INTRODUCTION
Clinicians encountering patients with pelvic masses should consider diseases originating from the urogenital or colorectal regions, including tumors originating from the appendix. Appendiceal mucocele is a rare mucin-producing neoplasm of appendiceal origin. Because no clinical symptoms distinguish it from other pelvic diseases, the diagnosis of appendiceal mucocele can be challenging for many clinicians. Due to its location and imaging findings, appendiceal mucocele is easily confused with tumors originating from the right adnexa, such as right ovarian benign masses or cysts, or even malignancy [1,2]. We report a case of a patient with an appendiceal mucocele initially misdiagnosed as an ovarian malignancy before surgery. This is a rare case of a mistaken ovarian tumor because all preoperative imaging tests, including magnetic resonance imaging (MRI), suggested a right borderline tumor of ovarian origin. Informed consent was obtained from patient involved in the study.
CASE REPORT
A 66-year-old postmenopausal woman was admitted to the gynecology department for an asymptomatic pelvic mass incidentally discovered during a medical check-up. She had a medical history of hypertension and asymptomatic carotid artery stenosis. Her personal surgical and familial histories were unremarkable. Physical examination revealed a non-tender, palpable mass in the right lower quadrant. The results of the other abdominal examinations were unremarkable. Gynecological examination showed a normal uterus and cervix.
In the initial laboratory tests, the complete blood and white blood cell differential counts were unremarkable. The chemistry, coagulation panels, and urine analysis were also unremarkable. The levels of tumor markers, including carcinoembryonic antigen (CEA; 3.95 ng/mL), carbohydrate antigen 19-9 (CA19-9; 9.41 U/mL), and cancer antigen 125 (CA125; 5.84 U/mL), were normal.
The transvaginal ultrasound showed a normal uterus, with a well-defined mass with heterogenous echogenicity on the right side, measuring 80×54 mm. The left adnexa was normal in ultrasound. Preoperative pelvic MRI showed an 8-cm cystic mass with high signal intensity in T2-weight imaging. The mass had internal septa with subtle enhancement. The formal reading by a radiologist was an epithelial borderline tumor from the right ovary. No enlarged lymph nodes or ascites were observed in the pelvic and abdominal areas. The left ovary and uterus were also unremarkable (Fig. 1).
Explorative laparoscopy was performed by the gynecologic department. The intraoperative findings included a huge cystic mass in the right pelvic area. The uterus and both fallopian tubes and ovaries were normal. The other specific findings were unremarkable. The general surgery department was called into the operating room to confirm that the mass originated from the appendix. Both the cystic portion and the base of the appendix were enlarged to similar diameters similar to that of the cecum. Serosal invasion, regional lymph node enlargement, and ascites were not observed. There were no suspicious findings of peritoneal seeding in peritoneum and liver. Based on these findings, laparoscopic appendectomy was performed using a linear stapler (Powered ECHELON FLEX stapler, Ethicon), without any damage to the adjacent organs, including the cecum and ovary.
Gross examination revealed an enlarged appendix measuring 9.5×5.0×5.0 cm. The distal portion was whitish in color had had a huge cystic feature, while the proximal portion had a serosal appearance and was enlarged. The lumen was filled with mucoid material and was not perforated (Fig. 2).
Histopathological examination confirmed a low-grade mucinous neoplasm (LAMN) originating from the appendix. The resection margin was clear. The patient was discharged on the fifth postoperative day without any complications. The outpatient follow-up performed approximately 1 month later showed no evidence of disease progression or any other symptoms. Colonoscopy was performed for postoperative follow-up 6 months later and there were no remarkable findings.
DISCUSSION
Appendiceal mucocele may result from the accumulation of mucin that causes obstruction and dilation of the appendix and cecum. This condition is observed in 0.2% to 0.7% of all appendix specimens. It can be asymptomatic or present a variety of symptoms. Appendiceal mucocele may be discovered incidentally in radiologic or endoscopic tests or during surgery for other reasons [3,4]. Appendiceal masses usually show similar symptoms to appendicitis or adnexal masses, including pain in the right lower quadrant or pelvic area and palpable masses or enlarged intra-abdominal structures in imaging studies such as computed tomography (CT) or ultrasound.
Previous reports have proposed ultrasound as a preliminary diagnostic tool. A threshold appendix diameter of ≥15 mm for the diagnosis of appendiceal mucocele has an 83% sensitivity and 92% specificity. CT is the method of choice for better characterization of appendiceal mucocele [5]. Other reports have suggested that if appendiceal mucocele is suspected, and there are no abnormalities in the right ovary in imaging studies, it may be helpful to identify the “layered structure (onion skin sign)” by transabdominal ultrasound. Previous studies reported mucinous tumors in the appendix and ovary of 16 of 89 female patients. Moreover, the onion skin sign was present in patients with appendiceal mucocele but not in those with ovarian mucinous tumors. Thus, even when normal ovaries are not detected, clinicians observing the onion skin sign in the lower abdominal area by ultrasound should strongly consider appendiceal mucocele [5,6]. Moreover, if appendicitis is suspected and the diameter of the appendix on the CT scan is ≥1.3 cm, appendiceal mucocele should also be considered [5].
