Hyalinizing trabecular tumor of the thyroid: diagnosis of a rare tumor using ultrasonography, cytology, and intraoperative frozen sections

Abstract

Purpose: The goal of this study was to evaluate the clinicopathological and imaging features of thyroid nodules surgically diagnosed as hyaline trabecular tumor (HTT), and to assess the role of cytology and frozen sections (FS) in the diagnosis of HTT.

Methods: This study included 21 thyroid nodules in 21 patients treated from August 2005 to March 2015 (mean age, 53.3 years) who were either diagnosed as HTT or had HTT suggested as a possible diagnosis based on cytology, FS, or the final pathology report. Patients' medical records were retrospectively reviewed for cytopathologic results and outcomes during the course of follow-up. Sonograms were reviewed and categorized.

Results: Twelve nodules from 12 patients were surgically confirmed as HTT. Ultrasonography (US)-guided fine needle aspiration (FNA) was performed on 11 nodules, of which six (54.5%) were papillary thyroid carcinoma (PTC) or suspicious for PTC and three (27.3%) were HTT or suspicious for HTT. Intraoperative FS suggested the possibility of HTT in seven nodules, of which four (57.1%) were confirmed as HTT. US-FNA suggested the diagnosis of HTT in 10 nodules, of which three (30.0%) were confirmed as HTT. Common US features of the 12 pathologically confirmed cases of HTT were hypoechogenicity or marked hypoechogenicity (83.4%), absence of calcifications (91.7%), parallel shape (100.0%), presence of vascularity (75.0%), and probable benignity (58.3%).

Conclusion: HTT should be included in the differential diagnosis of solid tumors with hypoechogenicity or marked hypoechogenicity and otherwise benign US features that have been diagnosed as PTC through cytology.

Keywords: Biopsy, fine-needle; Frozen sections; Thyroid gland; Thyroid nodule; Ultrasonography.

Fig 1.. A 70-year-old woman was surgically diagnosed with hyaline trabecular tumor (HTT).

A. Ultrasonography (US) reveals a 40-mm hypoechoic solid mass (arrows) with relatively benign US features that was assessed as probably benign. B. Microscopy shows cells containing nuclear grooves (white arrow) and inclusions (black arrows; H&E, ×200). C, D. Immunohistochemical staining for cytokeratin 19 is negative (cytokeratin 19, ×200) (C), but membrane expression for Ki-67 is found (Ki-67, ×200) (D), confirming the diagnosis of HTT.

Fig 2.. A 49-year-old woman was surgically diagnosed with hyaline trabecular tumor.

Ultrasonography (A, transverse; B, longitudinal) shows a 15-mm solid nodule (arrows) with marked hypoechogenicity, circumscribed margins, parallel shape, and no calcifications. The final assessment of this nodule was probably benign.

Fig 3.. A 36-year-old woman for whom the possibility of hyaline trabecular tumor (HTT) was suggested by ultrasonography-guided fine needle aspiration.

A. Sonogram shows a 30-mm mainly solid, isoechoic mass (arrows) with circumscribed margins, assessed as probably benign. B. The cytology specimen reveals cells containing nuclear grooves (black arrows) and inclusions (white arrows) in an abundant hyaline background, and the possibilities of HTT and papillary thyroid carcinoma (PTC) were suggested in the diagnosis (H&E, ×400). C. Pathologic specimen obtained after surgery shows follicular cells with a papillary structure, and the tumor was confirmed as PTC, conventional type (Papanicolaou, ×200).