Liver needle biopsies from patients with non-A, non-B chronic active hepatitis and so-called abnormal bile duct epithelium were studied with a three-dimensional method. Photographs of bile duct structures in serial sections were transferred to acrylic plates. Five bile duct lesions of a not previously described diverticular type were revealed. The diverticuli were of varying shape with a diameter of 30 to 110 μ and a length of 75 to 150μm budding from small (12 to 25μm), slightly ectatic bile ducts. The diverticular epithelium was disordered. Some cells appeared as bile duct cells, but most were larger, with rounded nuclei, prominent nucleoli and abundant eosinophilic cytoplasm, sometimes with periodic acid-Schiff-positive, diastase-resistant granules. The lesions were only partly surrounded by a basement membrane. They were all embedded in a tight mononuclear inflammatory infiltrate associated with pronounced periportal piecemeal necrosis. In two cases, a germinal center was adjacent to the epithelium.

The pathogenesis of the diverticular bile duct lesion is unknown, but the diverticuli probably represent Hering ducts and groups of periportal liver cells which have escaped the piecemeal necrosis.