Endocrine Abstracts

Objective: This study aimed to compare US features and K-TIRADS categories for diagnosing isthmic and lobar PTCs.

Methods: From January 2009 to December 2012, 163 patients who underwent thyroid surgery and were confirmed with a postoperative histopathological diagnosis of isthmic PTC were retrospectively included. Fifty-nine patients were excluded because their tumor size was < 0.5 cm, lack of preoperative thyroid US images, poor US image quality, and uncertainty between US findings and histopathological results. Eventually, 104 patients with isthmic PTC (88 female and 16 male; age range, 25–75 years; mean ± SD, 46.9 ± 9.9 years) were included in the study group. The control group comprised of 145 patients (127 female and 18 male; age range, 29–86 years; mean ± SD, 48.4 ± 10.9 years) who underwent thyroid surgery from January to April 2013 for a classic type of PTC, with the largest diameter being ≥ 0.5 cm and located in the thyroid lobe. A single radiologist retrospectively reviewed the US features and K-TIRADS categories of each nodule using a picture archiving and communication system.

Results: Most cases of isthmic (95.2%; 99/104) and lobar PTC (96.6%; 140/145) belonged to K-TIRADS category 5. Of the 104 patients with isthmic PTC, 95 and 9 cases were that of primary and non-primary cancers, respectively, whereas all 145 patients with lobar PTC had primary cancers. Isthmic PTC showed a lower prevalence of non-parallel orientation than lobar PTC (23.1 and 71%, respectively), whereas both isthmic and lobar PTC showed a high prevalence of microcalcification (69.2 and 79.3%, respectively) or irregular (spiculated/microlobulated) margin (93.3 and 95.2%, respectively). Nodule orientation was the only US feature statistically different between the two groups (P < 0.0001). There was no significant difference in patient age, sex, nodule size, composition, echogenicity, microcalcification, irregular(spiculated/microlobulated) margin, and K-TIRADS category (P > 0.05).

Conclusions: Most cases of isthmic and lobar PTC belong to K-TIRADS category 5, and only the nodule orientation parameter was different between isthmic and lobar PTC. Therefore, K-TIRADS may be useful in the diagnosis of both isthmic and lobar PTC.