Isthmic nodules have similar US and cytopathological features and tumor characteristics to non-isthmic ones

Daniela Barros, post graduate student of the Surgical Clinic Program at Ribeirão Preto Medical School, University of São Paulo (FMRP-USP). Ribeirão Preto, SP, Brasil.

The study “Are clinicopathological features of the isthmic thyroid nodule different from nodules in thyroid lobes? A single center experience”, retrospectively reviewed patients who underwent thyroidectomy between 2006-2014. Hormonal, ultrasonographic and cytopathologic features were compared between patients with isthmic (Group-1) and with lober (non-isthmic, Group-2) nodules (DELLAL, F.D., et al).

The isthmus is the smallest part of thyroid gland which connects right and left lobes. Prevalence of thyroid nodules located in isthmus was found as 4.2-6.4% (JASIM, S. et al; ZHANG, F. et al; PAPI, G. et al). The incidence of isthmic papillary thyroid cancer (PTC) ranges from 1% to 12.3% in different studies (LIM, S.T. et al; LI, G. et al). Although PTC had an indolent course, isthmic PTCs were reported to have more aggressive behaviour, including multifocality, capsular invasion, and frequently having metastasis to lymph nodes in some studies (LEE, YS. et al; WANG, J. et al).

The features of other histopathologic types of thyroid carcinomas arising from isthmus are unknown. There is no specific suggestion for diagnosis and follow-up of isthmic thyroid nodules in clinical guidelines.

Therefore, in the present study, Dellal et al. (DELLAL, F.D., et al), from Ankara (Turkey), evaluated whether thyroid nodules located in the isthmus are different from located in thyroid lobes according to their clinicopathological features. The authors concluded that isthmic nodules appear to be indolent because of having lower malignancy rate. FNAB might be required in isthmic nodules even if it has relatively small size. The surgery with limited extent or follow-up might seem to be reliable in the management of patients having isthmic nodules especially with indeterminate cytology.

A total of 2327 patients were enrolled I the present trial and assigned into two groups: with isthmic nodules (Group-1) and non-isthmic nodules (located in right or left thyroid lobes) (Group-2). Group-1 had 251 (10.8%) and Group-2 had 2076 (89.2%) subjects. Demographic features, laboratory, cytology and histopathology results were compared between groups. Furthermore, the tumour characteristics of malignant nodules such as the type, size, multifocality, vascular invasion, lymphatic invasion, capsular invasion, extrathyroidal extension, lymph node metastasis and TNM stages (EDGE, S.B. et al.), radioactive iodine (RAI) administration and RAI doses, and stimulated thyroglobuline (Tg) levels on 6^th month of malignant patients were recorded.

US-guided Fine Needle Aspiration Biopsy (FNAB) was performed by an experienced clinician by a 27 gauge needle and 20 mL volume syringe (Logic Pro200 GE US machine and 7.5 MHz probe). FNAB was carried out on all nodules with a size of 1 cm or more. Totally 260 isthmic nodules from 251 patients in Group-1 and 4433 non-isthmic nodules from 2076 patients in Group-2 were compared according to US findings, cytology and histopathology results.

The authors found that 4.8% of nodules were located in isthmus and were compatible with the literature. Almost all US features except for macrocalcification were similar in isthmic and non-isthmic nodules. When malignant nodules were subdivided into two groups as isthmic and non-isthmic, any of the malignant isthmic nodules had non-diagnostic or benign results, but 14.3% and 15.8% of non-isthmic malignant nodules had non-diagnostic and benign results, respectively. Similarly, Goldfarb and cols. found that there was no nondiagnostic result in cytology of malignant isthmic nodule in their study in which isthmic nodules were evaluated in two groups as malignant and benign (GOLDFARB, M. et al).

In the present study (DELLAL, F.D., et al), malignancy rate of isthmic nodules was significantly low compared to non-isthmic nodules (6.2 % vs 12.5%, p = 0.002). Considering all malignant nodules, the proportion of isthmic nodules was 2.8%.

