Primary Retroperitoneal Mucinous Cystadenoma

Twenty-nine-year-old woman presented with a 3-year history of left-sided abdominal discomfort. Her medical history includes hyperthyroidism. Physical examination revealed a large, fixed mass in her left abdomen. Routine blood tests were unremarkable. Ultrasound showed ovarian cysts and a 15-cm left adnexal cystic lesion. Magnetic Resonance Imaging (MRI) further delineated a 19 cm cystic lesion suggestive of a peritoneal mesothelial cyst (Figure 1). Following bilateral ovarian cystectomies, she underwent a secondary laparoscopy where a large 20 × 10 × 10 cm retroperitoneal mass was noted, adherent to the descending colon and displacing it to the right (Figure 2). The operation was converted to an open approach to allow complete excision of the cyst without content spillage. Histology showed mucinous epithelium positive for CK7 and PAX 8, negative for CK20, SATB2, calretinin, ER, and PR (Figure 3). No features of malignancy or ovarian stroma were identified. Findings were consistent with a primary retroperitoneal mucinous cystadenoma. Retroperitoneal mucinous neoplasms (RMN) are rare tumours. Formal diagnosis of RMN is based on their histological features and are classified into three categories: benign mucinous cystadenoma, mucinous borderline tumours, and mucinous carcinoma [1]. PRMCs mainly occur in women of childbearing age (median age = 36); only three male cases have been reported in the literature to date [2]. A few theories for the origin of RMNs have been proposed. One suggests ectopic ovarian tissue arising from the retroperitoneum, given its immunohistological similarity to ovarian mucinous tumours [3], though disputing this theory is the lack of ovarian stroma in many cases and the presence in males. A more popular theory currently is the invagination of peritoneal mesothelium, which then undergoes mucinous metaplasia; this is further supported by negative staining for oestrogen or progesterone receptors [1-7]. Due to its insidious onset and ambiguous presentation, preoperative diagnosis can be challenging yet important due to the possibility of malignant transformation [4, 5]. Clinically, patients usually present with chronic abdominal pain or a palpable mass. Ultrasound is a good initial investigative tool, especially in the young female population. However, further evaluation with computed tomography (CT) or MRI is necessary to characterise the lesion and aid in surgical planning. Our patient presented with vague non-specific symptoms, with multiple ovarian cysts resulting in an initial diagnostic conundrum requiring systemic workup and a secondary procedure for resection of the retroperitoneal cyst. All reported cases to date have been managed surgically with complete resection of the cyst. Surgical approach via laparoscopy or laparotomy is dependent on the surgeon's preference as there is currently not enough data to prove the superiority of one technique over the other. However, there has been a shift towards laparoscopic resection in recent years given the advances in minimally invasive surgery which has been shown to be safe and effective [5]. No PRMC recurrence has been reported in the literature, and its long-term survival rate is excellent at 100%, though it is much lower for mucinous carcinomas at 68% [8]. Primary retroperitoneal mucinous cystadenoma is a rare benign tumour with the potential for malignant transformation. CT and MRI can assist in the workup, though diagnosis is based on histology alone. Complete surgical resection without spillage of cyst content is the recommended management. Yusi Liu: investigation, validation, visualisation, writing – original draft, writing – reviewing and editing. Wei Ming Ong: conceptualization, project administration, resources, supervision, writing – reviewing and editing. Alex Wong: conceptualization, project administration, resources, supervision. Our gratitude goes to Dr. Ann Niap and Miss Xinyi Wei for their contribution to the content. Open access publishing facilitated by Monash University, as part of the Wiley - Monash University agreement via the Council of Australian University Librarians. Written consent from the patient was obtained for the presentation of her case for educational purposes. The authors declare no conflicts of interest.