The thyroid nodule ultrasonic characteristic referred to as "Taller-than-Wide" (TtW) is defined as a nodule's anterior-posterior diameter/left-right diameter ratio (i. e. AP/LR ratio) on transverse view. This characteristic is regarded as a major feature suggesting malignancy. On the Amer College of Radiology's TIRADS ("Thyroid Imaging Reporting and Data System") guidelines, TtW status usually indicates the need for an aspiration biopsy (FNA). Given this importance, and the subjective and technical limitations of ultrasonic linear measurements of nodule diameters, it would be prudent to be aware of the probabilities that an AP/LR ratio may be under-estimated or over-estimated, potentially causing a false-negative or false-positive TtW interpretation, respectively. To assess these probabilities two approaches were taken. Eight observers were trained how to carefully measure the AP and LR diameters of thyroid nodules by ultrasound. The observers measured these diameters on the same transverse image from each of 34 benign thyroid nodules without knowledge of the measurements obtained by other observers. Thus, 272 independently obtained, rank-ordered individual AP/LR ratios (34 nodules×8 observations each) were plotted on the y-axis against themean AP/LR for each nodule (34mean AP/LRs, regarded as the consensus "true" AP/LRs for the corresponding nodule). By Spearman's rank correlation method, variations in individual AP/LR ratios (i. e., the individualAP/LR ratios minus their correspondingmean AP/LR ratios) were plotted on the x-axis as a function of their rank-ordered fraction of the total population on the y-axis. By this method, the top 20% ofindividual AP/LR ratios were 0. 075 to 0.550 greater than their correspondingmean AP/LRs. The bottom 20% ofindividual AP/LR ratios were 0. 085 to 0.300 lower than their correspondingmean AP/LR ratios. To determine the clinical significance of these variations, theindividual AP/LR rations of the 34 nodules were plotted on the y-axis as a function of their correspondingmean AP/LR ratios. Of the 28 nodules whosemean AP/LR ratios were <1, 31 (13.8%) of the 224 associated individual AP/LR ratios (28×8) were read as >1 (False Pos TtW status). Of the 6 nodules whosemean AP/LR ratios were >1, 6 (12.5%) of their 48individualAP/LR ratios (6×8) were read as <1 (False Neg TtW status). In conclusion, although interpretive deviations in the AP/LR ratio are common and frequently large, their clinical consequences in terms of generating false positive and false negative attributions of Taller-than-Wide nodular status are fortunately much less frequent (13.8% and 12.5%, respectively). None of the authors have any relevant disclosures. Presentation: No date and time listed
Though not a reliable indicator of malignancy, ultrasonic monitoring of nodule growth still has a role in the evaluation of nodules, e.g. indicating when a nodule may require biopsy or re-biopsy. Observer and technical limitations, however, limit the precision of ultrasonic determination of simple growth, vs. stability or shrinkage. Ultrasonic parameters used for this purpose all have their own limitations. Monitoring nodule growth by VOL frequently exhibits wide and conflicting swings in apparent size compared to the penultimate size, doubtlessly reflecting measurement limitations. As a growth parameter, LD typically exhibits a smoother time course but does not address growth in the other two dimensions. SUM3D includes changes in all dimensions but, like LD, is not a true measure of nodule mass or volume. This study was to determine the relative error of these three growth parameters and how it relates to their relative efficacy for nodular growth monitoring. The anterior-posterior (AP), left-right (LR) and superior-inferior (SI) dimensions of 34 benign nodules were determined ultrasonographically by four pairs of trained observers. One observer of a pair was regarded as a Time-1 observer and the other as a Time-2 observer, simulating the process for determining growth change over time. All observers measured the same image of each of the 34 nodules but were unaware of the measurements obtained by any other observer. For each image for each pair of observers, the dimensions were used to calculate the VOL, LD and SUM3D and the perceived changes thereof from Time-1 to Time-2. Since only one image for each nodule was distributed, differences between the Time-1 vs Time-2 measurements for each nodule could only reflect observer-based differences. “S”-curves plotting the nominal %-change in a parameter reported by the Time-2 observer compared to that reported by the Time-1 observer (x-axis) were rank-ordered from negative to positive changes (y-axis). The %-change in each parameter due to observer/technical error ranging from the highest over-estimate to the lowest were, in order from Top 10%, Middle 40%, and Bottom 10%, respectively: LD: 19-36%, -4 to 6%, -15 to -42%; SUM3D: 15 to 28%, -4 to 4%, -11 to -43%; VOL: 48 to 105%, -13 to 15%, -33 to -81%. The magnitude of %-change from Time-1 to Time-2 for the VOL parameter were 2 to 3 times greater than that of the LD or SUM3D parameters for the top 10% of values, the middle 40% of values, and the bottom 10% of values. These degrees of difference coincide with the wide variability seen in nodular growth curves [not illustrated here] when nodular VOL (y-axis) is plotted as a function of length of observation (x-axis). This study helps explain why monitoring nodular growth by LD or by the SUM3D usually provides a clearer, less fluctuant illustration of thyroid nodule growth over time than does VOL.
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