A literature review of the PubMed/MEDLINE, Google Scholar, and Web of Science databases from 2000 to 2022 as searches of Science Citation Index (SCI) and Scopus journals revealed similar cases of appendiceal mucocele mimicking adnexal lesions, as summarized in Table 1 [2,4,7–14]. A total of 18 cases of tumors originating from the appendix were preoperatively diagnosed as tumors originating from the adnexa. Most patients showed abdominal pain or palpable masses; however, five cases were asymptomatic and incidentally diagnosed. For preoperative diagnosis, ultrasound was performed in 15 cases (11 cases by transvaginal, 4 cases by transabdominal), CT was performed in seven cases, and MRI was performed in six cases.
In the present case, imaging studies, including ultrasound and MRI, were performed. However, the results indicated a right ovarian borderline tumor and the appendix appeared unremarkable. In the operative findings, the appendix looked like a tubular structure owing to the enlarged appendiceal orifice. Therefore, the radiologic characteristics differentiating the appendix from the cecum by MRI might have disappeared. Laparoscopic appendectomy was performed in six cases, conventional open appendectomy was performed in nine cases, and right hemicolectomy was performed in three cases. The cases that underwent right hemicolectomy were diagnosed with LAMN based on the findings of the pathologic reports.
The surgical method was determined according to the lesion characteristics and size as identified in preoperative imaging. In operative findings, if a perforated appendix, positive pelvic fluid cytology, or enlarged periappendiceal lymph node are observed surgeons should perform a right hemicolectomy. Otherwise, patients require only appendectomy or cecectomy [3]. In three cases that underwent a right hemicolectomy and in which LAMN was diagnosed the patients were overtreated in emergency operations. However, in our case, the gynecology department quickly detected the normal findings of the female genital organs and called the general surgery department to the operating room to avoid inappropriate procedures. Thus, appropriate minimal invasive surgery was performed in this elderly patient. However, a multidisciplinary team approach may have preoperatively determined a proper management plan.
Measurement of tumor markers was selectively performed according to the nature and size of the preoperative lesion and patient history. In most cases, the tumor marker levels were in the normal range; however, two cases showed elevated levels. The patients in those cases were diagnosed with malignancy and had a history of surgery with malignant ovarian teratoma.
There remains controversy regarding the usefulness of tumor markers. Some studies have been reported the diagnostic and prognostic value of tumor markers such as CEA and CA19-9 in appendiceal mucocele. However, other studies reported that they did not significantly improve diagnosis and prognosis. In the present case, the CEA and CA19-9 and CA125 levels were unremarkable [10].
Appendiceal mucocele can cause terrible complications such as peritoneal seeding or pseudomyxoma peritonei if appendiceal mucocele ruptures in the intra-abdominal space during surgery, remains in the surgical margin, or mucinous adenocarcinoma is confirmed. Histologic type is an important factor for planning treatment options including the range of surgical resection. Unfortunately, there remains controversy regarding histological classifications and terminology, which are not yet established for appendiceal mucinous neoplasm in various academic societies.
The most recently announced classification was released in 2010 by the World Health Organization (WHO), which included three categories of appendiceal mucocele: mucinous adenoma, low-grade appendiceal mucinous neoplasm, and mucinous adenocarcinoma. In 2016, the Modified Delphi Consensus was released by the Peritoneal Surface Oncology Group International (PSOGI). In addition to the three categories included in the WHO classification, the histological characteristics were further subdivided for a total of eight categories [15].
The literature review revealed seven cases of appendiceal mucinous cystadenoma, nine cases of LAMN, one case of appendiceal mucinous adenocarcinoma, and one case of retention cyst. The diagnosis of LAMN in the present case was pathologically confirmed.
While there is no standard surgical treatment protocol and margin positivity, many surgeons have performed and recommended surgical treatment depending on the histological classification. Patients with LAMN usually require appendectomy alone, while patients with mucinous adenocarcinoma require right hemicolectomy. If peritoneal seeding or pseudomyxoma peritonei are suspected, surgeons should consider debulking surgery or hyperthermic intraperitoneal chemotherapy [5].
Appendiceal mucocele is a rare disease that is easily confused with other pelvic diseases. Therefore, physical examinations, proper imaging studies, and laboratory tests including tumor markers are helpful to determine the management plan.
However, in this case, even with sufficient imaging studies, examinations, and imaging readings by a well-trained radiologist, the preoperative diagnosis was not accurate. Surgeons encountering masses in the pelvic area should be aware of the various possibilities, including appendiceal mucocele.
Therefore, it is important to determine the origins of lesions in the pelvic cavity. A proper preoperative clinical work-up and management plan should be performed, and a multidisciplinary team approach involving gynecologists, surgeons, radiologists, and pathologists is needed to provide better detection and treatment for rare conditions such as our case. This manuscript introduces the interesting case and imply on the importance of caution for the possibility of unexpected pathology. Because of the risk of spillage of mucin from appendiceal mucocele during surgery, gentle touch and complete excision of appendix including tumor is needed.
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