Smooth muscle hamartoma of the abomasum in a calf.

This report describes a case of smooth muscle hamartoma of the abomasum in a 6-month-old steer humanely killed because of severe pneumonia. At necropsy, marked thickening of the abomasal wall in the area of the pylorus was found. On cut section, the thickness of the submucosal layer, extending from the submucosa to the muscularis propria, was seen to be increased to 3 cm. The upper (i.e., nearest to the gut lumen) half of the sectioned thickening was composed mainly of adipose-like tissue and the lower half mainly of muscle-like tissue. Histologically, the submucosal layer was composed of fibroadipose tissue, within which were embedded, to varying degrees, numerous well-defined, haphazardly oriented, thin to thick bundles of smooth muscle fibres. This appears to be the first report of smooth muscle hamartoma of the stomach or abomasum in animals, including man.