Eight-Kilogramme Giant Mesenteric Cyst of Mullerian Origin: Case Report and Review of Literature

Mesenteric cysts are a rare occurrence in clinical practice, and even fewer are found to be of Mullerian origin. Diagnosis of mesenteric cysts is typically based on clinical assessment and radiological imaging. Surgical excision remains the primary treatment option. We report a case of a middle-aged lady presenting with a giant mesenteric cyst weighing 8-kilogrammes that was managed with laparotomy. Current literature of this rare clinical entity was also reviewed, including differential diagnoses of cystic lesions within the abdomen and role of imaging in guiding pre-operative diagnosis and management strategies. The giant mesenteric cyst was successfully excised en bloc without spillage via a laparotomy. Analgesia optimisation was achieved with a continuous local anaesthetic infusion. Pre-operative radiology can assist in diagnosis of the mesenteric cyst and guide management. Should an open surgical approach be selected, analgesia can be optimised with a continuous local anaesthetic infusion which decreases need for opioid medications.


Introduction
Mesenteric cysts are a rare occurrence in daily clinical practice, with an estimated incidence in the general adult population ranging from 1 in 27,000 to 250,000 [1,2].
The diagnosis of mesenteric cysts was traditionally difficult due to an absence of pathognomic clinical features and non-revealing serum biochemistry-consequently, many if not most mesenteric cysts were diagnosed at laparotomy [3], and anecdotally, large mesenteric cysts have been misdiagnosed as ascites and treated with repeated aspirations with limited success [4]. The advent of affordable, readily available and high-quality imaging modalities such as ultrasonography, computed tomography (CT) and magnetic resonance imaging (MRI) has allowed for an accurate means of pre-operative diagnosis and consequently allows planning of further management including laparoscopic or open approach to surgery. Once diagnosed, surgical excision via enucleation without spillage of cystic contents remains the mainstay of treatment.

Case Report
Our patient was a Chinese woman in her fifth decade with no significant past medical history aside from two previous normal vaginal deliveries. She was initially referred from her family physician for gynaecological evaluation of a possible giant ovarian cyst, prior to attending our clinic for a general surgical consultation. She complained of worsening abdominal distension over 1 year, associated with occasional dull, aching discomfort. She works as a physiotherapist and had intentional weight loss of 3-kilogrammes (kg) over 1 year from increased physical activity. She did not report any personal or familial history of malignancy. She did not have anorexia, early satiety or apparent changes in bowel habit. Her menstrual cycles were regular, and she did not have dysmenorrhoea. There was no significant history of genetic This article is part of the Topical Collection on Surgery. disorders and personal or family history of cancer. Physical examination revealed a grossly distended abdomen with positive fluid thrill, but no discretely palpable mass. Serum biochemistry were within normal range. Tumour markers including alpha fetoprotein (AFP), carcinoembryonic antigen (CEA), carbohydrate antigen 19-9 (CA 19-9) and cancer antigen 125 (CA 125) were not elevated.
Ultrasonography was pertinent for an anechoic uniloculated cystic mass occupying the entire abdomen and pelvis, with no sonographic features suggestive of a solid component, fat density, internal septations or mural nodules. CT scan of the abdomen and pelvis demonstrated a large unilocular cystic mass measuring 27.2 centimetres (cm) by 24.1 cm by 15.3 cm, extending from the epigastrium into the pelvis (Fig. 1). There were no septations, calcifications or soft tissue density within. Due to the massive size of the cyst, bowel loops and other abdominal viscera were displaced laterally into the right side of the abdomen, and there was also mild dilatation of both pelvicalyceal systems due to extrinsic compression by the mass. The urinary bladder, uterus and bilateral ovaries appeared normal and separate from the cystic mass.
In view of the immense size of the mass and the fact that it took up majority of the abdominal cavity, the laparoscopic approach was not feasible for en bloc enucleation without prior decompression of the cystic contents. The patient was counselled and agreeable for a laparotomy and excision of the cystic lesion. At laparotomy, the patient was found to have a large and tense cystic lesion arising from the descending colon mesentery, which displaced the collapsed sigmoid colon and small bowel loops into the right abdomen, corresponding to the appearance on preoperative CT scan (Fig. 2, image A). The huge mesenteric cyst was carefully dissected and successfully enucleated without spillage of cystic contents, need for intestinal resection or damage to adjacent viscera and mesentery.
