Endocrine Abstracts

Aim: Although thyroid nodules located in isthmus were less frequent, papillary thyroid cancer in this location was reported to be more aggressive in some studies. Our aim was to evaluate hormonal, ultrasonographic, and cytopathologic features of nodules located in isthmus (isthmic nodules).

Material and methods: Data of patients who underwent thyroidectomy between 2006–2014 were reviewed retrospectively. Hormonal, ultrasonographic, and cytopathologic features of patients with isthmic and with lober (non-isthmic) nodules were compared.

Results: Patients with isthmic nodules (Group-1) and non-isthmic nodules (Group-2) consisted of 260 and 2171 patients, respectively. Age and gender distributions were similar. AntiTg positivity was higher in Group-1 (28.6% vs 21.2%; P=0.018). Subsequently, 268 isthmic (10.7%) and 5347 non-isthmic (89.3%) nodules were compared. Although ultrasonographical features such as presence of microcalcification and halo, nodule diameters, echogenicity, texture, margin, and vascularity were similar between groups, macrocalcification rate was lower in isthmic nodules (19% vs 27%; P=0.004). Furthermore, cytologic results were also similar. However, malignancy rate was lower in isthmic nodules (6.0% vs 11.4%; P=0.006), type of thyroid cancer was similar in isthmic and non-isthmic nodules. When malign isthmic (n=16, 2.6%) and malign non-isthmic nodules (n=605, 97.4%) were compared, diameter and type of tumor, lymphovascular and capsular invasion, extrathyroidal extension and multifocality rates were statistically insignificant. Malign isthmic nodules (n=16, 6%) had smaller size [10.05(4.00–34.50)mm vs 20.05(8.40–74.10)mm; P=0.002], higher hypoechogenity (31.2% vs 5.6%, P<0.001) and exophyticity rates (28.6% vs 4.9%; P=0.007) compared to benign isthmic nodules (n=251, 94%).

Conclusion: Although isthmic nodules had lower malignancy rate compared to non-isthmic ones, histopathologic features were similar in isthmic and non-isthmic nodules. Relatively small, hypoechoic, and exophytic nodules located in isthmus should be evaluated immediately for malignancy.