Difficultés diagnostiques en cytopathologie thyroïdienne : à propos de deux cas de tumeur trabéculaire hyalinisante

Hyalinizing trabecular tumors (HTT) are very rare thyroid tumors whose diagnosis is difficult, particularly in cytology. They are frequently diagnosed as papillary carcinomas due to the cytological similarities between those two tumors (anisocariosis, intranuclear cytoplasmic inclusions, nuclear grooves and nuclear overlapping). Here, we report two HTT cases which were initially diagnosed as papillary carcinoma, on the preoperative cytology and for which the patients underwent total thyroidectomy with lymph node dissection. From these two cases and a literature review, we have searched for diagnostic criteria which could increase the sensitivity of HTT diagnosis in thin layer cytology. We have found that only the identification of the fibrillar and hyaline material within the cellular cluster of the HTT seems discriminating between both tumors, even though it is difficult to diagnose it is difficult to diagnose on thin layer cytology. One major help for the diagnosis would be the typical membranous and cytoplasmic MIB-1 immunostaining. However, no experiment has been undertaken with thin layer smears for HTT.