Bladder endometriosis is the ectopic presence of functional endometrial tissue within the bladder wall. It is part of the deep infiltrative endometriosis (DIE) spectrum and accounts for 1-2% of all endometriosis cases. It most commonly involves the bladder dome and posterosuperior wall — the region closest to the vesicouterine pouch (anterior cul-de-sac). Ectopic endometrial tissue responds to the menstrual cycle: bleeding, edema, and inflammation occur during menstrual periods. This cyclic activity forms the basis of T1-hyperintense hemorrhagic foci on imaging. Clinically presents with cyclic hematuria (during menstruation), dysuria, pelvic pain, and urinary frequency. Diagnosis is often delayed (average 7-10 years) because symptoms are nonspecific. MRI is the most sensitive and specific imaging modality for bladder endometriosis diagnosis — T1-hyperintense hemorrhagic foci are pathognomonic.
Age Range
25-50
Peak Age
35
Gender
Female predominant
Prevalence
Uncommon
The pathophysiology of bladder endometriosis is explained by a combination of retrograde menstruation theory (Sampson) and metaplasia/coelomic theory. In retrograde menstruation, endometrial cells pass through fallopian tubes into the peritoneal cavity, implant in the vesicouterine pouch, and infiltrate through the bladder serosa into the wall. Ectopic endometrial tissue responds to estrogen and progesterone produced by the ovaries — showing growth in the proliferative phase, secretion in the secretory phase, and bleeding in the menstrual phase. Recurrent micro-hemorrhage with each menstrual cycle leads to hemosiderin accumulation and chronic inflammatory response. Hemosiderin (iron storage product) has paramagnetic properties and causes T1 shortening on MRI — this is the basis for the characteristic hyperintense signal on T1-weighted images. Chronic inflammation and fibrosis cause nodular thickening of the bladder wall — appearing as a focal mass on CT and MRI. On T2-weighted images, the fibrotic component shows hypointense signal while hemorrhagic foci show variable T2 signal (depending on hemoglobin degradation stage).
Presence of hyperintense foci maintained with fat-sat on T1-weighted images in a focal lesion of the bladder wall is nearly pathognomonic for endometriosis. This finding reflects hemosiderin and methemoglobin accumulation from cyclic menstrual bleeding of ectopic endometrial tissue. No other bladder pathology (urothelial carcinoma, leiomyoma, paraganglioma) shows this specific T1 signal characteristic with similar frequency. Correlation with cyclic symptoms (hematuria worsening with menstruation) confirms the diagnosis.
Hyperintense foci within the endometriosis nodule in the bladder wall on T1-weighted images — T1 shortening due to hemorrhagic content and hemosiderin accumulation. Signal is maintained on fat-sat T1 sequences (confirming blood product, not fat). Hyperintense foci may be scattered or multifocal within the nodule. This finding is nearly pathognomonic for endometriosis and distinguishing from other bladder pathologies.
Report Sentence
Hyperintense foci within the nodular thickening of the posterosuperior bladder wall on T1-weighted images with maintained signal on fat-sat T1; consistent with hemorrhagic endometriosis implant.
Scattered hyperintense foci within a predominantly hypointense nodular structure in the bladder wall on T2-weighted images. Hypointense stroma represents fibrosis and smooth muscle hyperplasia, while hyperintense foci represent ectopic endometrial glands and hemorrhagic cystic areas. This 'bright spots on dark background' appearance (shading sign) is characteristic of endometriosis. Nodule size is generally between 1-4 cm. Bladder mucosa is usually intact.
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Nodular structure with hyperintense foci within predominantly hypointense stroma is observed in the bladder wall on T2-weighted images; consistent with endometriosis implant.
Mild to moderate diffusion restriction may be observed in the solid component of the endometriosis nodule on DWI. ADC values are generally moderate (1.0-1.5 × 10⁻³ mm²/s). Prominent diffusion restriction is not expected — an important finding for differentiation from malignant tumors. Hemorrhagic components may produce false high signal on DWI due to T2 shine-through effect; ADC verification is required.
Report Sentence
Mild diffusion restriction is observed in the endometriosis nodule on DWI with moderate ADC values; no malignant-level diffusion restriction identified.
Moderate homogeneous or heterogeneous enhancement of the endometriosis nodule on contrast-enhanced MRI. Enhancement reflects vascularity within the fibrotic stroma and vascular supply of ectopic endometrial tissue. Degree of enhancement may vary with menstrual cycle phase — more prominent in proliferative phase. Fat-sat T1 post-contrast sequences best evaluate enhancement.
