Electron microscopic studies of protein plugs and pancreatic stones. Part I. Studies on the fine structure of protein plugs obtained by endoscopic cannulation of the Vaterian papilla.

To delineate the process of protein plug formation, the fine structure of protein plugs was investigated with an electron microscope and an x-ray probe microanalyser. Protein plugs were obtained by endoscopic cannulation of the papilla from four patients with calcified chronic pancreatitis (CP), four with non-calcified CP and four with suspected CP. Macroscopic observation revealed two kinds of plugs: opague, whitish plugs of irregular shape (Type I) and translucent jellylike plugs (Type II). The essential fine structure of an amorphous substance filling a reticular network composed of thin, cottony fibrils about 0.1 μ in diameter was shared by both types of plugs. The reticular network of type I plugs were accompanied by thick, smooth fibrils about 0.5 μ in diameter in addition to the cottony fibrils. In four patients, spores of gram-negative bacilli contributed, as smooth thick fibrils, to the network formation of type I plugs. Protein plug formation was considered to start from small aggregates of a loose interlacing cottony network of fibrils with some filling by an amorphous substance and degenerating epithelial cells, followed by maturation with more compact interlacing of fibrils and denser filling by the amorphous substance. Plugs grew most probably by adherence of smaller aggregates and also by layered depositions of the reticular network and amorphous substance. No calcium deposition was detected in protein plugs.