Foregut cyst of the oesophageal wall in a cynomolgus monkey (Macaca fascicularis)

Congenital oesophageal cysts of foregut origin are rare in animals and human beings. This report describes a case in a 4-year-old cynomolgus monkey with no clinical symptoms. The cyst, which was located within the oesophageal submucosal tissue near the mid-point of the oesophagus, was lined with pseudostratified ciliated epithelium and had a thin layer of submucosal tissue. The cyst was surrounded by a smooth muscle layer which was partly intermingled with the circular muscle layer of the oesophagus. The muscularis mucosae of the oesophagus was not shared with the cyst wall. Simple tubular glands were present, opening into the cyst lumen. No communication between the cyst lumen and the oesophagus was observed. Cartilaginous tissue, which is a diagnostic feature of bronchogenic cysts, was not identified in the cyst wall. On the basis of the histopathological features, a foregut cyst of the oesophagus was diagnosed.