On macroscopic examination, the excised cyst measured 39 cm in maximal dimension and weighed 8 kg. It had a thin, translucent wall, was uni-locular and contained clear serous fluid (Fig. 2, image D). Microscopic examination showed that the cyst was lined by tubal-type cuboidal epithelium and there was underlying loose spindle-cell stroma -features in keeping with those of a benign Mullerian cyst (Fig. 3).
The patient was placed on our institution's Enhanced Recovery After Surgery (ERAS) care bundle. Post-operative pain was managed by simple oral analgesia and continuous pre-peritoneal infusion of 2% ropivacaine local anaesthetic via an ON-Q PainBuster® elastometric pump (Avanos Medical Inc, USA), inserted at the conclusion of surgery (Fig. 2, image C). The patient was discharged on post-operative day 3. The patient remained clinically well and without recurrence at follow-up 3, 6 and 12 months post-surgery. No interval radiological imaging was performed as final histology was benign. Informed consent was obtained from the patient for publication of her case and relevant clinical, radiological and histopathological images for the purposes of research and medical education.

Discussion
Mesenteric cysts are rare entities with varied presentations. Their estimated incidence in the general adult population ranges from 1 in 27,000 to 250,000-consequently, most published studies consist of only a handful of cases [1,2].
The earliest report of a mesenteric cyst was by the Florentine anatomist Benevieni in 1507, who described a "callus of messaric veins" during the post-mortem examination of an 8-year-old boy. Von Rokitansky described the first chylous cyst in 1842, and Gairdner in 1852 reported the first omental cyst. The earliest successful resection of a mesenteric cyst was described by Tillaux in 1880, and in 1883, Pean detailed a technique of marsupialising mesenteric cysts. Only 600 cases had been reported in literature by 1954 [1][2][3].
Mesenteric cysts can arise within the mesentery of any part of the gastrointestinal tract, from duodenum to rectum. In a review series of 162 patients, 60% occurred in mesentery of small bowel, 24% in colonic mesentery, 14.5% arose in the retroperitoneum and the remaining 1.5% had uncertain origin [1]. These cysts are fluid-filled sacs lined with endothelium or mesothelium, and cysts ranging from 2 to 36 cm in diameter have been described in literature. These cysts may be uni-loculated, multi-loculated or septated and can contain serous, chylous, sanguinous or chylolymphatic fluid. Other cysts may arise in the retroperitoneum but are considerably more difficult to manage although they can present in a similar manner [1,5,6].
The differential diagnosis of cystic lesions within the abdomen and pelvis can be broadly divided into true cysts, cystic neoplasms and cystic-appearing lesions. Clinical and radiological differentiation can be difficult due to significant overlap in their presentation and appearance on imaging. The organ of origin can be obvious for small cystic lesions, which facilitates organ-based differential diagnosis. Larger cystic lesions tend to occupy a significant proportion of the abdominopelvic cavity and as such their anatomical origin may be unclear. The presence of solid nodules within a multilocular cyst is worrisome for possible malignancy or malignant potential, and thick-walled cystic lesions with solid components typically raise concern for mucinous cystic neoplasms or ovarian cystic neoplasms. True cysts such as mesenteric cysts are typically characterised by thin walls, absence of solid component and presence of only rare calcifications. Cystic neoplasms have a more complex appearance with presence of multiple locules, septa and calcifications. Examples include mucinous cystic neoplasms, peritoneal inclusion cysts (also known as multi-cystic peritoneal mesotheliomas) and pseudomyxoma peritonei. Cystic-appearing lesions are an entity encompassing pseudocysts, peritoneal hydatid cysts and appendiceal mucinous neoplasms [7].
