Colorectal endometriosis is the ectopic implantation of functional endometrial tissue in the colon or rectal wall, occurring in 5-12% of deep infiltrating endometriosis (DIE) cases. Rectosigmoid junction is most commonly affected (70-90%). Patients present with menstrual cycle-related pelvic pain, dyschezia (painful defecation), rectal bleeding, and diarrhea. Pelvic MRI is the gold standard for diagnosis and surgical planning. Lesions appear as hypointense solid nodular or plaque-like thickening on T2-weighted images — reflecting fibrotic stromal reaction and hemosiderin deposition. Transmural invasion depth determines treatment decision; surgical resection may be necessary in deep involvement (muscularis propria and beyond).
Age Range
20-50
Peak Age
35
Gender
Female predominant
Prevalence
Uncommon
Colorectal endometriosis begins with endometrial cells reaching the peritoneal cavity through retrograde menstruation and implanting on the bowel serosa. Implanted endometrial cells are estrogen-dependent and show proliferation and bleeding throughout the menstrual cycle — repeated microhemorrhage and inflammation each cycle triggers chronic fibrotic reaction. This fibrotic stroma forms dense desmoplastic reaction surrounding endometrial glands and causes hypointense appearance on T2-weighted MRI — the short T2 time results from dense collagen fibrils and hemosiderin deposition restricting water molecule mobility. The lesion progresses from serosa toward mucosa: serosa → muscularis propria → submucosa → mucosa. Muscularis propria involvement leads to wall thickening and luminal narrowing — appearing as concentric or eccentric wall thickening on CT and MRI. Repeated bleeding causes hemosiderin (iron deposition) accumulation creating T1 hyperintensity (methemoglobin/hemosiderin) and T2 hypointensity (T2-shortening effect of hemosiderin). Cyclic hemorrhages can form small endometriotic cysts (chocolate spots) within the bowel wall.
Mushroom cap-shaped T2 hypointense nodular thickening in the rectosigmoid wall — endometriotic implantation has progressed from serosa to muscularis propria taking the characteristic mushroom cap configuration. This morphology is characteristic of deep infiltrating endometriosis.
Hypointense nodular or plaque-like wall thickening in the rectosigmoid region on T2-weighted images. The lesion typically involves the serosa and muscularis propria layers. Hypointense signal reflects fibrotic stroma and hemosiderin deposition. Thickening may be eccentric (anterior wall predominant) or concentric. The mucosal layer is generally intact. Small T2 hyperintense foci near the lesion represent dilated endometrial glands.
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T2 hypointense nodular wall thickening in the rectosigmoid region is observed, consistent with deep infiltrating endometriosis; the lesion involves the serosa and muscularis propria layers.
Small hyperintense foci within the wall thickening on T1-weighted images — blood products (methemoglobin) within endometriotic cysts. This hyperintensity persists on fat-suppressed sequences (distinguishing from fat). T1 hyperintense foci are highly characteristic of endometriosis. Multiple hyperintense foci may be seen in larger lesions.
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T1 hyperintense foci within the wall thickening are observed, with persistent hyperintensity on fat-suppressed sequences consistent with blood products within endometriotic cysts.
Mild to moderate diffusion restriction in the solid endometriotic nodule on diffusion-weighted imaging. ADC values are lower than normal bowel wall but higher than malignant tumors. The dense cellular structure of the fibrotic component contributes to diffusion restriction.
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Mild diffusion restriction is observed in the endometriotic nodule on diffusion-weighted imaging with intermediate ADC values.
Eccentric or concentric wall thickening in the rectosigmoid region on portal venous phase CT. Thickening is of soft tissue density with moderate enhancement. Luminal narrowing may be present. Perirectal fat stranding or fine linear fibrotic bands may be visible. Associated ovarian endometrioma or uterosacral ligament thickening may accompany.
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Eccentric wall thickening in the rectosigmoid region with mild perirectal fat stranding on CT, with colorectal endometriosis to be considered in the differential diagnosis.
