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Diagnosing Bowel Endometriosis: Step-by-Step Workup

Given the potential for so many diagnostic wrong turns, we’ve included in this next section a step-by-step guideline so that you can be aware of the diagnostic process and gain insight into how and why diagnostic errors can occur.

STEP 1 – Clinical Evaluation & Consultation

Best medicine in the world? Listening to the patient.

The first step in a diagnostic workup is to schedule ample time for your initial consultation, so that you have a chance to discuss in detail the symptoms you’ve been experiencing, as well as review your past medical history and family medical history if available.

Dr. Nezhat will also ask specific questions to determine if you have additional risk factors for endometriosis of the gastrointestinal tract (bowel), which you may recall includes a previous diagnosis of endometriosis, previous surgeries for endometriosis, previously diagnosed advanced stage disease, and/or the presence of ovarian involvement or deeply infiltrating nodules.

Another aspect that Dr. Nezhat always keeps in mind is the possibility of post-menopausal endometriosis, which can occur more often than most realize. For example, one study suggests that up to 7% of bowel endometriosis cases have occurred in post-menopausal women. In some reports, the patient had no endometriosis symptoms in years, but experienced new or a recurrence of old symptoms after menopause, during which time the patient began taking hormonal replacement therapies, whichlikely re-triggered the aberrant growths.

STEP 2 – Pelvic & Physical Exam

For extra details on what to expect during a pelvic exam for endometriosis, you can click here to visit that specific section of our website.

As for suspected cases of bowel endometriosis, the pelvic exam protocols are essentially the same, especially for specialists, who know that bowel involvement is a lot more common than the old medical literature suggests and therefore always look for signs of this form of the disease as part of a normal diagnostic work-up.

As with all forms of endometriosis, the only way to definitively diagnose bowel endometriosis is through surgical biopsy. However, before taking this invasive step, a pelvic exam can help specialists discern by palpation signs of disease suggestive of bowel involvement. When endometriosis has involved the rectum, among the most common findings during a pelvic exam include the presence of painful nodules and/or tenderness in the rectovaginal cul-de-sac (Pouch of Douglas), and on the uterosacral ligaments. Vaginal and uterine pain may also be present.

Bi-digital evaluations can be especially helpful in determining the extent to which the rectum is involved, especially in severe cases, such as those with obliterated cul-de-sac, where the anterior (front) rectal wall has adhered to the posterior (back) of the uterus, the cul-de-sac, and in some cases the posterior wall of the vagina as well. Studies have shown that patients with an obliterated cul-de-sac are three times more likely to have bowel endometriosis than women without this particular manifestation. Therefore, even at this early diagnostic stage, specialists can gather a lot of information that can help them narrow the diagnosis and determine if someone is a candidate for further surgical evaluation.

With the help of a speculum or hysteroscope, deeply infiltrating nodules that have grown from the rectal wall into the back of the vaginal canal may also be visualized and therefore suggestive of bowel involvement.

Considering that endometriosis is a whole-body disease, Dr. Nezhat also takes time to evaluate your overall physical health, since endometriosis may adversely affect your body in many different ways.

STEP 3 – Imaging Tests & Procedures

As mentioned in other sections, unfortunately even the most advanced imaging technologies have proven to be of limited value for diagnosing endometriosis. While bulky disease may appear in imaging tests, the more common flat, superficial lesions and adhesions tend to be less discernible. Colonoscopies have particularly high fail rates in detecting bowel endometriosis, since most of the growths occur on the outside of the bowel, rather than inside of it.
However, specialists have more training in evaluating imaging tests and therefore may uncover important findings that are suggestive of bowel involvement or which at least may help rule out other conditions. From our experience, the most useful imaging techniques are transvaginal ultrasound (TVUS) and transrectal ultrasound (TRUS), combined with double contrast barium enema (DCBE).

Under expert analysis, these imaging tests may help document the extent of disease, including the location, number, and shape of nodules or growths, all of which can facilitate pre-operative planning and patient counseling regarding potential surgical benefits and risks. Details of each imaging technology are listed below.

Transvaginal Ultrasound
Transvaginal ultrasound (also called sonography) uses sound waves to help detect masses and anatomical details in a (relatively) non-invasive manner. However, like pelvic exams, we know that ultrasound evaluations can also be painful for women with endometriosis, and so we work with patients to minimize any discomfort as much as possible during this step as well.

If bowel endometriosis is suspected, a double contrast barium enema (DCBE) can be included, which may help improve the ultrasound’s ability to detect aberrant growths or anatomical distortions suggestive of disease. Some have allergies to barium, so this step can be excluded if necessary. Color Doppler ultrasound is also included, which is especially useful for detecting vascularization patterns. This can help distinguish between different conditions, such as adenomyosis and fibroids, while excessive vascularization in masses may be a red flag for cancer.

As for the reliability of ultrasound in detecting signs of bowel endometriosis, studies vary, but one recent meta-analysis of pooled estimates found that transvaginal ultrasound had a sensitivity of 91% and specificity of 98%. This included deeply infiltrating endometriosis of the rectosigmoid.

However, other studies have shown lower results and the predictive value is highly dependent on the experience of those interpreting the results. Transvaginal ultrasound also can’t reach the entire bowel, and so other imaging tests may be necessary to complete a pre-operative diagnostic analysis.

