A case of hyalinizing trabecular tumor of the thyroid gland

Abstract

The patient was a 63-year-old man. In year X-3, neck ultrasonography (US), performed as part of a complete medical checkup, revealed a mass in the right thyroid lobe. Fine-needle aspiration (FNA) cytology was performed at the Otolaryngology department. Although papillary carcinoma could not be ruled out, the mass was classified as a class III tumor. Although neck US performed in years X-2 and X-1 showed no changes in the thyroid mass, the patient noted discomfort in the neck and requested the resection of the thyroid mass. Thus, surgery (right hemi-thyroidectomy) was performed in year X. The right hemi-thyroidectomy was conventionally performed; however, lymph node dissection was not performed because no swollen regional lymph nodes were observed. The mass was pathologically diagnosed as a hyalinizing trabecular tumor (HTT) based on hematoxylin-eosin staining and immunostaining. HTT of the thyroid is a rare tumor exhibiting peculiar features, as proposed by Carney et al. in 1987. It is a special type of tumor originating from the follicular epithelium that cytologically and histologically resembles a papillary carcinoma. While this tumor is often suspected to be a papillary carcinoma by FNA cytology, a definite diagnosis is often made based on intraoperative or postoperative pathological examination. Our case suggests that when preoperative FNA cytology reveals many intranuclear inclusions and nuclear grooves, HTT should be considered, in addition to papillary carcinoma.