Large omental cyst
The KUB with oral contrast reveals a large soft tissue density overlying the lower abdomen predominantly the midline and to the left. The bowel loops are displaced by it. There are no calcific densities within. (fig 1 ).
The US reveals a large cystic abdominal mass with large peripheral loculations containing internal echoes. There are in addition internal septations. (fig 2) .The appearance of the periphery being solid was ruled out by the slow movement of the dense echoes on turning the child.
The CT reveals a cystic mass with internal septations with no air or calcification or internal nodule that displaces the bowel loops, contrast CT axial shows enhancement of the walls and of the internal septae.(fig 3).
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.Omental cysts occur more frequently in childhood, and nearly 70% of them are diagnosed before the age of 30, with a peak incidence around age 15.
Omental cysts are thought to represent benign proliferations of ectopic lymphatics that lack communication with the normal lymphatics. Cysts are thought to arise from lymphatic spaces associated with the embryonic retroperitoneal lymph sac, 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.
Omental cysts are confined to the lesser or greater omentum. They can be simple or multiple, unilocular or multilocular, and they may contain hemorrhagic, serous, chylous, or infected fluid.
They may present in one of three ways.:
(a) Asymptomatic - these patients usually have a painless, slow growing abdominal mass. (b) Chronic abdominal pain - many patients present with chronic diffuse non-localised abdominal pain, which could result from traction and stretching on the peritoneum. (c) Acute abdomen in the form of intestinal obstruction (volvulus, extrinsic compression or entrapment in the pelvis) and cyst rupture, haemorrhage, or infection.
These complications occur in approximately one-third of adult patients and two-thirds of paediatric patients.
The mass may be huge, simulating ascites. 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.
The differential diagnosis includes intestinal duplication cyst; ovarian, choledochal, pancreatic, splenic, or renal cysts; hydronephrosis; cystic teratoma; hydatid cyst; and ascites.
1. Kurtz RJ, Heimann TM, Holt J: Mesenteric and retroperitoneal cysts. Ann Surg 1986 Jan; 203(1): 109-12.
2. Vanek VW, Phillips AK: Retroperitoneal, mesenteric, and omental cysts. Arch Surg 1984 Jul; 119(7): 838-42.
3. Ricketts RR: Mesenteric and omental cysts. In: Pediatric Surgery. 5th ed. 1998:1269-1275.