Primary retroperitoneal mucinous cystic tumors with borderline malignancy (PRMCs-BM) are rare.1 Although they resemble ovarian mucinous neoplasms, they have been reported in women with normal ovaries.2 There is no consensus regarding their genesis, and because of their extreme rarity, their histogenesis, biological behavior, and optimal management strategy remain speculative. We herein describe a case of a PRMC-BM and review the pertinent literature.
A 65-year-old nulliparous woman was referred to our department for abdominal distention. Her medical history included a hysterectomy for leiomyoma at 40 years of age. She also underwent a single salpingooophorectomy at the same time, although no further information about this operation was available. Pelvic examination revealed a soft tumor extending from the pelvis to the left abdominal cavity. Ultrasonography of the pelvis confirmed the presence of a large multilocular cystic mass measuring 20 cm in size (Figure 1A). Subsequent magnetic resonance imaging (MRI) revealed a rounded cystic lesion that filled almost the entire pelvis (Figure 1B). Her serum cancer antigen 125 level was within the normal range. Hormonal tests were not performed.
The preoperative diagnosis was a cyst of the left ovary. An exploratory laparotomy was performed to further evaluate the mass, which was located in the left retroperitoneal space with no connection to other intra- or extra-abdominal organs. It was then completely resected without any complication. The tumor did not spread into the abdominal cavity.
Gross pathological examination revealed a thinly capsulated, multilocular cystic mass containing mucoid material and measuring 21×14 cm in diameter (Figure 2A). Small papillary areas were noted inside the cyst wall. Histologically, a single layer of both endocervical-like and intestinal-type columnar cells without atypia lined the cyst wall (Figure 2B). In the papillary area of the tumor, the cells displayed mild to moderate nuclear atypia and stratification of two to three layers but no stromal invasion (Figure 2C). Ovarian tissue was not observed.
The final diagnosis was PRMC-BL. At her 1-year follow-up, the patient remained free of disease.
PRMCs are uncommon neoplasms that occur almost exclusively in women, with only three cases reported in men.2-4 There are three clinicopathologic types of PRMCs: mucinous cystadenoma, PRMC-BM, and mucinous cystadenocarcinoma. We performed a literature review of PRMC-BM using MEDLINE® and identified only 12 cases from 11 reports published since 1988 (Table 1).1,3,5-13 Therefore, the incidence of PRMC-BM is extremely rare.
In previous reports of PRMC-BM, most patients were asymptomatic or experienced mild symptoms of distention, and pain owing to the mass was rare. The tumors were relatively large, ranging from 10 cm to >20 cm in diameter, and they were large enough to cause symptoms such as abdominal fullness.10 Preoperative diagnosis of PRMC-BM is very difficult, because not only are the tumors often overlooked in differential diagnoses but also there are no available sensitive methods or reliable markers.8 As retroperitoneal mucinous tumors are histologically similar to ovarian mucinous cystadenomas, ultrasonography, computed tomography, and MRI are usually not useful for distinguishing between them.10 Although aspiration is a good method for delineating the nature of the cyst, cytologic analysis of the aspirated fluid frequently fails to reveal the type of epithelial cells lining the cyst. Therefore, exploratory laparotomy with complete excision of the cyst is usually indicated for both the diagnosis and treatment of PRMCBM.8 Retroperitoneal mucinous tumors of epithelial origin are rare because epithelial cells do not normally exist in the peritoneum; therefore, their origin has been debated. Several hypotheses have been proposed to explain their genesis. The majority of these hypotheses suggest that they arise either from ectopic ovarian tissue in teratomas in which the mucinous epithelium has overridden all other components to become the only identifiable component, or from intestinal duplication, also known as enterogenous genesis.10,14 PRMCs are histologically similar to mucinous cystadenomas found in the ovaries. However, ovarian tissue has been observed in only one reported case of PRMC,15 and it was not observed in the present case. Furthermore, PRMCs have been previously reported in men. These findings exclude heterotopic ovarian tissue as the origin of PRMCs. Enterogenous genesis from intestinal duplication can also be excluded owing to the lack of well-developed intestinal mucosa and smooth muscles in PRMCs. The possibility of a monodermal variant of teratoma is unlikely because of the lack of other tissue types or typical structures of teratomas in PRMCs.8,10
A PRMC tumor should be treated in the same manner as a primary ovarian tumor of similar grade and comparable stage. In previously described cases of PRMC-BM, only tumor resection was performed, and no recurrence or metastasis was reported.10 Therefore, the long-term prognosis of PRMC-BM seems to be quite good as no evidence of disease was observed even after a follow-up period of up to 148 months.13 In the present case, we followed the patient every 6 months with pelvic ultrasonography examination. Her post-operative pelvic imaging showed no abnormalities, and her serum cancer antigen 125 levels remained within the normal range. Because of the small number of PRMC-BM cases reported in the international literature, investigators cannot justify the use of any adjuvant chemotherapy protocols. Surgery seems to be sufficient for the treatment of PRMC, especially if there is no eruption of the capsule in the cystadenoma. Some authors recommend chemotherapy for the treatment of PRMC cystadenomas and cystadenocarcinomas because their mechanisms of histogenesis may be the same as those of mucinous tumors of the ovaries.16,17 The small number of globally registered cases, the insufficient amount of surveillance data, and mainly, the inability to identify patients at a high risk of recurrence support the need for effective registration and further study of these rare tumors.18
In our case, no recurrence was observed during a follow-up period of 12 months. As there are no clear recommendations for surveillance of patients with PRMC-BM, we propose clinical examinations and ultrasonography every 6 months, as well as imaging studies every year using either MRI or computed tomography.