If you’ve been told you have irritable bowel syndrome but your bowel symptoms are dramatically worse around your period — pain when you pass stool, diarrhoea in the days before menstruation, a bloated sensation that nothing shifts — there may be something else involved that your gastroenterology workup hasn’t yet considered.
Bowel endometriosis occurs when endometriosis tissue implants on or within the wall of the bowel, most commonly the rectosigmoid colon. It causes painful bowel movements (dyschezia), cyclical diarrhoea and constipation, rectal pressure, bloating, and sometimes cyclical rectal bleeding. These symptoms closely mimic irritable bowel syndrome but are distinguished by their consistent worsening around menstruation — a pattern that IBS does not follow. Bowel endometriosis requires specialist imaging and is frequently missed for years in people managed within gastroenterology alone.
Key Takeaways
- Bowel endometriosis most commonly affects the rectosigmoid junction — the area where the sigmoid colon meets the rectum — followed by the rectovaginal septum and, less often, the appendix or small bowel
- Dyschezia (painful defaecation) that worsens cyclically around menstruation is a recognised red-flag symptom for deep infiltrating endometriosis involving the posterior compartment
- Bowel symptoms that track the menstrual cycle are the most important clinical distinction from irritable bowel syndrome
- Standard colonoscopy and gastroenterology assessment frequently miss bowel endometriosis because most lesions do not penetrate the inner bowel lining (mucosa)
- Specialist transvaginal ultrasound and pelvic MRI with a deep infiltrating endometriosis protocol are the key non-surgical diagnostic tools
- Treatment ranges from hormonal suppression (which can significantly reduce symptoms) to surgical excision, including bowel resection in severe cases — decisions made in a multidisciplinary setting
Where Bowel Endometriosis Occurs
Endometriosis lesions can implant on the outer surface of the bowel (the serosa), invade into the muscular wall, or — in severe cases — penetrate through to the mucosal lining. The depth of infiltration influences both the severity of symptoms and the surgical complexity of treatment.
The most commonly affected sites, in order of frequency:
Rectosigmoid colon: The junction between the sigmoid colon and the rectum sits in the posterior pelvis, directly adjacent to the uterus and uterosacral ligaments — among the most common locations for deep infiltrating endometriosis overall. Lesions here cause the characteristic dyschezia, cyclical bowel changes, and rectal pressure that define bowel endo.
Rectovaginal septum: The thin fascial layer between the posterior vagina and the anterior rectum. Endometriosis in this location is dense fibrous disease that creates a nodule palpable on examination. It causes deep dyspareunia as well as bowel symptoms, because the affected tissue sits between two structures involved in both sexual function and defaecation.
Appendix: Appendiceal endometriosis is less common but worth noting — it can cause cyclical right iliac fossa pain that mimics appendicitis or, in some cases, causes genuine appendiceal complications.
Small bowel and caecum: Less common sites, but bowel endometriosis affecting the small intestine can cause more significant bowel obstruction-type symptoms.
Bowel Symptoms: What They Feel Like
Dyschezia (Painful Bowel Movements)
Dyschezia — pain during or immediately after defaecation — is one of the most specific symptoms of posterior compartment and bowel endometriosis. The pain is typically deep, cramping or sharp, located in the low pelvis or rectum. It may radiate to the sacrum or down the backs of the thighs.
The mechanism is straightforward: passing stool involves peristaltic contraction and tissue stretch in the posterior pelvis. When endometriosis lesions are present on or adjacent to the rectum, this mechanical stretch triggers pain through both direct tissue involvement and the neurological sensitisation that characterises deep infiltrating disease. Dyschezia that is significantly worse in the days before and during menstruation is a recognised indicator for gynaecological investigation.
Cyclical Diarrhoea and Constipation
Bowel habit changes in endometriosis tend to follow a predictable pattern tied to the menstrual cycle:
- Pre-menstrual diarrhoea: Many people experience loose stools, urgency, and cramping in the days immediately before menstruation, driven by prostaglandin release. In bowel endometriosis, this is often more severe and more prolonged than in people without endo involvement.
