[Ultrastructure of osteoid islets in mixed-type hepatoblastoma]

Composite morphological studies established that "osteoid" may consist of various portions of finely granular nonparticular basic substance and fibrous structures resembling collagen fibers and randomly interwoven in different directions. This substance was found to be synthesized by myoepithelial-like cells contacting by desmosomes and desmosome-like contacts and having in their cytoplasm abundant bundles of microfibrils, developed granular endoplasmic reticulum, and Golgi zones. The regularities of histotopographic location of such islets suggest that polygonal cells of forming bile ducts subject to cataplasia participate in the synthesis of intercellular "osteoid-like" substance. The similarity between hepatoblastoma of the mixed type and pleomorphic adenoma of the salivary gland is indicated.