Mesenteric cysts are most common in the fourth decade of life, and patients can present asymptomatically or with non-specific abdominal pain, abdominal distension, nausea and vomiting, constipation or diarrhoea [8]. Symptoms are usually present for a period prior to clinical presentation,  with a mean symptom duration of 2 to 6 months [1,9]. Ultrasonography and CT scans of the abdomen are favoured diagnostic modalities. The typical finding on ultrasonography is a hypoechoic cystic mass, whereas CT is usually pertinent for a fluid-filled cyst with thin walls. Both imaging modalities can also demonstrate size, septa, debris and abdominal fluid levels. CT scans occasionally identify the origin of the mass and its relation to neighbouring organs [7,9].
The mesenteric cyst in our case report was a benign Mullerian cyst, which falls under the category of urogenital origin. Mullerian cysts are most commonly found in the vagina, uterus and ovaries in females, in the prostate and seminal vesicles in males, in the lumbosacral paravertebral region and rarely in the mediastinum [11][12][13]. Mullerian cysts arising in the mesentery are hence exceedingly uncommon, with only a few case reports published in literature [11,[14][15][16][17][18]. Urogenital cysts are thought to be derived from vestiges of embryonic urogenital apparatus and can be subclassified into: pronephric, mesonephric, metanephric and Mullerian [14]. Alternative mechanisms proposed include differentiation of coelomic epithelium or peritoneum into tubal type epithelium [18]. Mullerian cysts (also known as paramesonephric cysts) are embryological remnants of the caudal ends of fused Mullerian ducts and are typically present if the Mullerian ducts fail to undergo complete agenesis in utero. In males, these ducts undergo full degeneration, while in females, the cephalad segments develop into the oviduct and the caudal segments fuse to form the uterus and upper vagina [11].
Nevertheless, surgical resection remains the mainstay of treatment for most cystic lesions within the abdomen [7]. The treatment of choice for mesenteric cysts is complete surgical excision -conventionally enucleation via an open approach, which also allows for simultaneous evaluation for other pathologies. More recently, successful resection by minimally invasive techniques has been described-the first report of laparoscopic enucleation was authored by Mackenzie in 1993. Laparoscopic resection of mesenteric cysts is increasingly gaining traction as an alternative approach to laparotomy, with cited benefits of reduced post-operative pain and analgesic requirement, shorter hospital stay, earlier return to daily activities and better cosmesis [19]. Aspiration or unroofing and marsupialisation of mesenteric cysts have been described in literature, but are generally not recommended if surgical excision is feasible because both of these options are associated with high risks of infection or recurrence [3,5,[20][21][22]. For abdominal cystic lesions suspected of malignancy or malignant potential, complete surgical excision without spillage or involved margins should be performed [2,7]. Conversely, pseudocysts can be managed with drainage and marsupialization -they often appear as a thick-walled cystic lesion with progressive mural enhancement and frequently contain septa or have surrounding inflammatory changes on CT imaging. Peritoneal hydatidosis can be managed with medication or complete surgical excision without spillage -ultrasonographic features include presence of daughter cysts, floating membranes, internal debris or calcification [7].
The risks of malignancy in mesenteric cysts reported in literature range from 3 to 22% [1,2,5]. Laparoscopic resection for larger mesenteric cysts invariably requires aspiration for dissection from surrounding structures or extraction from the abdomen, with attendant risks of spillage of cystic contents into the peritoneal cavity [19,23,24]. An open procedure was chosen for the patient in our case report due to the size of the cyst-the main concerns were that of inadvertent spillage of cystic contents during aspiration and insufficient working space in the peritoneal cavity for laparoscopy. While open surgery is associated with disadvantages including increased pain when compared to a laparoscopic approach, this was managed with the use of simple oral analgesia and continuous infusion of 2% ropivacaine local anaesthetic delivered at a rate of 7 millilitres (ml) per hour into the pre-peritoneal plane via an ON-Q PainBuster® elastometric pump, inserted during wound closure at the end of the patient's surgery. The usage of this device allows for effective analgesia without the requirement of strong opioids [25] and is a feasible strategy for balancing pain optimisation of open surgery and minimising intra-operative spillage of the excised cyst for larger lesions or those concerning for malignancy [7].