- Peri-menstrual alternation: Some experience constipation before menstruation followed by diarrhoea at its onset — a pattern driven by progesterone-related bowel slowing in the luteal phase, then prostaglandin-driven acceleration at period start.
- Intermenstrual near-normalisation: Bowel symptoms often improve significantly outside of the perimenstrual window — this recovery pattern is one of the strongest clinical markers of hormonally-driven bowel disease rather than primary bowel disorder.
Rectal Pressure and Incomplete Emptying
Lesions on the rectosigmoid or rectovaginal area can cause a constant or cyclically-worsening sense of rectal pressure — a feeling that the bowel needs to be emptied even after defaecation, or a heaviness in the posterior pelvis. This symptom is often distressing and difficult to describe in clinical appointments, but it is a recognised feature of significant posterior compartment disease.
Bloating
Pronounced abdominal bloating is extremely common in endometriosis, and bowel involvement amplifies it. Endo belly — severe cyclical bloating — involves multiple mechanisms including peritoneal inflammation, altered bowel motility, and pelvic oedema. When bowel endometriosis is also present, impaired bowel transit compounds the bloating further.
Cyclical Rectal Bleeding
This is the least common bowel symptom of endometriosis and indicates significant full-thickness bowel wall involvement — lesions that have penetrated through to the mucosal lining. Cyclical rectal bleeding specifically during menstruation (the bowel “menstruating” via the implants) is a relatively specific indicator. Any rectal bleeding warrants prompt medical assessment, both to evaluate for bowel endometriosis and to exclude other causes.
Why Bowel Endometriosis Is Misdiagnosed as IBS
The diagnostic overlap with irritable bowel syndrome is substantial and well-documented. Diarrhoea, constipation, bloating, cramping, and pelvic discomfort are core features of both conditions. IBS is common; endometriosis awareness in gastroenterology settings has historically been limited. The result is that many people with bowel endometriosis spend years under an IBS diagnosis without gynaecological investigation.
The key clinical features that should raise suspicion for endometriosis rather than — or in addition to — IBS:
- Cyclical pattern: Symptoms that reliably worsen in the 2–5 days before menstruation and during the period, then improve after it, are not typical of IBS. IBS symptoms are driven by food, stress, and bowel habit — not hormonal cycle.
- Dyschezia: Painful defaecation is not a recognised feature of IBS and should always prompt consideration of posterior compartment pathology.
- Dysmenorrhoea: Severe period pain alongside bowel symptoms is strongly associated with endometriosis, not IBS.
- Dyspareunia: Deep pain during sexual intercourse alongside bowel symptoms points to posterior compartment endometriosis.
- History of pelvic pain or known endometriosis: Any bowel symptoms in someone with established endometriosis warrant investigation for bowel involvement rather than attribution to a separate primary bowel condition.
“The rule of thumb is simple: if someone’s bowel symptoms are measurably worse around their period, IBS alone cannot explain that. The menstrual cycle should not significantly affect IBS. If it does, endometriosis is on the differential until excluded.”
If you are unsure whether your symptoms fit what endometriosis pain feels like, that article describes the full range of presentations including bowel and deep pelvic features.
Diagnosis
Why Standard Tests Miss It
Colonoscopy — the investigation most people expect bowel endometriosis to require — is usually normal in bowel endometriosis. Most lesions invade the bowel wall from the outside in, and the mucosal surface visible on colonoscopy is not involved until disease is very advanced. A normal colonoscopy does not exclude bowel endometriosis.
Standard pelvic ultrasound performed outside a specialist centre also frequently misses rectosigmoid involvement. The posterior pelvis requires specific technique — the bowel preparation protocol, systematic mapping of the rectosigmoid junction, and expertise in deep infiltrating endometriosis morphology — that a general gynaecology or obstetric ultrasound does not provide.
