Abstract
Congenital anomalies of the alimentary tract are rare lesions in laboratory animals. We describe a congenital cyst attached to the greater curvature of the forestomach in a B6C3F1 mouse. The inner surface of the cyst was mostly covered with cuboidal or pseudostratified ciliated epithelium and was focally covered with the flat cuboidal epithelium. The base of the cyst appeared to be inserted between the layers of the outer longitudinal muscle layer of the forestomach, although no smooth muscle layer was evident in the free surface of the cyst wall. The cyst resembled duplication of the alimentary tract, as it was lined with ciliated epithelium and had developed at the greater curvature of the forestomach. Since the smooth muscle layer did not completely cover the whole wall and the cyst did not communicate with the gastric lumen, the cyst was not thought to be a standard duplication but rather a simple congenital cyst.