Appendiceal endometriosis: Case report of a rare differential diagnosis of acute appendicitis

Lucía Aragone: study concept, writing the paper, data collection, analysis and interpretation. Mariana Toffolo Pasquini: data collection and analysis. Victoria Scasso Rebzda: data collection and analysis. Matías Mihura: data collection and analysis. Mariela Sol Talarico: data collection.

Written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal on request.

Ethical approval is exempt at our institution.

We have received no funding from any organizations for this work.

Lucía Aragone

In this case we report appendiceal endometriosis as a rare differential diagnosis of acute appendicitis. This entity should always be considered among young women of childbearing age presenting with right lower quadrant abdominal pain. Definitive diagnosis is only confirmed after histopathological examination. Although appendectomy relieves the acute symptoms, gynecological follow up is strongly recommended.

Endometriosis is an estrogen-dependent, chronic inflammatory disorder with characteristic presence of viable endometrial tissue outside the uterine cavity. Intestinal involvement may occur in 3–34 % of females with endometriosis; however, the sigmoid colon and rectum are most commonly affected [7] . Appendiceal endometriosis is rare. In 1951, Collins et al. reported 150 cases of appendiceal endometriosis [8] . Afterwards Collins further studied over 50,000 random pathologic assessments of the appendix and reported a prevalence of appendiceal endometriosis as 0.054 % [9] . More recent studies, however, have reported a prevalence of appendiceal endometriosis around 1 to 2.8 % [1] , [5] . Symptomatic endometriosis of the appendix is highly variable in presentation and may mimic acute appendicitis or may have other symptoms such as abdominal colic, nausea or even melena. Commonly these symptoms appear along with menstruation. [7] , [10] In our patient, the symptoms were concerning acute appendicitis, but they appeared along with her menstrual period. Complications of appendiceal endometriosis are rare, but include cecal intussusception, gastrointestinal perforation and lower gastrointestinal bleeding. [3] , [11] Ultrasound, CT-Scan and laparoscopy can be useful for evaluation although definitive diagnosis is obtained with the histopathological study. Findings of hemorrhagic peritoneal fluid and nodularity of the appendix or other intraperitoneal organs may be an indicator of the presence of endometriosis during surgery. Yet, in some cases appendiceal endometriosis can be confined only to the appendix. In our patient, we found the thickened appendix along with multiple peritoneal implants of endometriosis in the rectum, sigmoid colon, ovaries and fallopian tubes during laparoscopy. The histopathological result of endometrial tissue in the appendix confirmed the diagnosis of appendiceal endometriosis. Differential diagnoses of appendicular mass should be considered, such as neuroendocrine tumors, which are the most common neoplasms of the appendix [12] . These can appear more frequently in woman and can be seen on CT-scans as small round masses confined to the distal appendix, similarly to our patient's CT-scan [13] . Differentiating these conditions can be highly challenging and preoperative diagnosis of appendiceal endometriosis is not common. Post-operatively, our patient's pain subsided after appendectomy, suggesting that the appendiceal endometrial deposits were the cause for symptoms. Acute symptoms usually resolve after appendectomy even though lower abdominal pain has been known to recur. [14] , [15] This is probably due to associated pelvic endometriosis [16] . Ongoing pain despite appendectomy warrants investigation for other abdominopelvic endometrial deposits or non-gynecological diagnosis. Gynecological assessment for medical treatment and follow-up after surgery is highly recommended. Our patient remained stable, with no further symptoms, pain or other morbidities a year after the surgery.

Endometriosis is defined as the presence of endometrial glands and stroma abnormally implanted in locations other than the uterine cavity [1] , [2] . Up to 6–10 % of the general female population may be affected by this condition [3] . The symptomatology of the disease is often related to the location of the lesions. Although acute appendicitis is the most common surgical pathology responsible for right lower quadrant abdominal pain [4] , appendiceal endometriosis is an exceedingly rare presentation of extragonadal endometriosis. Endometriosis commonly affects women of childbearing age with a wide spectrum of clinical manifestations. Women can present with symptoms mimicking acute appendicitis or other entities [5] . We describe a case of appendiceal endometriosis presenting with acute right lower quadrant abdominal pain and we discuss appendiceal endometriosis as a rare differential diagnosis of acute appendicitis in women of childbearing age. We report this case according to the Updating Consensus Surgical CAse REport (SCARE) 2020 guidelines [6] .

