Invasive thyroid cancer with a 'normal' nuclear thyroid scan

Careful primary inspection and comparison of all imaging studies should be performed during initial evaluation of a thyroid nodule

Issue: September 2008

ByStephanie L. Lee, MD, PhD, ECNU

A 45-year-old woman was referred for the evaluation of a palpable neck mass and a normal I-123 thyroid scan. The patient noted a three-year history of a hoarse voice and difficulty swallowing solid foods.

Stephanie L. Lee

She was diagnosed with gastroesophageal reflux disease and esophageal stricture. An esophageal dilatation improved her dysphagia for only one to two months. When the dysphagia recurred she could not swallow solids or liquids. She was diagnosed with esophageal spasm, but a barium swallow showed an extrinsic mass (figure 1).

A CT scan of the neck revealed a 3.5 cm mass with calcification (figure 2). The mass could not be distinguished from the prevertebral musculature of the esophagus. Involvement of the right recurrent laryngeal nerve was suspected because of asymmetric medialization of the right arytenoid. A nuclear thyroid scan was performed and was interpreted as normal without hot or cold nodules (figure 3). The patient was referred to the endocrine clinic for a thyroid biopsy with a query to explain the discrepancy between the nuclear thyroid scan and CT scan.

She had no prior history of thyroid disease or head and neck radiation. Her thyroid function was normal with a TSH 1.0 uU/mL. The nuclear scan was reviewed and compared to the thyroid ultrasound scan performed in the endocrine clinic. A clear discrepancy was noted as the length of each lobe of the thyroid was approximately the same on the nuclear thyroid scan while the right lobe was measured at 6 cm and the left lobe measured 3 cm in sagittal dimension. A 3-cm hypoechoic mass with ill-defined margins, microcalcifications and intranodular hypervascular was documented by ultrasound in the inferior pole of the right thyroid lobe. No cervical adenopathy was noted. A fine needle biopsy of the nodule was consistent with papillary thyroid carcinoma.

The patient had a thyroidectomy with central (level VI) dissection. The tumor did not invade the esophagus and was peeled off without incident. Pathology revealed a 3.5-cm papillary thyroid carcinoma with invasion through the thyroid capsule into the right recurrent laryngeal nerve.

This case illustrates that the initial evaluation of a thyroid nodule should be with a high resolution ultrasound scan. Palpation is not accurate in up to 30% of patients who are felt to have a solitary palpable nodule by exam. Sixteen percent of the incorrectly identified patients will not have a thyroid nodule on ultrasound exam and 15% will have additional nonpalpable nodules greater than 1 cm on ultrasound exam.

Figure 1. Barium swallow. A smooth extrinsic compression of the esophagus is indicated by a red arrow.

Figure 2. Axial CT scan of the neck without contrast. A mass extended from the posterior aspect of the right lobe of the thyroid is indicated by a red arrow.

Figure 3. Three views of the I-123 radioactive iodine thyroid scan. Although interpreted as normal without cold or hot nodes, the inferior margin of the right lobe shows a paucity of radioisotope accumulation and suggests a cold nodule especially in the RAO view (red arrow).

There was a clear disparity between the ultrasound and nuclear thyroid scans. The ultrasound correctly identified an intrathyroidal thyroid nodule with suspicious ultrasound characteristics for malignancy (hypoechoic, indistinct margins, microcalcifications and intranodular hypervascularity).

Careful examination of the nuclear thyroid scan showed blunting of the inferior margin of the right inferior pole consistent with either an intrinsic cold nodule or an extrinsic mass (figure 3). It is important that careful primary inspection and comparison of all imaging studies should be performed during the evaluation of a palpable thyroid mass.

For more information:

Brander A, Viikinkoski P, Tuuhea J, et al. Clinical versus ultrasound examination of the thyroid gland in common clinical practice. J Clin Ultrasound. 1992;20:37-42.

Cooper DS, Doherty GM, Haugen BR, et al. The American Thyroid Association Guidelines Taskforce. Management guidelines for patients with thyroid nodules and differentiated thyroid cancer. Thyroid. 2006;16:109-142.

Marqusee E, Benson CB, Frates MC, et al. Usefulness of ultrasonography in the management of nodular thyroid disease. Ann Intern Med. 2000;133:696-700.

Tan GH, Gharib H, Reading CC. Solitary thyroid nodule. Comparison between palpation and ultrasonography. Arch Intern Med. 1995;155:2418-2423.