C4-P-10Three-dimensional ultrastructural analysis of secretory granules in histological paraffin sections of endocrine tumors using low-vacuum SEM

Secretory granules of endocrine tumors are traditionally identified by transmission electron microscopy of tissue samples. Recently, we developed a simple method for three-dimensional morphological analysis of conventional paraffin sections using low-vacuum scanning electron microscopy (SEM) [ 1 ], and showed that this technique was useful for pathological diagnosis of renal biopsy samples [ 2 ]. In this study, we investigated whether this method is useful as an adjunct in pathological diagnosis of endocrine tumors. Preparations were processed according to our original method. Paraffin sections (5 μm thick) obtained from a normal rat pancreas as a control, a human pituitary adenoma and a colorectal carcinoid tumor were generated by the conventional method. After deparaffinization, the sections were stained only with platinum blue aqueous solution (TI-blue staining kit: Nisshin EM, Tokyo) for 15 min at room temperature, and then observed by low-vacuum SEM (TM-1000, TM3030 plus: Hitachi, Tokyo) at high magnification (∼30,000 ×). Under low-vacuum SEM, secretory granules of each cell could be identified as bright spherical granules in each paraffin-sectioned tissue, depending on the contrast of BSE signals. Figure shows low-vacuum SEM image (a) and TEM image (b) of endocrine secretory granules 100-260nm in diameter (arrows) in colorectal carcinoid tumor cells. Our results suggest that low-vacuum SEM of conventional paraffin sections is suitable for the pathological diagnosis of endocrine tumors.