A gastrointestinal tract duplication cyst represents a congenital anomaly found anywhere along the alimentary tract, with the colon being an uncommon site and representing only 13%-30% of cases. It shares a common muscle wall and blood supply but has a separate mucosal lining. The aetiology is unclear but the duplication is thought to occur early in embryo-logical development, usually as a failure of recanalisation. These cysts are located in or adjacent to the wall of part of the gastrointestinal tract, have smooth muscle in their walls, and are lined by mucosa similar to that of some other portion of the alimentary tract. However, there may be ectopic squamous mucosa, transitional ciliated mucosa, lymphoid aggregates or ganglion cells. Gastric mucosa and pancreatic tissue
are the only ectopic tissues of clinical importance. Technetium isotope studies may help demonstrate ectopic gastric mucosa Duplications are most commonly spherical cysts but may be tubular structures that parallel the normal gut, most commonly being on the mesenteric aspect of the alimentary canal. They may or may not communicate with the enteric lumen. The colon is the least frequently involved site and there is a gradient of decreasing frequency from the caecum to the rectum. Of the large bowel duplication cysts approximately 40% are within the caecum. Their variation includes the colorectal tubular duplication cyst (duplication of the hind gut). This is a double-barreled duplication involving part or all of the large bowel with a "twin" segment on the mesen-teric or ante-mesenteric side.
Patients normally present in the neonatal period or in infancy and there is a male-to-female ratio of 1:2. The patient may present with constipation, with obstruction if the cyst is of large size, or may present with bleeding if the cyst communicates with the normal gut lumen, and if there is ulceration of gastric mucosa within the duplication cyst. Duplication cysts may be associated with recto-genital or recto-urinary fistula, duplication of the internal or external genitalia, vertebral anomalies and multi-system congenital anomaly complexes. Female patients may present with the passage of faeces through the vagina. Approximately 20% of rectal duplications communicate with the rectal lumen or may connect with the perineum as a chronic peri-anal fistula.
At contrast enema there may be simultaneous opacification of the true and the twin lumen. The cystic duplication may or may not contain air depending on whether it communicates with the lumen of the colon.
The most effective imaging is cross sectional, with ultrasound being the modality of choice although cysts may also be seen on fluoroscopy as filling defects (Fig. 6.12a). Ultrasound may show a sonolucent mass with through transmission if the cyst contains clear fluid contents, or may show an echogenic mass if the cyst contains haemorrhage or debris (Fig. 6.12b,c). Typically the inner echo-genic mucosal, and outer hypo-echoic muscle layers are seen confirming the diagnosis. CT or MRI can be used for greater clarification. MRI would be the investigation of preference given the absence of ionizing radiation and the additional information which can be obtained about the cyst contents on different sequences. The intra-cystic fluid will be of mid-signal intensity on T1-weighted MR images and may be heterogeneous; it will return a homogeneous high signal intensity on T2-weighted images.
Fig. 6.12a-c. Duplication cyst of the colon. a Contrast enema outlines the filling defect of a caecal duplication cyst. b Ultrasound of a duplication cyst at the hepatic flexure. c High resolution ultrasound in the same patient shows the layers of the cyst wall and some echogenic debris within it
Fig. 6.12a-c. Duplication cyst of the colon. a Contrast enema outlines the filling defect of a caecal duplication cyst. b Ultrasound of a duplication cyst at the hepatic flexure. c High resolution ultrasound in the same patient shows the layers of the cyst wall and some echogenic debris within it b a c
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