Mesenteric Cyst

A mesenteric cyst is a cystic mass within the mesentery of the small bowel or colon, or in the retroperitoneum. It is rare, with an incidence of about 1 in 100,000 adults and 1 in 20,000 children. It may arise at any age, with a median in the fifth decade in adults. The ileal mesentery is the most frequent site (about 60%), followed by the colonic mesentery.

Classification by origin

• Lymphatic (the most common, including simple lymphatic cysts and lymphangioma)
• Mesothelial (simple or benign cystic mesothelioma, which can recur)
• Enteric (enteric cysts and duplication cysts)
• Urogenital remnants
• Mature cystic teratoma
• Nonpancreatic pseudocysts (traumatic, infective)

Cysts are usually unilocular with clear, serous or chylous fluid, and the wall may contain epithelium, endothelium or mesothelium. Malignant transformation is under 3%, and is more frequent with cystic mesothelioma and teratoma.

Complications

• Small bowel obstruction from compression
• Volvulus and torsion of the cyst
• Infection and abscess
• Hemorrhage into the cyst
• Rupture with chylous ascites
• Rarely, vascular compression

• Often found incidentally on imaging
• Vague abdominal pain, fullness or distension, nausea and constipation
• A smooth, round, mobile abdominal mass that moves at right angles to the mesenteric attachment (mobile in the transverse plane but not along the root)
• Acute abdomen from torsion, hemorrhage, rupture or obstruction
• Children: abdominal swelling or an acute abdomen
• Red flags: peritonitis, obstruction, hemodynamic instability, a solid component or septations (neoplasm), and ascites

1. Ultrasound: a thin-walled, anechoic cyst, with or without septa, debris or fluid-fluid levels.
2. CT with intravenous contrast: a well-defined, thin-walled, fluid-attenuation mass (0 to 20 HU, or fat attenuation in chylous cysts) within the mesentery, with displacement of bowel loops and no enhancement of the content.
3. MRI: better characterization of content (high T2 signal, with variable T1 signal) and the septa.
4. Fine-needle aspiration is avoided, since it risks spillage and infection, and gives little help.
5. Tumor markers and amylase only if a neoplasm or pseudocyst is suspected.

Differentials: pancreatic pseudocyst, ovarian cyst, omental cyst, lymphangioma, mesenteric lymphadenopathy, gastrointestinal stromal tumor, cystic mesothelioma, hydatid cyst, sarcoma, aneurysm.

1. Asymptomatic cysts under 5 cm with simple features: observation with ultrasound at 6 months, then annually.
2. Symptomatic or enlarging cysts: complete excision by laparoscopy or laparotomy. Enucleation is feasible when the cyst separates from the mesenteric vessels. When the cyst is intimately adherent to the bowel blood supply, resection with the adjacent bowel and primary anastomosis is required.
3. Technique: careful dissection along the cyst wall, preservation of the mesenteric arcade, and aspiration of the content only after isolating the cyst. Cefazolin 2 g IV with metronidazole 500 mg IV before incision (children: cefazolin 30 mg/kg and metronidazole 7.5 mg/kg).
4. Complicated cysts: urgent surgery for torsion, hemorrhage or obstruction.
5. Marsupialization or simple drainage gives recurrence rates of over 25% and is used only in unfit patients.
6. Postoperative care: early feeding, analgesia with paracetamol 1 g orally every 6 hours, enoxaparin 40 mg SC daily for 5 to 7 days in higher-risk patients, and histology review for malignancy.

Outcomes: recurrence after complete excision is under 5%. Follow-up with ultrasound at 6 and 12 months. Counsel on symptoms of obstruction.