In conclusion, isthmic nodules have almost similar US and cytopathological features, and tumor characteristics to non-isthmic ones. They seem to be indolent because they had lower malignancy rate compared to non-isthmic nodules. Patients with isthmic nodule and indeterminate or nondiagnostic cytology might be candidates for follow-up. Careful examination of relatively small and hypoechoic nodules in the isthmus might be required due to the possibility of malignancy.

References

JASIM, S., et al. Investigating the Effect of Thyroid Nodule Location on the Risk of Thyroid Cancer. Thyroid [online]. 2020, vol.30, no.03, pp.401-407. [viewed 16 July 2021]. https://doi.org/10.1089/thy.2019.0478. Available from: https://www.liebertpub.com/doi/10.1089/thy.2019.0478

ZHANG, F., et al. Thyroid nodule location on ultrasonography s a predictor of malignancy. Endocr Pract. [online].  2019, vol.25, no.02, pp.131-137 [viewed 16 July 2021]. https://doi.org/10.4158/EP-2018-0361. Available from: https://linkinghub.elsevier.com/retrieve/pii/S1530891X20359243

PAPI, G., et al. Nodular disease and parafollicular C-cell distribution: results from a prospective and retrospective clinico-pathological study on the thyroid isthmus. Eur J Endocrinol [online]. 2010, vol.162, no.01, pp.137-143 [viewed 16 July 2021]. https://doi.org/10.1530/EJE-09-0660. Available from: https://eje.bioscientifica.com/view/journals/eje/162/1/137.xml

LIM, S. T., et al. Correlation between surgical extent and prognosis in node-negative, early-stage papillary thyroid carcinoma originating in the isthmus. World J Surg [online]. 2016, vol.40, no.02, pp.344-349 [viewed 16 July 2021]. https://doi.org/10.1007/s00268-015-3259-2. Available from: https://link.springer.com/article/10.1007/s00268-015-3259-2

LI, G., et al. Lymph node metastasis characteristics of papillary thyroid carcinoma located in the isthmus: A single-center analysis. Medicine (Baltimore) [online]. 2017, vol.96, no.24, pp.7143 [viewed 16 July 2021]. https://doi.org/10.1097/MD.0000000000007143. Available from: https://journals.lww.com/md-journal/Fulltext/2017/06160/Lymph_node_metastasis_characteristics_of_papillary.28.aspx

LEE, Y. S., et al. Papillary carcinoma located in the thyroid isthmus. World J Surg. [online]. 2010, vol.34, no.01, pp. 36-39 [viewed 16 July 2021]. https://doi.org/10.1007/s00268-009-0298-6. Available from: https://link.springer.com/article/10.1007%2Fs00268-009-0298-6

WANG, J., et al. Evaluation of thyroid isthmusectomy as a potential treatment for papillary thyroid carcinoma limited to the isthmus: A clinical study of 73 patients. Head Neck [online]. 2016, vol.38, no.01, pp.1510-1514 [viewed 16 July 2021]. https://doi.org/10.1002/hed.24270. Available from: https://onlinelibrary.wiley.com/doi/10.1002/hed.24270

EDGE, S. B., et al. AJCC Cancer Staging Manual. In: Edge SB, Byrd DR, Compton CC, Fritz AG, Greene FL, Trotti A, eds. Thyroid cancer staging. New York: Springer-Verlag, 2010.

GOLDFARB, M., et al. Appropriate surgical procedure for dominant thyroid nodules of the isthmus 1 cm or larger. Arch Surg [online]. 2012, vol.147, no.09, pp.881-884 [viewed 16 July 2021]. https://doi.org/10.1001/archsurg.2012.728. Available from: https://jamanetwork.com/journals/jamasurgery/fullarticle/1151594

To read the article, acess

DELLAL, F.D., et al. Are clinicopathological features of the isthmic thyroid nodule different from nodules in thyroid lobes? A single center experience. Arch Endocrinol Metab. [online]. 2021, vol.65, no.03, pp.277-288 [viewed 16 July 2021]. https://doi.org/10.20945/2359-3997000000345. Available from: http://ref.scielo.org/tx7hxm

External links

Archives of Endocrinology and Metabolism – AEM: https://www.scielo.br/aem

Fatma Dilek Dellal: https://orcid.org/0000-0003-0755-4543