This article is more than 5 years old. Information may no longer be current.
The mystery of the bouncing thyroid nodule
Click Here to Manage Email Alerts
In 2005, a 67-year-old woman with hypertension was referred to the endocrine clinic for a thyroid nodule found on her first routine physical exam with her new primary care provider. She had no prior history of thyroid disease or head and neck radiation. Her family history was negative for thyroid disease or thyroid cancer. She reported no neck mass, anterior neck pressure or dysphagia.
Nodules discovered
On exam, the patient’s thyroid was mildly enlarged at 30 g, with a 1-cm nodule in the right lobe. The nodule was firm to palpation, mobile and nontender.
Stephanie L. Lee
An ultrasound was performed in the endocrine clinic that showed a mildly enlarged thyroid with multiple small thyroid nodules. The two largest nodules were a hypoechoic nodule (1.0 cm x 0.8 cm x 1.2 cm) in the posterior lower right lobe and a second hypoechoic nodule (1 cm x 0.8 cm x 0.8 cm) in the isthmus. The right and isthmus nodules had well-demarcated borders without microcalcifications or intranodular vascularity. Neither nodule was taller than wide in shape.
Ultrasound-guided fine-needle aspiration of the right lobe >1-cm nodule showed an indeterminate cytology (Bethesda 3) with a microfollicular pattern and an absence of colloid. Based on guidelines used in 2005, after an indeterminate biopsy, an I-123 thyroid scintigraphy was obtained to exclude an autonomous nodule with a very low risk of malignancy.
Nuclear thyroid scan advised
Despite a thyroid-stimulating hormone level of 1.25 mIU/L (reference range, 0.4-4), her nuclear thyroid scan showed that the dominant nodes in the right lobe and isthmus were autonomous (Figure 1).
Figure 1. Radioactive iodine thyroid scan. Four hours after the oral administration of 455 mcCi iodine-123, the thyroid scan is shown in three views: anteroposterior (AP), left anterior oblique (LAO), right anterior oblique (RAO). Two “hot” nodules are seen with increased radioiodine uptake compared with the relatively suppressed uptake in the surrounding parenchyma. One nodule is in the right lower pole, but the second nodule (white arrow) seems to ”bounce” between the right (R) and left (L) thyroid lobes.
Reprinted with permission from McDonnell. Endocrine Practice. 2006;12:599.
The 2009 American Thyroid Association guideline for thyroid nodules and cancer suggests the first step after the detection of a thyroid nodule is to measure TSH followed by a thyroid ultrasound to confirm the presence of a nodule. If the TSH is normal or elevated, an ultrasound-guided biopsy should be performed. Under this paradigm, a nuclear thyroid scan is not recommended.
However, in 2005, the guideline recommended performing a nuclear thyroid scan after an indeterminate biopsy. In fact, the nuclear scan reclassified the nodules as very low risk of malignancy. The scan showed that both nodules were autonomous with increased iodine uptake compared with the surrounding parenchyma, whose uptake was suppressed.
Figure 2. Three views of the nuclear thyroid scan and anatomic diagrams. In the AP view, the thyroid is parallel with the camera with nodule 1 (N1) in the lower right pole and nodule 2 (N2) in the isthmus. In the LAO view, the left lobe of the thyroid is rotated toward the camera with the N1 nodule in the right lower pole, and the N2 isthmus nodule is rotated away to overlap the right lobe (both nodules appear to be in the same lobe). In the RAO view, the right lobe of the thyroid is rotated closer to the camera with the N1 nodule remaining in the right lower pole, but now the N2 isthmus nodule is rotated away and overlaps the left lobe (nodules appear to be in opposite lobes).
Source: Image courtesy of Stephanie L. Lee, MD, PhD, ECNU
Bouncing nodule explained
This scan provides an important lesson on the interpretation of thyroid scans and localization of nodules within the thyroid. Four hours after an oral dose of iodine-123, a scintigraphy scan is performed with three views obtained: anteroposterior (AP), left anterior oblique (LAO) and right anterior oblique (RAO). The LAO view turns the patient such that the left lobe of the thyroid is rotated toward the camera, making the left lobe appear larger than in the AP view. The RAO view turns the patient such that the right lobe of the thyroid is rotated toward the camera, making the right lobe appear larger than in the AP view.
The first “hot” nodule is in the right inferior pole (N1) and appears in the correct anatomical positions in all three positions (AP, LAO, RAO). But the second hot nodule appears to bounce to either the right or left lobes depending on the view of the thyroid scan (Figure 2). This artifact is present because the isthmus nodule rotates in the LAO view and overlaps the right thyroid lobe, but with rotation for the RAO view, the isthmus nodule overlaps the left lobe.
Understanding the anatomical relationships in the three views in three dimensions, shows the only location that makes sense is for the second hot nodule to be located in the isthmus. Understanding the method of nuclear thyroid scanning allows the clinician to pinpoint nodules observed on ultrasound imaging.
For more information:
- Cooper DS. Thyroid. 2009;19:1167-214.
- Moon WJ. Radiology. 2008;247:762-770.
- Smith JR. Clin Nucl Med. 2004;29:181-193.
Disclosures:
- Stephanie L. Lee, MD, PhD, ECNU, is an Associate Professor of Medicine and Associate Chief, in the Section of Endocrinology, Diabetes and Nutrition at Boston Medical Center. She can be reached at Boston Medical Center, 88 E. Newton St., Endocrinology Evans 201, Boston, MA 02118; email: stephanie.lee@bmc.org. She reports no relevant financial relationships.