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Endocrine

E175: Size of papillary thyroid cancers do not correlate well with pre-operative thyroid ultrasound nodule size

Introduction: Pre-operative thyroid ultrasound (TUS) is the gold standard imaging modality for risk-stratifying patients with thyroid nodules. The ATA 2015 guidelines recommend thyroid lobectomy for papillary thyroid carcinoma (PTC) < 1 cm and that lobectomy may be considered for PTC >1 cm and < 4 cm. We evaluated whether pre-operative TUS will accurately predict the size of the PTC on pathology.

Methods: A single-institution retrospective analysis was performed to assess correlation between the size of thyroid nodules on pre-operative TUS to size of the cancer on pathology. Patients >18 years of age with a pre-operative TUS within one year of thyroid resection between 2017 – 2022 were included. Size comparisons were assessed using an intra-class correlation (ICC), scored 0 – 1, where 1 denotes a stronger correlation. Sub-analyses were performed based on thyroid cancer type, and further stratified by PTC size on pathology: < 1cm, 1 – 2cm, 2 – 3cm, and >3cm.

Results:

In total, 252 patients with 261 nodules were included. Overall, 191 (75.8%) patients were women with an average age of 49.7 (±16.2) years. The average maximum diameter of thyroid nodules on pre-operative TUS was 2.9 (±1.8) cm, and the average maximum diameter of thyroid cancer on pathology was 2.2 (±1.8) cm. The ICC was 0.610 (95% CI; 0.540 – 0.670) for all nodules, 0.760 (0.620 – 0.900) for follicular carcinoma, 0.830 (0.720 – 0.930) for medullary and anaplastic carcinoma, and 0.500 (0.410 – 0.590) for PTC. Ten patients with PTC had a TUS size < 1cm with a median TUS size of 0.8cm and a median pathology size of 0.9 cm (range 0.300 – 6.500; p=0.308). One-hundred and thirty-four patients had a TUS size 1-3cm with a median TUS size of 1.7cm and a median pathology size of 1.5 cm (range 0.100 – 5.000; p=0.026). Sixty-nine patients had a TUS size >3cm with a median TUS size of 4.4cm and a median pathology size of 3.1cm (0.100 – 8.400; p-value < 0.001). Thirty-two patients (46.4%) with a PTC had a nodule that was >3 cm on TUS but was < 3cm on pathology. When sub-divided by size, ICC was unable to be obtained for PTC < 1cm due to a subject variance of zero, 0.080 (-0.260 – 0.430) for PTC 1-2cm, 0.250 (-0.110 – 0.610) for PTC 2-3cm, and 0.520 (0.350 – 0.670) for PTC >3cm. In patients with PTC where the TUS nodule was >3cm, 22% underwent a lobectomy and 78% a total thyroidectomy.

Conclusions: Pre-operative TUS of all nodules overestimated size of PTC. There is poor correlation between median TUS size and median pathology size for PTC < 3cm by ICC. In our study, nearly half of PTC who had a nodule that was >3 cm on TUS, the final pathology showed PTC < 3 cm. Pre-operative decisions of total thyroidectomy vs lobectomy for TUS > 3cm should not be made by TUS size alone.

Learning Objectives:

  • demonstrate how pre-operative thyroid ultrasound characterizes thyroid nodules.
  • demonstrate the discordance between the size of thyroid nodules on ultrasound to the size of cancer on pathology.
  • understand how intra-class correlation can compare related metrics.