Mesenteric and Omental Cysts 

In 1907, the Italian anatomist Benevieni first reported a mesenteric cyst following an autopsy on an 8-year-old girl.^[1] In 1842, von Rokitansky described a chylous mesenteric cyst.^[2] Gairdner published the first report of an omental cyst in 1852.^[3] Tillaux performed the first successful surgery for a cystic mass in the mesentery in 1880.^[4]

Frequency

Mesenteric and omental cysts are rare; the incidence is about 1 per 140,000 general hospital admissions and about 1 per 20,000 pediatric hospital admissions.^{[5, 6, 7]} In a study from Egleston Children's Hospital at Emory University from 1965-1994, 14 patients were treated for mesenteric or omental cysts, which represents a prevalence of about 1 case per 11,250 admissions.^[8] Approximately one third of cases occur in children younger than 15 years.^{[9, 10, 11]} The mean age of children affected is 4.9 years.^{[9, 11, 12, 13, 14, 15, 16]} Mesenteric cysts are 4.5 times more common than omental cysts.^[17]

As proposed by Gross, mesenteric and omental cysts are thought to represent benign proliferations of ectopic lymphatics that lack communication with the normal lymphatic system.^{[9, 18, 19]} Cysts are thought to arise from lymphatic spaces associated with the embryonic retroperitoneal lymph sac, making them analogous to cystic hygromas, which arise in the neck in association with the jugular lymph sac.^[20] Another proposed etiology is lymphatic obstruction;^[21] however, experimental occlusion of lymphatic channels in animals does not produce mesenteric or omental cysts because of the rich collaterals in the lymphatic system, which sheds doubt on this particular theory.^{[6, 18, 20]} Other etiologic theories include (1) failure of the embryonic lymph channels to join the venous system, (2) failure of the leaves of the mesentery to fuse, (3) trauma, (4) neoplasia, and (5) degeneration of lymph nodes.^[8]

Mesenteric cysts can occur anywhere in the mesentery of the gastrointestinal tract from the duodenum to the rectum, and they may extend from the base of the mesentery into the retroperitoneum.^{[8, 6]} In a series of 162 patients, 60% of mesenteric cysts occurred in the small-bowel mesentery, 24% in the large-bowel mesentery, and 14.5% in the retroperitoneum. They most commonly occur in the ileal mesentery of the small bowel or the sigmoid mesentery of the colon.^[5] Omental cysts are confined to the lesser or greater omentum.^[22]

Mesenteric and omental cysts can be simple or multiple, unilocular or multilocular, and they may contain hemorrhagic, serous, chylous, or infected fluid.^[8] The fluid is serous in ileal and colonic cysts and is chylous in jejunal cysts.^{[7, 11]} They can range in size from a few millimeters to 40 cm in diameter.

Mesenteric and omental cysts can be discovered as an incidental finding during laparotomy for another condition or they can manifest as an acute life-threatening intra-abdominal catastrophe.^[22] Children generally present with abdominal distention and few associated symptoms other than vague abdominal pain with or without a palpable mass.^{[21, 23]} The mass may be huge, simulating ascites.^[24] The most common mode of acute presentation in children is that of a small-bowel obstruction, which may be associated with intestinal volvulus or infarction.^{[11, 13, 15]}

Approximately 10% of patients with mesenteric and omental cysts present with an acute abdominal emergency.^[22] These masses can be detected using prenatal ultrasonography and appear as a sonolucent mass. The prenatal differential diagnosis includes dilated bowel (eg, intestinal atresia), dilated stomach (eg, pyloric atresia), gastrointestinal duplication, hydronephrosis, ovarian cyst, and cystic teratoma.

In a series of 82 children who underwent surgery for various causes of intestinal volvulus, mesenteric cysts were the underlying etiology in 3.65% of cases.^[25] A very unusual presentation of a mesenteric cyst is that of an irreducible inguinal hernia.^[1] The differential diagnosis includes intestinal duplication cyst; ovarian, choledochal, pancreatic, splenic, or renal cysts; hydronephrosis; cystic teratoma; hydatid cyst; and ascites.^[22]

In children, the most common indication for surgical intervention is the presence of an abdominal mass with or without signs of intestinal obstruction. Various complications have been associated with mesenteric and omental cysts, including intestinal obstruction (most common), volvulus, hemorrhage into the cyst, infection, rupture, cystic torsion, and obstruction of the urinary and biliary tract.^[22] Malignant transformation of mesenteric cysts has occurred in adults,^[5] but malignant mesenteric and omental cysts have not been reported in children.^[22]

Mesenteric cysts most commonly occur in the small-bowel mesentery on the mesenteric side of the bowel. Mesenteric cysts can often be shelled out from between the leaves of the mesentery while taking care to avoid damage to the mesenteric vessels,^[21] or they may require concomitant bowel resection in order to ensure that the blood supply to the bowel is not compromised.^[22] In a series from Egleston Children's Hospital in Atlanta, one third of patients required intestinal resection along with resection of the mesenteric cysts.^[8]

Omental cysts can always be removed without resecting the adjacent transverse colon or the stomach.^{[21, 22]}