Cancers in the thyroid isthmus are more likely to spread outside of the thyroid

CLINICAL THYROIDOLOGY FOR THE PUBLIC A publication of the American Thyroid Association

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THYROID CANCER Cancers in the thyroid isthmus are more likely to spread outside of the thyroid

BACKGROUND The thyroid gland is shaped like a butterfly with two wings or lobes on either side of the windpipe that are joined together by a bridge of tissue, called the isthmus, which crosses over the front of the windpipe. Most thyroid cancers are found in the lobes and only 2-9% of cancers are located in the isthmus. Investigators have reported that cancers in isthmus are more likely to spread outside of the thyroid. While overall prognosis of papillary thyroid cancer is good, the prognosis of patients with cancer spreading out of the thyroid is less favorable. Specific ultrasound features of nodules are suspicious of cancer like: taller-than-wide shape, an irregular margin, markedly dark appearance and microcalcifications. However, these findings are based on cancers located in the thyroid lobes and so far there are no reports on characteristics of suspicious nodules located in the isthmus. This study examined ultrasound characteristics of papillary thyroid cancer located in the isthmus as compared to cancers located in the thyroid lobes.

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THE FULL ARTICLE TITLE: Hahn SY et al. Ultrasound findings of papillary thyroid carcinoma originating in the isthmus: comparison with lobe originating papillary thyroid carcinoma. AJR Am J Roentgenol 2014;203:637-42.

SUMMARY OF THE STUDY At total of 48 patients with papillary thyroid cancer located in the isthmus and 96 patients with papillary thyroid cancer located in lobes were identified between 2007 and 2008. All the patients had undergone preoperative ultrasound of the neck, total thyroidectomy with bilateral central-lymph-node dissection and postoperative follow-up for at least 2 years.

The cancers located in the isthmus showed a higher frequency of the cancer spreading outside of the thyroid as compared with cancers located in the lobe (83% vs. 66%). Both groups showed no differences in term of other prognostic factors. Ultrasound imaging showed that cancers located in the isthmus were associated with a higher incidence of the following features than tumors located in the lobes: wider-than-tall shape (91.7% vs. 56.3%) and ultrasound findings suspicious for tumor spreading outside the thyroid (93.8% vs. 53.1%). In addition, in the group of patients with spread of the cancer to the lymph nodes, cancers located in the lobe tended to associate with lymph node spread at the same side of the cancer (84.6%), whereas patients with isthmus cancers tended to have lymph node involvement on the both sides of the neck (50%).

WHAT ARE THE IMPLICATIONS OF THIS STUDY? The results of this study suggest that papillary thyroid cancers located in the isthmus are more likely to spread outside of the thyroid than cancers located in the lobes. Because of these findings, a biopsy should be performed in all isthmus nodules with suspicious findings by ultrasound and special attention should be paid to search for abnormal lymph nodes on both sides of the neck.

—Jamshid Farahati MD

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ATA THYROID BROCHURE LINKS

Thyroid cancer: http://www.thyroid.org/cancer-of-the-thyroid-gland

Thyroid Surgery: http://thyroid.org/patients/patient_brochures/surgery.html

Thyroid Nodules: http://www.thyroid.org/what-are-thyroid-nodules

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