Scanning electron microscopy (SEM) of the human thyroid gland: a technical improvement for follicular cell observation.

SEM is a valuable tool for the examination of hollow organ free surfaces. It has been used in a few studies of human thyroid. The cell surface observation is usually limited by the presence of colloid in the follicular lumen. A technique of direct removal of the colloid has been previously proposed. It gives good morphological results. But this method needs preliminary fixation and critical point drying of thyroid samples. Antigenic properties of tissue blocks are then unsuitable for further staining. We describe a fast and easy technique for colloid removal by washing thyroid samples in a saline solution. Colloid is correctly removed from the tissue block surface prior to fixation. Apical cells are left undamaged. The exposure of thyroid blocks to ultrasound did not improve colloid removal. A post-fixative chemical drying in hexamethyldisilazane shortens processing time. We have studied the efficiency of this technique on 24 human thyroid samples obtained by surgery (normal tissue, Grave's disease, heteromultinodular goiter, toxic solitary adenoma). All specimens were observed by SEM and transmission electron microscopy in order to assess the good preservation of cell surface details. This easy technique could be used as a routine process.