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Moderate enhancement of the nodular structure in the bladder wall is observed on contrast-enhanced images.
Focal nodular thickening of the posterosuperior bladder wall on CT — soft tissue density mass (30-60 HU) with moderate enhancement. Calcification is rare. CT findings are nonspecific and cannot reliably differentiate from urothelial carcinoma — MRI is superior. However, CT may show accompanying pelvic endometriosis findings (endometrioma, uterosacral thickening).
Report Sentence
Focal nodular thickening of the posterosuperior bladder wall is observed on CT; MRI is recommended for differentiation between endometriosis and neoplasia.
Hypoechoic nodular structure in the posterosuperior bladder wall on transvaginal US — small anechoic cystic foci (ectopic endometrial glands) may be seen within. Nodule margins may be well-defined or irregular. Minimal vascularity may be seen on Doppler. US sensitivity is lower than MRI but may be incidentally detected during pelvic US. Increase in nodule size and cystic components may be observed during menstruation (cyclic change).
Report Sentence
Hypoechoic nodular structure with small cystic foci in the posterosuperior bladder wall on transvaginal ultrasonography, which may be consistent with endometriosis; MRI confirmation is recommended.
Criteria
Endometrial implant confined to bladder serosa, not invading muscularis propria.
Distinct Features
Difficult to detect on imaging — may appear as thin peritoneal nodule. Laparoscopic diagnosis is superior.
Criteria
Endometrial implant invading muscularis propria. Nodular thickening ≥5 mm. Most commonly diagnosed form.
Distinct Features
Prominent nodular thickening on MRI, T1-hyperintense hemorrhagic foci, T2-hypointense stroma. Submucosal mass or bluish lesion on cystoscopy.
Criteria
Multiple DIE foci accompanying bladder involvement — uterosacral ligament, rectovaginal septum, ovarian endometrioma.
Distinct Features
MRI pelvis protocol should scan all compartments. Endometrioma (T1-hyperintense ovarian cyst) frequently accompanies. Mapping of all DIE foci required for surgical planning.
Distinguishing Feature
Urothelial carcinoma does not show T1-hyperintense hemorrhagic foci and demonstrates prominent diffusion restriction (ADC <0.8). In endometriosis, T1-hyperintense foci are pathognomonic and diffusion restriction is mild. Urothelial carcinoma usually in older patients associated with smoking history.
Distinguishing Feature
Leiomyoma appears as homogeneously T2-hypointense solid mass; no hemorrhagic foci or T1 hyperintensity. Endometriosis has T1-hyperintense hemorrhagic foci within T2-hypointense stroma. Cyclic symptom variation not expected in leiomyoma.
Distinguishing Feature
Urachal carcinoma appears as midline calcified mass at bladder dome; endometriosis is non-calcified nodule at posterosuperior wall. Urachal carcinoma has mucinous component and Retzius space extension; in endometriosis, T1-hyperintense hemorrhagic foci and cyclic symptoms are distinguishing.
Distinguishing Feature
Metastasis in setting of known primary malignancy shows prominent diffusion restriction and aggressive enhancement. In endometriosis, T1-hyperintense foci and mild diffusion restriction are distinguishing. No cyclic symptom variation in metastasis.
Urgency
routineManagement
medicalBiopsy
Not NeededFollow-up
6-monthTreatment of bladder endometriosis depends on symptom severity and fertility desire. Medical therapy uses GnRH agonists (leuprolide), progestins (dienogest), and combined oral contraceptives — controls symptoms but does not eliminate the lesion. Surgical treatment may include laparoscopic partial cystectomy or transurethral resection (TUR). Partial cystectomy preferred for deep infiltrative lesions. Recurrence rate is approximately 5-15%. MRI follow-up recommended — lesion size, symptom correlation, and malignant transformation monitoring.
Bladder endometriosis can clinically mimic bladder carcinoma. MRI is the gold standard — T1 high signal is pathognomonic. Cyclic hematuria (catamenial hematuria) is an important clinical clue. Treatment is surgical excision (partial cystectomy or transurethral resection) and/or hormonal therapy (GnRH agonists). Cystoscopy typically shows bluish-purple submucosal nodule. Malignant transformation is very rare.