[Hyalinizing trabecular adenoma of the thyroid].

We experienced a very rare case of hyalinizing trabecular adenoma of the thyroid. The histopathological features of this case included the following. 1) In puncture-aspiration cytodiagnosis, tumor cells aggregated around pink-stained hyaline acellular areas in an ellipsoidal or spindly configuration, with a part of the cytoplasm appearing as filamentous with unclear borders. In addition, a large number of intranuclear "holes" and nuclear grooves were evident. 2) In biopsy, tumor cells appeared in ellipsoidal or spindly configuration, with cytoplasm that easily stained with thyroglobulin but did not stain with calcitonin. The nuclei were irregular in size and some of the nuclei appeared strongly atypical, occasionally seen with cytoplastic inclusion body in the nucleus. These cells showed funicular structures in a radical arrangement with a hyaline material at the center. The hyaline material was stained positively with PAS or Laminin, but not with Cong red.