis is like a wound that never heals and flares up with menstruation and estrogen changes. Therefore, peritoneal endometriosis is where endometriosis is defined as not the traditional stroma gland of the endometrium, but more importantly by the lesions noted inflammation and scarring, which can explain a patient’s symptoms. It is thus important for a surgeon to clean these areas and remove lesions as fully as possible. This will ensure that a pathologist can clearly identify the lesions and define whether there are any abnormalities in the cell’s nuclei that could indicate cancerous changes. It will also allow the patient to receive a formal diagnosis of endometriosis.
Why do we feel non-pigmented endometriosis lesions are of particular importance?
Non-pigmented lesions are morphologically cystic in appearance, vesicular, and protruding into the peritoneum through small vegetations (abnormal growths). They can also microscopically infiltrate even deeper, affecting key nerves and other structures. This topic is thus of uttermost importance. This is because we feel that peritoneal endometriosis is the most ignored element in recognizing endometriosis. Many doctors do not recognize the importance of peritoneum involvement in endometriosis. Or they are not comfortable in addressing the issue due to its proximity to major vital organs. So the true removal of these lesions would necessitate vast surgical skill and experience on the part of the surgeon. But the main issue lies in recognizing the lesion itself and fully understanding the anatomy of the peritoneum and the surrounding organs.
Patients’ symptoms often correlate with the organs and peritoneal location that these non-pigmented endometriosis lesions are sitting within. If these lesions are sitting on the pelvic sidewall, patients usually experience back pain and leg pain during their periods. This is pain that follows the nerve path of the psoas region that innervates the vulva part of the thighs or the sciatic nerve in the back of the thigh. It is in the delicate removal of lesions from the peritoneum where the concept of excision surgery becomes important when treating patients. Many times both the endometriosis and abnormalities within the peritoneum may not reveal classical signs of pigmented endometriosis, even under a microscope.
This is why we rely on a combination of excision surgery with aqua blue contrast to treat our endometriosis patients. We believe each and every patient deserves the most meticulous care that we can provide.
How is our care in treating peritoneal endometriosis so unique?
We have experience in excising more than 20,000 peritoneum specimens. These include more lesions of non-pigmented nature and is key in ensuring our minimally invasive surgery is as thorough as possible. By utilizing our patented aqua blue contrast, we are able to identify and excise these lesions. We then ship them to a pathologist for a full biopsy report. In addition, following excision, we ensure reconstruction, repair, and restoration of the peritoneum anatomy in order to ensure organ function.
This is no easy feat. It is only possible thanks to decades of experience and a skilled team of specialists including GI and urology specialists on hand. We have found that peritoneal endometriosis is indeed present in nearly all patients with endometriosis. Thus we know and understand the importance of carefully operating in this area to ensure the highest chance for relief of symptoms for our patients.
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