Korean J Radiol.  2015 Jun;16(3):560-565. 10.3348/kjr.2015.16.3.560.

Inter-Observer Variation in Ultrasound Measurement of the Volume and Diameter of Thyroid Nodules

• Choi YJ
• Baek JH
• Hong MJ
• Lee JH

• KMID: 2155525
• DOI: http://doi.org/10.3348/kjr.2015.16.3.560

Abstract

OBJECTIVE
Thyroid nodule measurement using ultrasonography (US) is widely performed in various clinical scenarios. The purpose of this study was to evaluate inter-observer variation in US measurement of the volume and maximum diameter of thyroid nodules.
MATERIALS AND METHODS
This retrospective study included 73 consecutive patients with 85 well-defined thyroid nodules greater than 1 cm in their maximum diameter. US examinations were independently performed by using standardized measurement methods, conducted by two clinically experienced thyroid radiologists. The maximum nodule diameter and nodule volume, calculated from nodule diameters using the ellipsoid formula, were obtained by each reader. Inter-observer variations in volume and maximum diameter were determined using 95% Bland-Altman limits of agreement. The degree of inter-observer variations in volumes and the maximum diameters were compared using the Student's t test, between nodules < 2 cm in maximum diameter and those with > or = 2 cm.
RESULTS
The mean inter-observer difference in measuring the nodule volume was -1.6%, in terms of percentage of the nodule volume, and the 95% limit of agreement was +/- 13.1%. For maximum nodule diameter, the mean inter-observer difference was -0.6%, in terms of percentage of the nodule diameter, and the 95% limit of agreement was +/- 7.3%. Inter-observer variation in volume was greater in nodules of < 2 cm in maximum diameter, compared to the larger nodules (p = 0.035). However, no statistically significant difference was noted between the two groups regarding maximum nodule diameters (p = 0.511).
CONCLUSION
Any differences smaller than 13.1% and 7.3% in volume and maximum diameter, respectively, measured by using US for well-defined thyroid nodules of > 1 cm should not be considered as a real change in size.

Keyword

Ultrasound; Thyroid nodule; Volume and diameter measurement

MeSH Terms

Adult
Aged
Aged, 80 and over
Female
Humans
Male
Middle Aged
Observer Variation
Organ Size/physiology
Physical Examination/*statistics & numerical data
Retrospective Studies
Thyroid Gland/pathology/*ultrasonography
Thyroid Nodule/*ultrasonography
Young Adult

Figure

• 

  Fig. 1 Thyroid nodule diameters measured by using ultrasonography (US) is shown. On transverse US image (A), width (W) and height (H) of thyroid nodule were measured to determine maximum transverse diameter. Length (L) of thyroid nodule was considered as maximum diameter seen on longitudinal US image (B).

• 

  Fig. 2 Bland-Altman plots of interobserver agreement for thyroid nodule volume and maximum diameter. Bland-Altman plots of thyroid nodule volume (A, B) and maximum diameter (C, D) with measurement data (A, C) and standardized data (i.e., measurement differences as % of nodule volume and maximum diameter) (B, D) show relationship between two observers. Difference (y-axis) between two observers is plotted against mean value (x-axis) of two readers' measurements. Solid line indicates mean difference. Top and bottom dashed lines correspond to upper and lower margins of 95% limits of agreement. With probability of 95%, differences in normalized scores of future examinations will be between upper and lower limits of agreement (mean ± variability estimate = 1.96 standard deviation [SD]).

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