Duodenal duplication cyst with profound elevation of intracystic carbohydrate antigen (CA 19-9) and carcinoembryonic antigen (CEA): a rare but important differential in the diagnosis of cystic tumours of the pancreas.

CONTEXT Enteric duplication cysts are rare lesions of uncertain incidence and natural history. Pre-operative confirmation of diagnosis can be difficult. This case reports an adult duodenal duplication cyst presenting with grossly elevated intra-lesional levels of tumour markers. CASE REPORT A 57-year-old female was found to have a complex cystic lesion of the head of the pancreas. Intra-lesional fluid analysis revealed a grossly elevated CA 19-9 and CEA. Resection was undertaken under the assumption that this was a cystic tumour. Macroscopic examination after opening the duodenum revealed a villous, circumferential tumour in the proximal duodenum measuring 4 cm in length. A cystic lesion was present in the medial wall of the tumour and did not communicate with the duodenal lumen. Microscopically, the tumour comprised Brunner's gland hyperplasia with associated mucosal thickening. The wall of the underlying cystic lesion was comprised of muscularis formed by the outer muscle coat of the duodenal wall. The final diagnosis was of a duodenal duplication cyst. There was no evidence of dysplasia or malignancy. CONCLUSION This is the first report of a duodenal duplication cyst having elevated intra-cyst fluid levels of amylase, carbohydrate antigen CA 19-9 and carcinoembryonic antigen (CEA). Although rare, this is an important differential diagnosis in the management of cystic tumours of the pancreas.