Large intra-abdominal mucinous cystic adenoma: is it of ovarian or mesenteric origin

A 54-year-old female presented with a six year history of increasing abdominal swelling and discomfort and two months of intermittent constipation and difficulty with micturition. She was referred from the gynecological service having been investigated for a pelvic pathology without any positive findings. Her medical history was otherwise unremarkable. Physical examination revealed a non-tender intra-abdominal mass extending from epigastrium to the pelvis with a smooth surface. A large intra-abdominal multi-loculated cyst, separate from the ovaries, was seen on imaging. At laparotomy, the cystic tumour was discovered to arise from the mesentery of the terminal ileum and was resected en bloc. Histopathology revealed the tumour to be a benign mucinous cystadenoma, possibly of ovarian origin. This report aims to raise awareness of the difficulty of distinguishing ovarian from extra-ovarian mucinous cystadenomas on histopathological examination alone.


Introduction
Intra-abdominal mucinous cystic neoplasms commonly arise from the ovaries. When they are large and seemingly involve both the mesentery and adnexa, determination of their tissue of origin becomes problematic. Mucinous cystadenomas arising from extraovarian sites are very rare. They are mucin-producing cystic tumors with an ovarian-like stroma that may arise from the pancreas, liver, mesentery and spleen. Mesenteric cysts are so rare they are not usually considered in the differential diagnosis of intra-abdominal masses. Prior to 2009, there were only thirteen reported cases of mucinous cystadenoma (MCA) involving the mesentery [1]. We report a patient who presented with a large intra-abdominal cystic mass of debatable origin: the surgical findings supported a mesenteric origin but the histopathology report suggested an ovarian mucinous cystadenoma.

Patient and observation
The patient is a 54 year-old lady who presented with a six year history of increasing abdominal swelling and discomfort and two months of intermittent constipation and difficulty with micturition. The swelling and discomfort began in the lower abdomen. She was referred from the gynecological service having been investigated for a pelvic pathology without any positive findings. Her medical history was otherwise unremarkable. Physical examination revealed a non-tender intra-abdominal mass extending from epigastrium to the pelvis with a smooth surface ( Figure 1). The mass was mobile and dull to percussion. Rectal examination was normal. Her hemoglobin was 12.7g/dl, white cell count 3.9 x 10 9 /l, and ESR of 52mm fall/hour. Preoperative imaging usually involves ultrasonography and computed tomographic studies of the abdomen. Ultrasonography is the preferred diagnostic method [5] Other imaging modalities such as plain abdominal radiographs, computed tomography (CT) studies and magnetic resonance imaging (MRI) may be useful in selected cases.
When bowel involvement is uncertain, more advanced imaging techniques involving barium enema, CT and MRI could be more informative [6].
Of the thirteen cases of MCA of the mesentery reported prior to 2009, preoperative imaging was inconclusive in nine cases, suggested ovarian origin in four cases and mesenteric origin in only one case [1].
Because ovarian MCAs are relatively more common, extra-ovarian MCAs are commonly mistaken for the ovarian variety. Even more interesting is the fact that ovarian and extra-ovarian MCAs are essentially identical in histological features [7]. Histological examination alone is thus unsatisfactory in determining the origin of the tumor. The similarities between ovarian and extra-ovarian MCAs suggest a common pathway of development [8]. The cyst wall of extra-ovarian MCAs is lined by mucin-secreting flat, cuboidal or columnar epithelium associated with an underlying sub-epithelial ovarian like stroma. This is the same as may be found in ovarian MCA with the important distinction that when normal ovarian tissue is present, its stroma is distinctly different from the stroma of the septa found within the cyst [7]. The origin of extra-ovarian MCAs has been attributed to implanted or ectopic ovarian tissue, supernumerary ovaries, or mono-phyletic development of a teratoma component [1].
These tumors may become malignant [9] as well as have a propensity for distant metastasis of borderline-appearing lesions [10].

Conclusion
Large intra-abdominal mucinous cystadenomas may pose a diagnostic conundrum regarding their origin. Histopathological examination is inadequate in terms of differentiation between ovarian and extraovarian mucinous cystadenomas.

Competing interests
The authors declare no competing interests.