ARRS 2022 Abstracts

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1157. Thyroid Nodule Margins in ACR TI-RADS: Adding Points for Macrolobulation is Not Useful
Authors * Denotes Presenting Author
  1. Logan Haug *; Mayo Clinic Arizona
  2. Nirvikar Dahiya; Mayo Clinic Arizona
  3. Scott Young; Mayo Clinic Arizona
  4. Maitray Patel; Mayo Clinic Arizona
Objective:
There are three main scoring systems in place for thyroid nodule evaluation: Korean TIRADS, European TIRADS, and the American College of Radiology (ACR) TI-RADS. In both the Korean and European systems, nodule margins are suspicious only if deemed microlobulated. In the ACR TI-RADS system, a lobulated margin is assigned points regardless of whether it is microlobulated or macrolobulated. We evaluated the performance of ACR TI-RADS when points for lobulated margins are applied only when the margins meet a quantified measure of margin microlobulation and not applied when nodules only demonstrate macrolobulation.

Materials and Methods:
We retrospectively reviewed ultrasound and pathology records (05/01/2018 to 07/31/2020) to find all thyroid nodules at one institution characterized as having lobulated margins using the ACR TI-RADS lexicon and subsequently undergoing FNA. Two observers reevaluated each nodule to substratify based on presence or absence of microlobulation, which was quantitatively defined as a protrusion with a base < 2.5 mm in length. The ACR TI-RADS score and classification for each nodule was determined when points were assigned for any lobulation (“any-lobulation-TI-RADS score") and when points were assigned only for microlobulation (“microlobulation-only TI-RADS score"). The impact of detection of malignant nodules and avoidance of benign FNA when margin points for lobulation were added only when microlobulated was analyzed.

Results:
Fifty-eight of 516 thyroid nodules undergoing ultrasound-guided FNA were classified as lobulated, comprising the study population. Twenty-one (36.2%) had microlobulated margins, with 12 of the 21 (57.1%) being malignant. Comparatively, of the 37 nodules showing only macrolobulated margins without microlobulation, only 2 (5.4%) were malignant (p < 0.0001). For 53 nodules at or over 10 mm, all met size criteria for pursuing FNA based on the any-lobulation-TI-RADS score, with 10 (18.9%) malignant. Of these 53 nodules at or over 10 mm in diameter, 38 met size criteria for pursuing FNA based on the microlobulation-only-TI-RADS score, still capturing the 10 (26.3%) that were malignant. All 15 of the nodules that would not have met size criteria for sampling based on the microlobulation-only-TI-RADS score were benign, representing 28.3% of the nodules at or over 10 mm that were initially classified as lobulated.

Conclusion:
Adding two points to the ACR TI-RADS score for lobulated thyroid nodules should only apply when microlobulations are present, defined as protrusions with a base < 2.5 mm in diameter.