Tuesday, October 4, 2011

Post-Thyroidectomy Ultrasound in Patients with Differentiated Thyroid Cancer

The European Thyroid Association, the National Comprehensive Cancer Network, and the American Thyroid Association have similar recommendations for management of patients with differentiated thyroid cancer after thyroidectomy.

The guidelines recommend serial serum thyroglobulin levels and neck ultrasound as primary tests to diagnose recurrences, with diagnostic whole body radioiodine scans reserved for follow-up of patients with intermediate or high risk of persistent disease. Low-risk patients following radioiodine ablation don't seem to benefit from diagnostic whole body radioiodine scans due to the low sensitivity of these scans.

Neck ultrasound, on the other hand, is highly sensitive in the detection of cervical metastases in patients with differentiated thyroid cancer. The American Thyroid Association (2010) recommends neck ultrasound to evaluate the thyroid bed and cervical nodal compartments (see below) initially at 6 and 12 months and then annually for at least 3–5 years, depending on the patient's thyroglobulin status and risk for recurrent disease.

Stratification of patients is done after initial surgery and remnant ablationas.
  • Low-risk: There are no local or distant metastases, all macroscopic tumor has been resected, there is no tumor invasion of locoregional tissues or structures, the tumor does not have aggressive histology or vascular invasion, and no 131I uptake is seen outside the thyroid bed on the first posttreatment wholebody radioiodine scan (if 131I was given).
  • Intermediate-risk: There was microscopic invasion of tumor into the perithyroidal soft tissues at initial surgery or the tumor had aggressive histology or vascular invasion.
  • High-risk patients: There was macroscopic tumor invasion, incomplete tumor resection, distant metastases, or 131I uptake outside the thyroid bed on the post-treatment scan.


The entire neck is imaged using a high-frequency (8 MHz to 12 MHz) linear transducer. Larger patients may benefit from additional scans using a 6-MHz linear transducer. A curved or sector array transducer is then used to image the supraclavicular area. Color Doppler can be used to differentiate small lymph nodes from vessels and to help identify the vascular hilum of lymph nodes.

The thyroid bed and the nodal compartments of the neck must be meticulously scanned. The neck is divided into central and lateral compartments. The central compartment contains the resection bed, as well as the paratracheal and paraesophageal nodal chain and level I (submental and submandibular) lymph nodes. The lateral margins of the central compartment are defined by the carotid sheath.

The lateral compartments contains levels II, III, IV, and V (superior, middle, and inferior jugular, cervical and supraclavicular lymph nodes. The trapezoid muscles determine the lateral margins of the lateral compartments, and the subclavian veins determine their inferior margin.

What to Expect

Scanning can be tedious. The postoperative thyroid bed should appear as a narrow area of increased echogenicity between the common carotid artery laterally and the trachea medially.

Cervical lymph nodes are commonly seen in the lateral compartments and can present a diagnostic challenge (see below).

Local Recurrence

Any focal mass should raise concern for recurrence in the thyroid bed. Shin and colleagues compared the ultrasound appearance of recurrent and non-recurrent lesions in the resection bed and found that "the distinction between recurrent thyroid cancer and nonrecurrent benign lesions cannot be made on the basis of the sonographic features."

Benign lesions such as nodular thyroid remnants, postoperative scar, suture granuloma, muscle tissue, and fat necrosis can mimic malignancy. However, anechoic lesions seem to correspond to benignity and microcalcifications and cystic areas within a mass should raise concern for malignancy.

The images above are from four patients with differentiated papillary thyroid cancer. The top row shows the appearance of a normal resection bed, with the trachea (Tr), common carotid artery (C), the internal jugular vein (IJ), and the normal echogenic resection bed (pink arrow). The bottom row shows lesions in the resection bed (green arrows). The lesion in the left panel (L) was recurrent disease, while a similar lesion in the right panel was benign, underscoring the difficulty in differentiating benign from malignant lesions in the resection bed.

Lymph Nodes

Lymph nodes with cystic areas or punctate calcifications are highly (100% in one study) specific for metastatic thyroid cancer. Unfortunately, these findings are not very common and not very sensitive (between 10% and 50%).

The other usual techniques for differentiating benign from malignant lymph nodes are not reliable. Size does not seem to be helpful in differentiating benign from malignant lymph nodes. Round shape and loss of the echogenic hilum and hypoechoic cortex by themselves are also not specific for malignancy, especially since the echogenic hilum can be difficult to see in smaller lymph nodes.

When in doubt, fine needle aspiration is the most conservative approach.


  • Cooper DS, Doherty GM, Haugen BR, Kloos RT, Lee SL, Mandel SJ, Mazzaferri EL, McIver B, Pacini F, Schlumberger M, Sherman SI, Steward DL, Tuttle RM. Revised American Thyroid Association management guidelines for patients with thyroid nodules and differentiated thyroid cancer. American Thyroid Association (ATA) Guidelines Taskforce on Thyroid Nodules and Differentiated Thyroid Cancer, Thyroid. 2009 Nov;19(11):1167-214.
  • Sheth S, Hamper UM. Role of sonography after total thyroidectomy for thyroid cancer. Ultrasound Q. 2008 Sep;24(3):147-54.
  • Shin JH, Han BK, Ko EY, Kang SS. Sonographic findings in the surgical bed after thyroidectomy: comparison of recurrent tumors and nonrecurrent lesions. J Ultrasound Med. 2007 Oct;26(10):1359-66.

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