Optically clear nuclei in papillary carcinoma of the thyroid: Demonstration of one of the fixation artifacts and its practical usefulness

To examine whether or not optically clear nuclei are one of the fixation artifacts in papillary carcinoma of the thyroid. Experiments using an optimal immersion fixation method by making thin-sliced specimens, 5 x 2 x 2 mm in size were adopted. Fixatives tested were 10% formalin, 10% buffered formalin, mixture of alcohol and formalin (4: 1), 95% alcohol, 4% phosphate-buffered paraformaldehyde, Carnoy's fixative, Bouin's fixative and various concentrations of formalin. Tested thyroid lesions in total were: cases with papillary carcinoma (38); follicular carcinoma (one); follicular adenoma (15); adenomatous goiter (11); Hashimoto's thyroiditis (two); Grave's disease (five); and normal thyroid tissue around tumor (five). Routinely processed papillary carcinoma showed a high occurrence (64.6%) of the optically clear nuclei contrasted by a low occurrence (almost 0%) in other lesions. However, this rate in papillary carcinoma decreased (< 35.3%) in all experimental groups irrespective of the choice of fixatives. Frequent occurrence (61.9-66.6%) of the optically clear nuclei was reproduced in papillary carcinoma fixed in a higher concentration of formalin (40-60%) in the experimental groups. These results demonstrated that the optically clear nuclei are one of the fixation artifacts, although still useful as a diagnostic criterion.