Mesenteric Cysts
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Direct answer
Among the rarest of abdominal masses, mesenteric cysts are thin-walled fluid lesions within the mesentery — the majority of lymphatic (chylous) origin, the cystic lymphangioma being the paediatric extreme — presenting either as an incidental mass or with chronic vague abdominal pain, and acutely with torsion, rupture or haemorrhage into the cyst. The physical sign textbooks quote is free mobility of a rounded abdominal mass in the transverse direction, at right angles to the line of its mesenteric attachment, because the mesentery permits swing across the abdomen but not along its root. Ultrasound followed by CT defines a thin-walled, fluid-density lesion separate from solid organs; septations suggest lymphatic origin. Complete surgical excision is the treatment — aspiration or marsupialisation recur; enucleation suits most cysts, bowel resection is needed when the cyst is inseparable from the bowel wall, and laparoscopic excision is now standard for accessible small lesions.
What you must remember
- Rarity and origin: an incidence near one per 100,000 admissions; most arise from lymphatic obstruction or congenital rests, so chylous or serous fluid is found on analysis; enteric duplication cysts and non-pancreatic pseudocysts complete the classification.
- The mobility sign: the cyst moves freely sideways (transverse plane) but not craniocaudally along the mesenteric axis — a bedside observation examiners still ask you to explain.
- Age distribution: cystic lymphangioma typically in children (soft, huge, multilocular); simple mesenteric cysts more often in adults; both sexes equally.
- Clinical patterns: silent mass found incidentally; chronic recurrent colicky pain with distension; and the acute abdomen from torsion of the cyst-loaded mesentery, rupture, haemorrhage or infection — an emergency that can mimic appendicitis or obstruction.
- Imaging: ultrasound as the first test (thin-walled anechoic or septated cyst), CT to map location, size, relation to mesenteric vessels and exclude solid neoplasm or ovarian pathology — a woman with a cystic mass always needs ovarian origin excluded first.
- Treatment rule: complete excision, ideally intact — enucleation for loose cysts, segmental bowel resection with anastomosis when the bowel wall is invested, and laparoscopic excision for suitable small cysts; aspiration and marsupialisation alone recur and are abandoned.
- Malignancy note: the vast majority are benign; rare cystic lymphangiomas harbour lymphatic malignancy or become infected — send every excised cyst for histology.
A typical exam case
A 26-year-old man presents with two years of intermittent periumbilical colic and a fullness he can feel himself. Examination finds a soft, non-tender, rounded mass about 10 centimetres across in the central abdomen that shifts easily from right to left but barely moves up and down. Ultrasound shows a thin-walled cystic lesion with a few internal septa; CT locates it in the small bowel mesentery, displacing loops, separate from pancreas, kidney and ovary-equivalent structures. At laparoscopy, a chylous cyst is peeled off the mesenteric leaves between the vessels; one segment where the wall is inseparable from the ileum requires a small bowel resection with stapled anastomosis. He is home in three days, histology confirms lymphangioma, and he remains well. Had he instead arrived with sudden severe pain and vomiting, torsion or haemorrhage into the cyst would lead the differential and surgery would proceed through the same principles — complete excision, protecting the mesenteric vasculature — but as an emergency.
Where students slip
Examiners exploit the differential of cystic abdominal masses: in a woman, ovarian cyst tops the list and must be excluded before labelling any mesenteric cyst; in children, cystic lymphangioma versus enteric duplication cyst — duplication cysts have a gut-wall layered structure on ultrasound and often bleed. The second trap is treatment: "aspiration" and "marsupialisation" are historical answers that score poorly because recurrence is near-universal — complete excision with or without bowel resection is the expected reply. Third, the mobility direction — sideways free, vertical limited — is a short-answer favourite that students reverse, and viva examiners notice.
Frequently asked questions
What is the characteristic mobility of a mesenteric cyst?
Free movement in the transverse plane across the abdomen, with restricted mobility along the long axis, because the cyst is suspended on its mesenteric pedicle.
What is the origin of most mesenteric cysts?
Lymphatic — from obstructed or congenitally sequestered lymphatic channels, producing chylous or serous content; cystic lymphangioma is the multilocular paediatric form.
Why is aspiration not adequate treatment?
Simple aspiration or marsupialisation leaves the cyst wall behind, so fluid reaccumulates and recurrence is nearly universal; complete excision is the standard.
How do mesenteric cysts present acutely?
With torsion of the mesentery, rupture, haemorrhage into the cyst or infection — sudden pain, vomiting and peritonism mimicking appendicitis or bowel obstruction.
When does excision require bowel resection?
When the cyst wall is inseparable from the bowel wall or its mesenteric blood supply — the involved segment is resected with primary anastomosis to ensure complete removal.