Mesenteric cysts are rare intraabdominal masses, with their incidence varying from 1 of every 100000 to 250000 admissions (1) and may occur in patients of any age with a male to female ratio 1:1 (2, 3). They are defined as cystic malformations of the mesentery and can be located anywhere at the mesentery from the duodenum to the rectum, but are found more frequently at the iliac mesentery (1,2). Mesenteric cysts usually remain asymptomatic with 40% of the cases being incidental findings, but they may also present with non-specific abdominal symptoms, such as pain, nausea and vomiting and even rarely they may be the cause of acute abdomen (1,2,3). We present a case of a mesenteric cyst in patient with colon cancer, which was considered to be a urinary bladder diverticulum in the CT scan.
A 83 years old woman referred to our department for surgical management of an adenocarcinoma of the right colon flexure. The patient's medical history included Parkinson disease, osteoporosis, hypertension and had undergone right modified radical mastectomy for breast cancer 6 years ago. One month earlier the patient had first presented with a mild abdominal pain, constipation and melena for about 10 days. Laboratory examination revealed hypochromic parvicellular anemia with a 24.9 % Ht and 7.9 g/dl hemoglobin. The colonoscopy showed a ulcerated-necrotizing invasive mass of the hepatic flexure that occupied the of the lumen and the biopsy revealed a poorly differentiated adenocarcinoma of the colon. The preoperative abdominal CT scan didn't reveal any metastases or lymphadenopathy, but revealed a 9x8 cm cystic mass of the right pelvic region that was considered to be a urinary bladder diverticulum as it seemed to have continuity with the wall of the urinrary bladder (figure 1).
During laparotomy a mesenteric cyst of the terminal ileum was found at about 30 cm from the ileocecal valve (figure 2). The cyst was closely associated to the bowel and involved the vessels of this part of the ileum. A right hemicolectomy was performed for the colon cancer which included the part of the ileum where the cyst was attached.
Histopathological examination of the cyst revealed a simple benign mesothelial cyst of the mesenterium. The cystic wall was consisted by loose fibrous tissue, oedematous same times, with many small vessels and focally lymphocytes' inflitration. The inner surface of the cystic wall was lined by a single layer of flattened or cuboid mesothelial cells that occasionally had a hobnail shape (figure 3).
The patient's postoperative course was uneventful and she was discharged after 12 days.
Mesenteric cyst is an uncommon clinical entity that was first described in 1507 by the Italian anatomist Benevenni during autopsy (4). They are classified based on histopathological features as following: 1) cysts of lymphatic origin (simple lymphatic cyst and lymphangioma); 2) cysts of mesothelial origin (simple mesothelial cyst, benign cystic mesothelioma, and malignant cystic mesothelioma); 3) cysts of enteric origin (enteric cyst and enteric duplication cyst); 4) cysts of urogenital origin; 5) mature cystic teratoma (dermoid cyst), and 6) pseudocysts (infectious and traumatic cysts) (5). In our case the cyst was considered a simple mesothelial cyst.
While the exact etiopathogenesis of mesenteric cysts is still unknown, they are considered to be the result of benign proliferations of ectopic lymphatic tissue that fail to communicate with the remaining lymphatic system, or of failure of the embryonic lymph channels to join to the venous system, obstruction or sequestration of the lymphatic vessels, abdominal trauma, neoplasia and local degeneration of lymph nodes (2, 3, 6). Mesothelial cysts are considered to be the result of mesothelial lined peritoneal surfaces that failed to coalesce (7).
Mesenteric cysts are usually located at the iliac mesentery but could be found anywhere at the mesentery from the duodenum to the rectum (1,2,3). They usually range in size from a few centimeters to over 10 cm and the symptoms are more likely to occur if the cyst's size is larger than 5 cm in diameter (2). Clinically, most mesenteric cysts are asymptomatic, but sometimes they present with non-specific abdominal symptoms such as abdominal distension, pain, nausea, vomiting, change in bowel habit, diffuse tenderness, and palpable mass (1, 2, 3, 4).
Preoperative diagnosis can be aided using US, CT and MRI but careful interpretation of the images and high index of suspicion of this rare condition is essential for the correct diagnosis, which cannot always be established. In our case the intrabdominal cyst was falsely considered to be a urinary bladder diverticulum and the correct diagnosis of mesenteric cyst was made intraoperatively. Imaging techniques are helpful in determining the point of origin, the anatomical relationships with the adjacent organs, the size of the cyst, the density of the cystic fluid and the length of the cystic wall (2,3 ,4.). Mesothelial cysts are usually unilocular, with no internal septation, and in the US appear like an anechoic mass with acoustic enhancement, while in the CT and MRI show a fluid-filled mass with no discernible wall (7).
The therapeutic method of choice is complete surgical excision of the cyst, which minimizes the possibility of recurrence and can be performed either with laparotomy or laparoscopy (1,2,3, 6). Partial resection, aspiration or marsupialization of the cyst result in high recurrence rate and are considered suboptimal treatment and should only be performed in large cysts involving vital structures (6, 8) In a few cases bowel resection is necessary for the complete removal of the cyst as it involves blood vessels that supply the bowel or is closely associated to the bowel (3). In our case the cyst was excised during laparotomy performed for the right colon cancer.
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