Hypoechoic nodular thickening in the rectosigmoid region on transvaginal ultrasound. The lesion originates from the muscularis propria and may contain echo-free or hypoechoic small cystic areas. Negative sliding sign (rectum does not slide against posterior uterine wall) suggests adhesion and deep infiltration. TVUS has high sensitivity for diagnosis in experienced hands.
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Hypoechoic nodular wall thickening in the rectosigmoid region with negative sliding sign on transvaginal ultrasound, consistent with deep infiltrating endometriosis.
Persistent hyperintense foci in the lesion on T1-weighted fat-suppressed sequences — confirming blood products and distinguishing from fat content. This sequence specifically demonstrates hemoglobin degradation (methemoglobin) within endometriotic cysts. Persistent T1 hyperintensity after fat suppression is pathognomonic for endometriosis.
Report Sentence
Persistent hyperintense foci in the lesion on T1 fat-suppressed sequence consistent with blood products within endometriotic cysts, supporting the diagnosis of endometriosis.
Criteria
Most common form (70-90%). Located at the rectosigmoid junction or upper rectum. Frequent association with Douglas cul-de-sac obliteration.
Distinct Features
Anterior wall predominance, eccentric thickening, dyschezia and cyclic rectal bleeding. Lesion-to-anal verge distance is critical for surgical planning (>8 cm anterior resection, <8 cm low anterior resection required).
Criteria
Cecum or terminal ileum involvement. Accounts for 5-10% of all colorectal endometriosis cases. May be confused with appendicitis or Crohn disease.
Distinct Features
Right lower quadrant pain, cyclic symptoms. Cecal/terminal ileum wall thickening on CT. T2 hypointense thickening with T1 hyperintense foci on MRI. Menstrual history is critical in differential diagnosis.
Criteria
Involvement of more than one bowel segment. Seen in severe endometriosis cases. Usually rectosigmoid + ileocecal or rectosigmoid + sigmoid colon.
Distinct Features
T2 hypointense thickening in multiple bowel segments. With Douglas obliteration, ovarian endometrioma, and uterosacral ligament involvement on pelvic MRI. Requires multidisciplinary surgical planning.
Distinguishing Feature
Adenocarcinoma shows heterogeneous intermediate signal on T2 while endometriosis is markedly T2 hypointense. In adenocarcinoma, the mucosal surface is usually disrupted/ulcerated; in endometriosis, the mucosa is typically intact. Lymphadenopathy and distant metastasis may accompany adenocarcinoma.
Distinguishing Feature
Crohn disease shows T2 hyperintense active inflammation or T2 hypointense fibrotic stenosis; endometriosis is homogeneously T2 hypointense. Skip lesions, fistula, and mesenteric fatty proliferation (creeping fat) are characteristic of Crohn; absent in endometriosis. Menstrual cycle relationship suggests endometriosis.
Distinguishing Feature
GIST shows heterogeneous T2 hyperintense signal while endometriosis is T2 hypointense. GIST shows exophytic growth pattern; endometriosis infiltrates from serosa toward mucosa. T1 hyperintense foci are not seen in GIST (except hemorrhagic GIST).
Distinguishing Feature
Lymphoma shows intermediate T2 signal with homogeneous enhancement; endometriosis is T2 hypointense. Aneurysmal dilation (luminal widening) may be seen in lymphoma; luminal narrowing is typical in endometriosis. Systemic B symptoms and widespread lymphadenopathy may accompany lymphoma.
Urgency
routineManagement
surgicalBiopsy
Not NeededFollow-up
6-monthTreatment of colorectal endometriosis depends on symptom severity and invasion depth. Hormonal therapy (OCP, progestins, GnRH analogs) provides symptom control in mild cases. Surgical resection is recommended for deep infiltration (muscularis propria and beyond) — shaving, disc excision, or segmental resection. Pelvic MRI is essential in surgical planning to determine transmural invasion depth and number/location of lesions. Multidisciplinary team approach (gynecologist, colorectal surgeon, radiologist) is important. Malignant transformation is extremely rare but has been reported.
Medical treatment (hormonal) or surgical resection is applied. Deep infiltrative endometriosis (DIE) is evaluated by MRI for surgical planning. Malignant transformation is very rare.