World Journal of Surgical Oncology Open Access Mucinous Cystic Neoplasms of the Mesentery: a Case Report and Review of the Literature

Background: Mucinous cystic neoplasms arise in the ovary and various extra-ovarian sites. While their pathogenesis remains conjectural, their similarities suggest a common pathway of development. There have been rare reports involving the mesentery as a primary tumour site.


Case presentation
A 22 year old white-Caucasian female, with otherwise unremarkable history, presented with chronic, left sided, vague abdominal pain. There were no abnormal findings on clinical examination. Ultrasound (US), computerized tomography (CT) and magnetic resonance (MR) scans ( Fig. 1a, b) demonstrated a unilocular cystic mass measuring 8.5 × 6 × 3.5 cm and lying medially to the descending colon. No definite preoperative diagnosis could be established. At laparotomy the mass was fixed within the descending and sigmoid colonic mesentery (Fig. 2). As there were no firm adhesions or shared blood supply (Fig.  3), enucleation was easily performed. The cyst had a macroscopically thin and smooth wall and contained whiteyellowish fluid. The cyst wall was examined in its entirety. Histology demonstrated two distinct components: an outer ovarian-like stromal layer, composed of densely packed spindle-shaped cells (Fig. 4) and an inner epithelial layer, consisting of cuboidal and columnar mucinous cells (Fig. 5, 6). Immunohistochemical study of the stromal cells demonstrated positivity for vimentin, actin, and desmin. The epithelial cells showed positivity for cytokeratin-7 (Fig. 6), CA-125 (Fig. 7), CEA, and CA 19-9 and negative expression of cytokeratin-20. There was no cellular atypia. The overall features suggested a benign neoplasm of epithelial origin with the appearance of an ovarian mucinous cystadenoma. The patient recovered uneventfully and remained well on annual follow-up with abdominal US.

Discussion
There are thirteen documented cases of mesenteric MCNs in the literature prior to this report ( Table 1). Five of those originated from the mesentery of the small intestine [15,18,[51][52][53], one from the mesoappendix [54] and seven from the mesocolon [55][56][57][58][59][60]. The only male patient was a five year old child with an unresectable neoplasm [15]. Clinical presentation typically involved chronic abdominal pain (n = 8) and distention (n = 5). Three patients were asymptomatic and one presented with acute manifestation of symptoms. Interestingly, preoperative imaging was inconclusive in nine cases, suggested ovarian origin in four cases, and mesenteric origin in only one case. No pathognomonic malignant features were illustrated. Pathology reported nine benign mucinous cystadenomas (including the present case), three borderline MCNs, (based on the presence of atypical nuclei, pseudostratification, glandular arrangements and lack of invasion) and two carcinomas. The median age at diagnosis of benign mesenteric MCNs was 26.1 yrs, compared to 35.2 yrs for non-benign tumours. One of the carcinomas [51] was thought to be the result of malignant transformation following earlier incomplete excisions of a recurrent benign tumour. One of the patients with a borderline tumour, presented with metastatic disease in the mediastinal lymph nodes four years after removal, which may represent a missed invasive focus due to incomplete examination of the entire neoplasm wall. This patient had initially undergone a partial colectomy and salpingooophoretomy [55]. Another two patients underwent partial colectomies due to cyst wall adhesions, while enucleation of the tumor was performed in six. Partial cystectomy was performed in two unresectable tumors. Immunohistochemistry was reported in four cases. There was no report of ectopic ovarian tissue or evidence of teratomatous developement. There was no association between the age and tumor size.

Pathogenesis and biologic behavior of extra-ovarian MCNs
The origin of extra-ovarian MCNs has been sporadically attributed to implanted or ectopic ovarian tissue [61], supernumerary ovaries [62,63] or mono-phyletic developement of a teratoma component [64][65][66]. A recent concept linked the development of hepatic and pancreatic MCNs to the migration of epithelial cells from the embry-Intra-operative appearance, medial view of the mesentery, inferion mesenteric vessels lying on the cyst surface Figure 2 Intra-operative appearance, medial view of the mesentery, inferion mesenteric vessels lying on the cyst surface.
Lateral view of mesentery, cyst enucleation in an avascular plane Figure 3 Lateral view of mesentery, cyst enucleation in an avascular plane.
Microscopic appearance of the cyst wall, ovarian like stroma, epithelial lining Figure 4 Microscopic appearance of the cyst wall, ovarian like stroma, epithelial lining.
Benign columnar mucinous epithelium lining of the cyst wall According to the WHO classification (ICD 10), MCNs are divided into benign adenomas, borderline tumours, noninvasive (in situ) and invasive carcinomas. The malignant potential of all MCNs is supported by observations of malignant transformation of benign neoplasms during long term follow up [24,51]. Other authors noticed a frequent concurrence of benign and focally borderline or/ and malignant epithelium [21,72,73]. Also, as illustrated in the present study and previous pancreatic MCNs series [72,74], the median age at diagnosis is higher for malignant MCNs, which implies progression from adenoma to carcinoma. Consequently, failure to excise or study the entire cyst wall may result in the miscategorization of a neoplasm [75].

Classification of mesenteric cysts and cystic tumors
None of the recognized classifications of mesenteric cysts [81-85], has included MCNs up to date. Malignant mesothelioma is suggested as the only potential primary cystic malignancy in the mesentery. We found three more cases of primary mesenteric cystic neoplasms in the literature [86][87][88], as well as reports of mesenteric hydatid [8,[89][90][91][92]] and tuberculous cysts [93][94][95]. In view of the existing data, we propose an updated classification of mesenteric cysts and cystic tumors, as shown in the Appendix.

Diagnosis and treatment
There is no definitive diagnostic test. Radiological examinations may suggest the origin of a cyst, but cannot exclude the malignant potential of an MCN [35,82,84,[96][97][98][99]. Guided aspiration cytology and fluid analysis is rarely diagnostic, has a high false negative incidence [100] and may only be helpful in the complicated management of pancreatic cystic masses [101,102]. The definite diagnosis remains postoperative and therefore intra-operative frozen section does not have any use. Following exclusion of non-surgical conditions, complete excision is the only treatment option for all mesenteric neoplasms [103][104][105] because of their malignant potential as well as the high recurrence rate of benign tumors -such as lymphangiomas and mesotheliomas -after incomplete resection [106][107][108]. Open or laparoscopic approach depends on the surgeon's skills, as more complicated resections may be required [109][110][111]. Only one mesenteric MCN has been treated laparoscopically up to date, by a gynaecologist [54].

Conclusion
Mucinous cystic neoplasms of the mesentery present almost exclusively in women and must be considered in the differential diagnosis of mesenteric tumors. Whilst there are no pathognomonic diagnostic criteria, a mesenteric cyst should be approached as potentially malignant especially in adults. Only complete excision and full histological examination of a mucinous cystic neoplasm can exclude a borderline or malignant component. We propose an updated classification of mesenteric cysts.

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

Competing interests
The authors declare that they have no competing interests.