Specialist Imaging
Transvaginal ultrasound (TVUS) with a deep infiltrating endometriosis protocol is the first-line specialist investigation. In experienced hands at a dedicated endometriosis centre, TVUS has good accuracy for identifying rectosigmoid lesions. The sonographer systematically assesses the posterior cul-de-sac, rectovaginal septum, and rectosigmoid junction, and checks for “sliding sign” — the normal gliding movement between the rectum and posterior uterus, which is absent or reduced when endometriosis has created adhesions.
Pelvic MRI provides the most complete pre-surgical map of deep infiltrating disease, including bowel involvement. MRI can assess lesion depth, the length of bowel involved, and the distance from the anal sphincter — information that directly influences surgical planning. The request should specifically ask for a deep infiltrating endometriosis protocol; a standard pelvic MRI may not include the sequences and reporting detail needed.
Bowel MRI or MRI enema — in some specialist centres, an MRI with rectal gel distension is used to improve visualisation of lesion depth within the bowel wall.
Laparoscopy
Definitive diagnosis requires laparoscopy, where bowel lesions can be directly visualised, their extent assessed, and biopsies taken. This also provides the opportunity for treatment at the same time. If bowel resection is likely, a joint laparoscopy with both a specialist endo gynaecologist and a colorectal surgeon is the appropriate approach.
See our guide to how to get an endometriosis diagnosis for how to navigate referral to a specialist endometriosis centre if you are currently being managed in primary care or a non-specialist setting.
Treatment
Hormonal Suppression
Hormonal treatments — continuous combined oral contraceptive pill, progestogens, GnRH agonists — suppress oestrogen-driven disease activity and can produce significant improvement in bowel symptoms. Dyschezia, cyclical diarrhoea, and rectal pressure often respond well to hormonal suppression, though symptoms typically return when treatment is stopped.
For people whose bowel symptoms are manageable and who are not planning surgery, hormonal management is a reasonable first-line approach and can be maintained long-term. GnRH agonists provide the most complete hormonal suppression but are typically used with add-back oestrogen therapy to protect bone density in long-term use.
Surgical Excision
Surgery is considered when bowel symptoms significantly impair quality of life and do not respond to hormonal management, or when imaging suggests significant bowel wall infiltration that merits definitive treatment.
Surgical options for bowel endometriosis range in complexity:
- Shaving or disc excision: For lesions that do not penetrate deeply into the bowel wall — the nodule is shaved from the bowel surface or a disc of bowel wall is removed and repaired. Less complex, faster recovery.
- Segmental bowel resection: For lesions infiltrating deeply or involving a significant segment of bowel — the affected segment is resected and the bowel is re-joined (anastomosed). This is a more major procedure, performed jointly by an endometriosis surgeon and a colorectal surgeon at a specialist centre.
The decision between shaving, disc excision, and segmental resection depends on lesion size, depth, circumferential extent, and proximity to the anal sphincter. All options should be discussed as part of a multidisciplinary team including the patient’s reproductive goals, since some surgical approaches affect future fertility differently.
Post-operative bowel recovery requires time; temporary changes in bowel habit are common after bowel surgery and usually resolve within weeks to months.
Tracking Bowel Symptoms
Bowel symptoms are often difficult to describe accurately from memory in a clinical appointment. “I think my diarrhoea is worse around my period” is significantly less actionable than a three-month log showing diarrhoea consistently appearing on days −3 to +2 of the menstrual cycle, then resolving.
EndoTracking includes bowel symptoms — stool changes, dyschezia, bloating, rectal pressure — as trackable items alongside cycle phase and pain scores. Logging these consistently across two to three cycles builds a pattern document that makes the cyclical relationship visible and quantifiable — useful both for your own understanding and for specialist appointments.
See our endometriosis symptom tracker guide for how to get the most from cyclical symptom logging.
EndoTracking is a personal health tracking app and does not provide medical or gastroenterological advice. If you are experiencing bowel symptoms that worsen cyclically with your menstrual cycle, consult a gynaecologist with expertise in deep infiltrating endometriosis.