Appendiceal endometriosis mimicking acute appendicitis in a young woman: A case report

A 19-year-old woman with no significant past medical, gynecological, or obstetric history presented to the emergency department with acute right-sided abdominal pain associated with nausea and lightheadedness. She said that the pain had started suddenly while she was lying in bed. Her last menstrual period had occurred 20 days before presentation, and she was not on any contraceptive medication. On admission, her vital signs were stable with a blood pressure of 107/74 mmHg, heart rate of 85 beats/min, respiratory rate of 18 breaths/min, temperature of 98.6 °F (37 °C), and oxygen saturation of 99% on room air. Physical examination revealed tenderness in the right lower quadrant of the abdomen without rigidity or rebound tenderness. Murphy sign was negative, whereas Rovsing sign was positive. Digital rectal examination was unremarkable. Laboratory investigations showed a white blood cell count of 7000/μL with 63.7% neutrophils and 29.4% lymphocytes, hemoglobin of 12.9 g/dL, hematocrit of 39.4%, and platelet count of 299,000/μL. Serum electrolytes were within normal limits except for chloride of 109 mmol/L and bicarbonate of 21 mmol/L. Liver function tests were normal except for a mildly elevated aspartate aminotransferase level of 37 U/L. Serum lipase, creatine kinase, and thyroid function tests were within normal range. Urine pregnancy test was negative. The modified Alvarado score was calculated to be 4. A right upper quadrant ultrasound demonstrated a small hypoechoic area measuring approximately 1 cm in the pancreatic tail that was not well visualized; the remainder of the examination was unremarkable. The appendix was not clearly visualized in contrast-enhanced computed tomography (CT) of the abdomen and pelvis. Mild fluid and inflammatory changes were noted inferior to the base of the cecum extending toward the right adnexa, raising concern for acute appendicitis versus physiologic fluid or a ruptured ovarian cyst ( Fig. 1 ). The pancreas appeared normal on CT imaging. Fig. 1 CT scan of abdomen and pelvis in which the appendix was not clearly visualized (arrow). Mild fluid and inflammatory changes were noted inferior to the base of the cecum extending toward the right adnexa, raising concern for acute appendicitis versus physiologic fluid or a ruptured ovarian cyst. Fig. 1 CT scan of abdomen and pelvis in which the appendix was not clearly visualized (arrow). Mild fluid and inflammatory changes were noted inferior to the base of the cecum extending toward the right adnexa, raising concern for acute appendicitis versus physiologic fluid or a ruptured ovarian cyst. Subsequent pelvic ultrasound revealed a grossly normal uterus and left ovary. A complex cystic structure was identified within the right ovary, consistent with a possible corpus luteum cyst. Bilateral adnexal free fluid was present. In addition, right lower quadrant fluid and stranding with a lobular hypoechoic structure adjacent to the right ovary were noted, and appendicitis could not be ruled out as a differential diagnosis. Because of continued right lower quadrant pain and equivocal imaging findings, the general surgery department was consulted. Although the patient remained hemodynamically stable and did not exhibit leukocytosis, physical examination continued to demonstrate right lower quadrant tenderness with guarding. Because of the ongoing diagnostic uncertainty between acute appendicitis and a gynecologic etiology, antibiotics were deferred, the patient was kept nil per os overnight, and diagnostic laparoscopy with appendectomy was performed the following day. Intraoperatively, findings included acute appendicitis, hemoperitoneum, pelvic endometriotic implants, and a possible ruptured right ovarian follicle. Histopathological examination of the resected appendix revealed serosal endometriosis without evidence of transmural appendiceal involvement. Based on the intraoperative findings and pathology results, the patient's symptoms were attributed primarily to endometriosis involving the appendix. Postoperatively, pain was controlled with acetaminophen and oxycodone as needed, with stool softeners administered. She improved clinically with return of bowel function and was discharged in stable condition with surgical and gynecologic follow-up, including referral to an endometriosis center. She was counseled regarding endometriosis and advised that first-line hormonal therapy with combined oral contraceptives would be initiated in the outpatient setting after recovery.

No funding from an external source supported the publication of this case report.

Written informed consent was obtained from the patient for publication of this case report and accompanying image.

Appendiceal endometriosis is a rare manifestation of extragenital endometriosis that can closely mimic acute appendicitis, making preoperative diagnosis challenging. In reproductive-age women presenting with right lower quadrant abdominal pain and equivocal laboratory or imaging findings, endometriosis should be considered in the differential diagnosis. This case highlights the value of diagnostic laparoscopy and histopathological examination in establishing the diagnosis and identifying concomitant pelvic disease. Early recognition of appendiceal endometriosis may facilitate appropriate gynecologic follow-up and long-term management of endometriosis.

