[Papillary carcinoma of the thyroid: development of the histological criteria for diagnosis. Study of 29 cases and review of the literature].

Papillary carcinoma (PAP) is the most frequent malignant tumour of the thyroid. PAP and follicular carcinoma of the thyroid are two biologically different tumours, without any intermediate or mixed form. Therefore the differentiation between PAP and follicular carcinoma is essential. The histological diagnosis of PAP is based upon several criteria, the most important being the papillae, the "ground glass" nuclei, and the psammoma bodies. The value of the "ground glass" nuclei in the diagnosis of PAP has been particularly emphasized in the last 10 years. The need to take into account all the diagnostic histological criteria of PAP is necessary in the definition of the different variants of PAP, particularly its follicular variant. We report 28 cases of PAP and one case of insular carcinoma, the latter probably originating from a PAP. "Ground glass" nuclei often associated with "grooved nuclei", were identified in the paraffin sections of 7 PAP. One case was classified as a follicular variant of PAP. Psammoma-bodies were seen in 6 PAP. Eleven PAP were less than 1 cm in diameter (microPAP). One microPAP presented with important lymph node metastases and blood vessels' involvement; 2 others microPAP arose in a vesicular adenoma. Six PAP were entirely encapsulated, without any lymph node metastasis or vessel invasion. Six PAP presented with lymph node metastases associated with lymphatic and/or blood vessels invasion. Lymphatic and blood vessel invasion was seen more often in association with PAP extending to the thyroid capsule. The histological classification and prognostic criteria are discussed and compared with those previously described in the literature.