A 39-year-old lady, without any significant past medical or surgical comorbidities, presented with one week history of abdominal pain, localized the lower right quadrant. There were no other gastrointestinal, gynecological or urinary tract symptoms. The symptoms started along with her menstrual period. Upon examination, she presented with right lower quadrant abdominal pain, without guarding or rebound tenderness. White blood cell count was normal, without other pathological laboratory findings. An abdominal ultrasound was done, showing a dilated appendix in the right lower quadrant of 7,5 mm of diameter, associated with fat stranding and localized free fluid ( Fig. 1 ). Due to diagnostic doubts, a CT-scan was done, demonstrating a thickened appendix, measuring 13 mm of diameter, suggestive of appendicitis ( Fig. 2 ). Fig. 1 Abdominal ultrasound showing the thickened appendix of 7,5 mm of diameter in the right lower quadrant (white arrow), associated to fat stranding and free fluid. Fig. 1 Fig. 2 CT-scan showing the thickened appendix (white arrow). A & B: Axial views. C: Coronal view. D: Sagittal view. Fig. 2 Abdominal ultrasound showing the thickened appendix of 7,5 mm of diameter in the right lower quadrant (white arrow), associated to fat stranding and free fluid. CT-scan showing the thickened appendix (white arrow). A & B: Axial views. C: Coronal view. D: Sagittal view. Subsequently, an exploratory laparoscopy was performed. Intraoperative findings were multiple peritoneal implants of endometriosis in the rectum, sigmoid colon, ovaries and fallopian tubes, and a thickened appendix, particularly its tip. There was scarce hematic free fluid and no other findings. We proceeded with a laparoscopic appendectomy and the biopsy of one of the peritoneal implants ( Fig. 3 ). Fig. 3 Exploratory laparoscopy. A & B: Intraoperative view of the appendix. White arrow showing the thickened tip of the appendix. C: Peritoneal implants at the sigmoid (white arrow). D: Peritoneal implants (white arrow) and hematic free fluid at the pelvis. Fig. 3 Exploratory laparoscopy. A & B: Intraoperative view of the appendix. White arrow showing the thickened tip of the appendix. C: Peritoneal implants at the sigmoid (white arrow). D: Peritoneal implants (white arrow) and hematic free fluid at the pelvis. On histopathological examination, the tip of the appendix was noted to be replaced by an endometrioma ( Fig. 4 ). The peritoneal implant biopsied was of endometrial tissue as well. Fig. 4 A: Photomicrograph shows normal appendiceal mucosa with simple cylindric epithelium and lymphoid elements (white arrow), with dilated endometrial glands and cytogenic stroma (black arrow) infiltrating smooth muscle tissue. Hematoxylin and eosin 40×. B y C: Endometrial glands surrounded by cytogenic stroma within the wall of the cecal appendix. Hematoxylin and eosin 100× (B) and 40× (C). D: Endometrial stroma surrounding the cystically dilated glands positive for CD10 (black arrow). Immunohistochemical technique 40×. Fig. 4 A: Photomicrograph shows normal appendiceal mucosa with simple cylindric epithelium and lymphoid elements (white arrow), with dilated endometrial glands and cytogenic stroma (black arrow) infiltrating smooth muscle tissue. Hematoxylin and eosin 40×. B y C: Endometrial glands surrounded by cytogenic stroma within the wall of the cecal appendix. Hematoxylin and eosin 100× (B) and 40× (C). D: Endometrial stroma surrounding the cystically dilated glands positive for CD10 (black arrow). Immunohistochemical technique 40×. The patient had an uneventful recovery and was discharged on postoperative day one. Outpatient controls at first and fourth postoperative week were unremarkable. The pain did not recur and no other symptoms were presented. She continued with gynecology follow-ups but did not require any long-term treatments.

There are no conflicts of interest to disclose.