[Vacuolated-cell microfollicular adenoma of the thyroid]

A case of vacuolated (signet-ring) cell microfollicular adenoma of the thyroid is presented and confronted to the pertinent literature. It is a rare lesion. Its histologic aspect, featuring vacuolated cells and microfollicules, sometimes clover-shaped, and the results of the mucin stains and thyroglobulin immunostaining confirm the follicular-cell nature of the tumor and exclude primary mucin-producing tumors of the thyroid. Arrest of folliculogenesis appears to be the basic mechanism of histogenesis in our case.