Ultrasound Images
From a specialist’s perspective, the black, white, and gray images that ultrasound produces can actually reveal quite a bit about the inside of the body. On ultrasound, bowel endometriosis can appear as an irregularly-shaped mass or lesion, with hypoechoic features (no echo), which appear black on the image.

The mass may be sitting on top of and/or penetrating the bowel wall. Depth of invasion into the bowel wall generally cannot be determined with any reliable accuracy.  Bowel endometriosismay also cause thickening to certain parts of the bowel wall (hypertrophy), particularly to the muscularispropria, a muscular lining located in about the middle of the bowel wall, the third layer from the top. A bowel wall thickness greater than about 3 millimeters (mm) is considered abnormal and may be visible on ultrasound. (Click here for a good image showing the various layers of the bowel). Fibrosis and adhesions are common with bowel endometriosis as well, and may give a hypoechoic tethering appearance.

Appearance of Bowel Endometriosis at Transvaginal Ultrasound:
* A hypo-echoic and irregularly-shaped mass/es adhered to outside of bowel wall
* Some spiculation (spiked edges) may be present
* In penetrating masses, thickening of the muscularispropria> 3 mm
* Adhesions may appear as thin hypo-echoic bands that fan out from the mass
* Stenosis (narrowing) of bowel lumen due to wall hypertrophy or mass bulging into lumen
* Mucosa layer may appear serrated (wavy outline) in more invasive disease

Transrectal Ultrasound
Transrectal ultrasound (TRUS) can help further evaluate the extent of disease, including nodule size and which layers of the bowel wall appear to have involvement with endometriosis.  However, it is not possible to exam the upper part of the colon beyond the rectosigmoid junction. Reliability of TRUS is similar to the TVUS, with various studies reporting a range of 88-96% for sensitivity and 80-100% for specificity, respectively.

Magnetic resonance imaging (MRI) is another imaging technology that can be used to help visualize those parts of the bowel that TVUS and TRUS cannot reach. Sensitivity can be high, from 77-93%. . However, some studies suggest that MRI is less reliable than ultrasound. With T1-weighted MRI, bright images (hyperintense) can be suggestive of bowel endometriosis.

Colonoscopy Fails
As mentioned, colonoscopy is a very poor tool for diagnosing bowel endometriosis. This is because a colonoscopy looks on the inside of your bowel. However, the majority of bowel endometriosis growths occur on the outside of the bowel and only rarely penetrates beyond the bowel’s mucus layer (inner layer).

In a small percentage of cases, there may be ulcer-like discoloration or what appears to be swelling (edema) or inflammation of the inner lining that an experienced colonoscopist may be able to detect. A narrowing of the bowel lumen (stenosis) or bulging may also be visible, as would those cases when endometriosis actually does infiltrate through the full thickness of the bowel. However, the vast majority of endometriotic growths of the bowel cases cannot be detected with colonoscopy and both the visual and biopsy tests will come back as normal..


Lab tests have a limited role in the diagnosis of endometriosis, but may be useful for ruling out other conditions and can provide an overall picture of your health in general. For example, women with endometriosis may develop anemia, and so your doctor should always check for this condition, as it can cause severe fatigue, depression, and other troublesome symptoms.

As for specific serum biomarkers, unfortunately researchers are still searching for one. For now, some have proposed using the cancer antigen called CA-125 as a biomarker, but most studies have shown it to be highly unreliable for diagnosing endometriosis.

For ruling out other conditions that mimic bowel endometriosis, there are some tests that may be helpful. For example, there are two specific blood tests to check for antibodies associated with celiac disease. Lactose, fructose, and gluten intolerance tests can also be done to rule out food intolerances that may cause GI symptoms.

Ruling out IBS can be difficult for non-specialists, especially since IBS can flare up during menstruation, which may be one of the main reasons why so many women with bowel endometriosis are incorrectly diagnosed with IBS. While there is no specific test to rule out IBS, a careful review of clinical signs and imaging tests can help narrow the analysis. See the below table for a side-by-side comparison of IBS and bowel endometriosis symptoms.

IBS (Irritable Bowel Syndrome)
Chronic but moderate abdominal pain more common
Chronic, severe abdominal pain more common
Early satiety more common
Menstrual irregularities more common
Eating-associated nausea much more common
Menstruation-associated nausea much more common
Upper abdomen symptoms more common
Lower abdominal pain symptoms more common
GERD (acid reflux) symptoms more common
Pain with sexual intercourse much more common
If menstruation increases symptoms, changes in bowel habits more common than extreme pain
If menstruation increases symptoms, extreme pain is more likely to be reported
If rectal bleeding, blood is likely bright red indicating that hemorrhoids or tears most likely cause
If rectal bleeding, blood more likely to be darker in color and more likely to be associated with menstruation
More likely to have some relief of symptoms with dietary changes
Dietary changes may help some, but less likely to relieve extreme pain symptoms
More likely to have symptom stability with few signs of progression
Progression of symptoms more likely, meaning symptoms get worse over time
Vaginal pain much more common
Rectal pain more commonly reported
Extreme pain during bowel movement significantly more common
Extreme pain with vaginal or rectovaginal pelvic exam more common
Pain with sitting more common
Pain symptoms in extremities or other non-abdominal parts of the body – like the hips, lower back, and legs – more likely to be reported
Past history of infertility and/or sub-fertility
Past history of multiple miscarriages, including ectopic pregnancies


IBS or Bowel Endometriosis

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