Endometriosis is a common gynecologic disorder affecting approximately 6–10% of women of reproductive age; however, appendiceal involvement is rare. Gastrointestinal endometriosis occurs in approximately 3–37% of women with endometriosis, with the rectosigmoid colon representing the most frequently affected site. Appendiceal endometriosis accounts for only a small proportion of gastrointestinal endometriosis cases and has been reported in less than 1% of women with endometriosis. [1] , [2] The clinical manifestations of appendiceal endometriosis are highly variable. Patients may be asymptomatic or present with chronic pelvic pain, dysmenorrhea, gastrointestinal symptoms, intestinal obstruction, intussusception, lower gastrointestinal bleeding, or acute right lower quadrant pain mimicking appendicitis. [1] , [2] , [3] Because symptoms are often nonspecific, preoperative diagnosis is challenging and is rarely established before surgical intervention. In most reported cases, the diagnosis is made incidentally following appendectomy and subsequent histopathological examination. [1] , [2] , [4] In this case, the patient presented with acute right-sided abdominal pain, nausea, right lower quadrant tenderness, and a positive Rovsing sign, findings that raised concern for acute appendicitis. However, the absence of leukocytosis, a modified Alvarado score of 4, and equivocal imaging findings created diagnostic uncertainty. Computed tomography demonstrated inflammatory changes near the cecal base extending toward the right adnexa, while pelvic ultrasonography revealed a possible corpus luteum cyst with adjacent free fluid. These findings broadened the differential diagnosis to include gynecologic etiologies such as ruptured ovarian cyst, ovarian endometriosis, or other causes of hemoperitoneum. Similar diagnostic dilemmas have been described in previous reports, highlighting the overlap between appendiceal endometriosis and acute appendicitis. [2] , [5] The pathogenesis of appendiceal endometriosis remains incompletely understood. Several theories have been proposed, including retrograde menstruation, coelomic metaplasia, and lymphatic or hematogenous dissemination of endometrial tissue. [1] , [4] Histologically, endometriotic implants may involve the serosa, muscularis propria, or submucosa of the appendix, with serosal involvement being among the more common patterns. Cyclic bleeding and inflammation within these ectopic implants may produce localized irritation, fibrosis, and symptoms resembling acute appendicitis. [1] , [2] , [4] An important feature of the present case is the coexistence of pelvic endometriosis, hemoperitoneum, and appendiceal serosal endometriosis identified during laparoscopy. Although intraoperative findings initially suggested acute appendicitis, histopathological examination demonstrated serosal endometriosis of the appendix. This finding supports the possibility that the patient's symptoms were primarily related to endometriosis involving the appendix and adjacent pelvic structures. The presence of a possible ruptured ovarian follicle may also have contributed to the clinical presentation, further complicating the diagnostic evaluation. Surgical management remains both diagnostic and therapeutic in patients with suspected appendiceal pathology. Laparoscopy allows direct visualization of the appendix and pelvic organs, facilitates appendectomy when indicated, and may identify concomitant gynecologic disease. In reproductive-age women presenting with right lower quadrant pain, careful intraoperative assessment of the pelvis is important because identification of endometriosis has implications for long-term gynecologic management and symptom control. [1] , [4] Appendiceal endometriosis, although rare, should be considered in reproductive-age women with right lower quadrant pain and inconclusive findings. Histopathological examination remains essential for definitive diagnosis and appropriate gynecologic follow-up.

This article was not commissioned and was peer reviewed.

During the preparation of this work the authors used ChatGPT (OpenAI) solely for language editing and grammar improvement. After using ChatGPT, the authors reviewed and edited the content output as needed and take full responsibility for the content of the publication.

Ruchik Kevadiya contributed to patient care, conception of the case report, acquiring and interpreting the data, drafting the manuscript, undertaking the literature review and revising the article critically for important intellectual content. Proma Dey contributed to patient care, acquiring and interpreting the data, drafting the manuscript, undertaking the literature review and revising the article critically for important intellectual content. Kunj Rajeshbhai Ghantiwala contributed to conception of the case report, interpreting the data, drafting the manuscript, undertaking the literature review and revising the article critically for important intellectual content. Priya Mishra contributed to interpreting the data, undertaking the literature review, drafting the manuscript and revising the article critically for important intellectual content. Pakhal Saketha contributed to interpreting the data, undertaking the literature review, drafting the manuscript and revising the article critically for important intellectual content. Ahmed Saleh contributed to patient care, conception of the case report and critical revising the manuscript for important intellectual content. All authors approved the final submitted manuscript.

Endometriosis is a chronic estrogen-dependent disorder which is characterized by the presence of endometrial glands and stroma outside of the uterine cavity. It affects approximately 8–10% of women of reproductive age and most commonly involves the ovaries, pelvic peritoneum, and uterosacral ligaments. Extragenital manifestation may occur in different locations, including the gastrointestinal tract, urinary tract, thorax, and abdominal wall. [1] Appendiceal endometriosis is an uncommon manifestation of gastrointestinal endometriosis. Gastrointestinal involvement has been reported in 3–37% of patients with endometriosis, while appendiceal involvement accounts for approximately 3% of gastrointestinal cases and less than 1% of all endometriosis cases. [1] , [2] Clinical presentation of this ranges from asymptomatic disease to chronic pelvic pain, cyclic right lower quadrant pain, gastrointestinal bleeding, intestinal obstruction, and symptoms that can mimick acute appendicitis. [1] , [2] Preoperative diagnosis of appendiceal endometriosis is difficult because its clinical manifestations and imaging findings are often nonspecific. Consequently, many patients undergo appendectomy for presumed acute appendicitis, with the diagnosis ultimately established by histopathological examination of the surgical specimen. [1] , [2] This case highlights the diagnostic challenge of appendiceal endometriosis in women of reproductive age presenting with right lower quadrant pain.

The authors declare that they have no competing interest regarding the publication of this case report.