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Malignancy more likely for isthmus thyroid nodules vs. other locations
The location of a thyroid nodule is an independant risk factor for malignancy, with cancer most likely to develop in nodules of the isthmus vs. other portions of the thyroid, according to findings published in Thyroid.
“It is interesting to notice some variation in malignancy predisposing in different locations within the thyroid gland, suggesting potential biological differences in isthmus vs. lobar regions,” Sina Jasim, MD, MPH, assistant professor of medicine in the division of endocrinology, metabolism and lipid research in the department of internal medicine at Washington University in St. Louis School of Medicine in St. Louis, Missouri, told Healio. “The findings support the concept that thyroid tissue should not be considered homogenous and may determine not only the propensity to form nodules, but also risk of malignant transformation.”
Jasim and colleagues used the fine-needle aspiration data of 3,241 thyroid nodules from 3,313 adults (mean age, 54.2 years; 79.8% women) to determine where thyroid nodules appeared and cytology reports to determine whether they were malignant.
The isthmus contained 6% of all nodules, the middle lobe 45.7%, the lower lobe 37.3% and the upper lobe 11%.
Across all sections of the thyroid, there were 335 malignant nodules. Thyroid cancer was most likely in the isthmus (OR = 2.4; 2.4; 95% CI, 1.6-3.6), and 17.4% of nodes in that location were malignancy. It was more than twice as likely that an isthmus nodule would be malignant vs. a lower lobe nodule (OR = 2.4; 95% CI, 1.5-3.9) in fully adjusted models.
“It is not clear why thyroid nodules located in the isthmus are more likely to be cancerous,” the researchers wrote. “The findings support the concept that thyroid tissue should not be considered homogenous and may determine not only the propensity to form nodules, but also risk of malignant transformation.”
Among nodules in the upper lobe, 14.6% were malignant, and it was 80% more likely that than an upper lobe nodule would be malignant vs. a lower lobe nodule (OR = 1.8; 95% CI, 1.2-2.7). In addition, in the middle lobe, 10.2% of nodules were malignant, and it was 50% more likely that a middle lobe nodule would be malignant vs. a lower lobe nodule (OR = 1.5; 95% CI, 1.1-2).
The average size of nodules in the isthmus (15.5 mm) was less than the average size of those in the middle (P < .0001) and lower lobes (P = .0004).
The researchers concluded that thyroid cancer was independently predicted by thyroid nodule location (P = .005).
“Despite the low reported incidence, some data suggesting that thyroid cancer originating from the thyroid isthmus tends to behave more aggressively with worse prognosis compared with that originating in thyroid lobes,” Jasim said. “Papillary thyroid carcinoma in the isthmus tends to be associated with more frequent lymph node metastases and extrathyroidal extension regardless of tumor size. Therefore, thyroid nodules located in the isthmus region may need particular attention when evaluated clinically and sonographically.” – by Phil Neuffer
For more information:
Sina Jasim, MD, MPH, can be reached at s.jasim@wustl.edu.
Disclosures: The authors report no relevant financial disclosures.
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