Adenomatoid tumors: A light microscopic, histochemical, and ultrastructural study

The histogenesis of the adenomatoid tumor has been controversial. The clinical, light microscopic, and histochemical features of six cases, with electron microscopy of three cases is presented and compared to previous studies. The histologic diagnosis rests upon recognition of one of three distinctive patterns: plexiform, tubular, or canalicular, or their various admixtures. There is a similarity of these areas with foci of malignant mesotheliomas. Acid mucopolysaccharide (AMPS), a product of both normal and neoplastic mesothelium, was histochemically present in all six cases and in the reported results of five previous studies. This material was at least partially digested by hyaluronidase. Electron microscopic features include microvilli, desmosomes, tonofilaments and tonofilament-like structures, and dilated intercellular spaces. This agrees with previous studies, which compared normal mesothelium and mesotheliomas with adenomatoid tumors, and gives further support to a mesothelial origin of these tumors.