BACKGROUND

Hyalinizing trabecular tumors of the thyroid (HTT) is a rare entity. Most behave as benign neoplasms, but their cytological features are challenging and can be similar to those of papillary thyroid carcinoma (PTC). The aim of this study was to compare the ultrasonography (US) readings of HTT with the cytology and frozen section readings.

METHODS

We retrospectively analyzed the US and cytology features in 10 patients (mean age, 47.5 years, range 26-81; M:F, 1:9) seen between March 2006 and November 2009 who had a histopathological diagnosis of HTT. The US findings were categorized according to the size, shape, margin, echogenicity, echotexture, presence of hypoechoic halo, and microcalcifications. Preoperative fine-needle aspiration cytology, frozen section results, and surgical treatment were reviewed. US features of HTT were compared with those of other tumors including follicular adenomas, follicular variant of PTCs, and conventional PTC.

RESULTS

Out of the 10 patients in our series, 7 underwent total thyroidectomy, and 3 had lobectomy. The sizes of the HTTs ranged from 0.6 to 4.2 cm (mean, 1.77 cm). The most common US features were solid texture (10/10), oval to round shape (10/10), a well-defined aspect (10/10), hypoechoic character (8/10), heterogeneous character (7/10), the presence of a hypoechoic halo (8/10), and no microcalcifications (10/10). The US diagnosis was indeterminate in all but one case and that was read as a benign lesion. As far as the shape and margin US features were concerned, HTT was considered to be most similar to follicular adenomas and follicular variant of PTC, but not to classical PTC. The cytology reading was PTC in 6 of 10 cases, suspicious for PTC in 2, and a HTT versus PTC in 2. The histological diagnosis of frozen sections, when performed, was PTC in three, HTT in three, medullary thyroid carcinoma in two, and deferred in one.

CONCLUSION

HTT often appears similar to follicular neoplasm on US, but it can be misjudged on cytology as PTC, even in frozen sections. HTT should be included in the list of discordant US-cytology readings of thyroid tumors. This rare tumor might be suspected more often preoperatively by careful attention to cytology in the context of the US reading.