Appendiceal endometriosis is a rare form of extrapelvic endometriosis characterized by ectopic implantation of functional endometrial tissue (glandular epithelium and stroma) in the appendix. Appendiceal involvement is seen in 3-18% of gastrointestinal endometriosis cases. Endometrial tissue can invade from the appendiceal serosa toward the mucosa, and under cyclical hormonal influence, can lead to hemorrhage, fibrosis, and mass formation. Clinically, it can mimic appendicitis, Crohn's disease, or appendiceal neoplasm.
Age Range
20-50
Peak Age
35
Gender
Female predominant
Prevalence
Rare
Appendiceal endometriosis begins when endometrial cells shed into the pelvic cavity via retrograde menstruation (Sampson's theory) are transported to the right lower quadrant through peritoneal fluid circulation and implant on the appendiceal serosa. The implanted endometrial glandular epithelium and stroma respond to ovarian estrogen and progesterone, exhibiting cyclical changes — proliferation, secretion, and decidualization. During the menstrual bleeding phase, ectopic endometrial tissue also bleeds; these recurrent microhemorrhages lead to hemosiderin deposition, chronic inflammation, and reactive fibrosis. Fibrotic reaction causes wall thickening and luminal narrowing of the appendix — this appears as wall thickening on CT and MRI. Hemosiderin deposition is reflected on MRI as T1 high signal and T2 low signal (shading effect). In advanced stages, transmural invasion can lead to complete obstruction of the appendiceal lumen and secondary appendicitis.
The combination of high signal on T1 (blood products — methemoglobin) and low signal on T2 (hemosiderin deposition — shading effect) in the appendiceal wall lesion is considered pathognomonic for endometriosis. Signal persistence on fat-suppressed T1 excludes fat-containing lesions.
Focal lesion with high signal intensity on T1-weighted sequences in the appendiceal wall or serosa. High signal results from blood products such as methemoglobin and hemosiderin within the endometriotic implant. Signal persistence on fat-suppressed T1 (non-fat T1 hyperintensity) is critical for endometriosis diagnosis.
Report Sentence
A focal lesion with high signal intensity in the appendiceal wall is observed on T1-weighted sequences, with signal persistence on fat suppression compatible with endometriosis.
Low signal (shading effect) in the area of endometriotic implant on T2-weighted sequences. Hemosiderin accumulated from chronic recurrent hemorrhage and dense protein content cause T2 shortening. Fibrotic reaction around the lesion also contributes to low T2 signal.
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Low signal (shading effect) is observed in the lesion within the appendiceal wall on T2-weighted sequences, compatible with chronic endometriotic implant.
Focal or segmental thickening of the appendiceal wall on CT. The thickened wall segment may show enhancement. Periappendiceal fat stranding may accompany due to chronic inflammation. CT findings are non-specific and may be indistinguishable from appendicitis or neoplasm.
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Focal thickening and mild enhancement of the appendiceal wall is observed; further evaluation with MRI is recommended for endometriosis in the clinical context.
Hypoechoic nodular thickening in the appendiceal wall or serosa on ultrasonography. Lesion may have irregular margins. Internal echogenic foci (hemosiderin) may be seen. Pelvic endometriosis findings (endometrioma, Douglas obliteration) should be concurrently assessed.
Report Sentence
Hypoechoic nodular thickening is observed in the appendiceal wall; appendiceal endometriosis should be considered in the context of pelvic endometriosis.
Enhancing nodular lesion in the appendiceal serosa or wall on contrast-enhanced MRI. Fibrotic component shows late enhancement while active endometrial tissue may show early enhancement. When evaluated together with low T2 signal of surrounding fibrotic tissue, supports endometriosis.
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An enhancing nodular lesion in the appendiceal serosa is observed on contrast-enhanced MRI, compatible with endometriosis in conjunction with T1 hyperintensity and T2 shading effect.
Criteria
Endometrial implant is confined to the appendiceal serosa; no invasion into muscularis propria.
Distinct Features
Small nodule on serosal surface on MRI, lumen preserved, no obstruction. Generally asymptomatic or mild cyclical pain.
Criteria
Endometrial implant involves the muscularis propria and submucosa. Luminal narrowing or obstruction may be present.
Distinct Features
Marked wall thickening, luminal narrowing, risk of secondary appendicitis. Larger T1 hyperintense mass on MRI. May require surgical treatment.
Distinguishing Feature
LAMN shows low T1 signal, high T2 signal (mucinous content), and mural calcification. Endometriosis shows high T1 signal (blood products) and low T2 signal (shading).
Distinguishing Feature
Mucocele shows thin-walled cystic dilatation, low T1 and high T2 signal. Endometriosis shows nodular wall thickening, high T1 and low T2 signal.
Distinguishing Feature
Lymphoid hyperplasia shows homogeneous intermediate signal, no T1 hyperintensity. Endometriosis shows T1 hyperintensity and T2 shading.
Urgency
routineManagement
surgicalBiopsy
Not NeededFollow-up
specialist-referralAppendiceal endometriosis is generally detected incidentally during pelvic endometriosis surgery or appendectomy performed for suspected appendicitis. In symptomatic patients (cyclical right lower quadrant pain, obstructive symptoms), laparoscopic appendectomy is curative. Isolated appendiceal endometriosis is rare and usually accompanies pelvic endometriosis — therefore gynecological evaluation and pelvic MRI are recommended. Hormonal therapy (GnRH agonists, oral contraceptives) can be considered as a medical option. Malignancy risk is low, but clear cell carcinoma or endometrioid carcinoma can rarely develop in the setting of endometriosis.
Appendiceal endometriosis is usually treated with appendectomy. The appendix should be evaluated during surgery in pelvic endometriosis cases. Malignant transformation is very rare but endometrioid carcinoma may develop. Hormonal therapy (GnRH agonists) can provide symptom control but surgery is definitive treatment.