A duplication cyst, the result of multiple twinning, persistent embryologic diverticula or aberrant lumi-nal recanalisation, is a spherical or tubular structure that contains mucosa of the intestinal type and is surrounded by a layer of smooth muscle. They all have the same anatomic structure as normal bowel wall and are mostly (35%) located in the distal ileum on its mesenteric side, decreasing in frequency as one goes proximally. Sometimes there is a connection with adjoining bowel, but this exists in only a minority of cases. If they do communicate, its recognition as a tubular structure with intestinal content is more difficult. The non-communicating duplication cysts are cystic because of the mucosal secretions. The increasing number of prenatal and postnatal US examina tions means that the non-communicating duplication cysts are recognized more often (Berrocal et al. 1999). The clinical manifestation and diagnostic procedures depend on the localization and type of duplication cyst. These cysts are asymptomatic; however, they can manifest later in life because of complications. A duplication cyst can contain ectopic gastric mucosa in which bleeding can occur. Clinical symptoms are bleeding (melena and hematemesis can cause serious anemia) and intermittent abdominal pain, vomiting and sometimes a palpable mass. Obstruction, volvulus and intussusception are well known complications.
Plain film, US, contrast examination, scintigra-phy and even CT and MRI can be useful to diagnose a duplication cyst. Plain film may show obstruction. US may show the non-communicating anechoic cystic duplication cysts with the clearly visible,
characteristic bowel wall in which the mucosa is echogenic and the muscularis hypoechogenic. The muscularis is typically shared with adjacent bowel wall but the mucosal layer is separated (Fig. 5.15a). They can be multi-locular and can contain echo-genic debris because of bleeding or mucosal secretions. The contrast follow-through exam shows impression on the bowel wall and displacement of the bowel loops. In the case of communicating cysts the abnormal configuration of the bowel can be seen. CT and MRI show a cyst with an enhancing wall after contrast administration (Fig. 5.15b).
On plain film the cyst can be suspected by displacement of bowel loops and calcifications or by the signs of obstruction.
An upper GI tract examination may show displacement of bowel loops but is usually unremarkable.
On US these mostly multilocular cysts have fine septations and can be anechoic or, after bleeding or infection, filled with echogenic debris (Fig. 5.16)
CT and MRI are rarely indicated but show wall and septae enhancement after contrast injection.
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