A mathematical formula to estimate in vivo thyroid volume from two-dimensional ultrasonography.
BACKGROUND
The determination of thyroid volume (TV) is required for the management of thyroid diseases. Since two-dimensional ultrasonography (2D-US) has become the accepted method for the assessment of TV (2D-US-TV), we verified whether it accurately assesses postsurgical measured TV (PS-TV).


METHODS
In 92 patients who underwent total thyroidectomy by conventional cervicotomy, 2D-US-TV obtained by the ellipsoid volume formula was compared to PS-TV, determined by the Archimedes' principle.


RESULTS
Mean 2D-US-TV (23.9 +/- 14.8 mL) was significantly lower than mean PS-TV (33.4 +/- 20.1 mL). Underestimation was observed in 77% of cases, and it was related to gland multinodularity and/or nodular involvement of the isthmus, while 2D-US-TV matched the PS-TV in the remaining 21 cases (23%). A mathematical formula, to estimate PS-TV from US-TV, was derived using a linear model (Calculated-TV = [1.24 x 2D-US-TV]+ 3.66). Calculated-TV (mean value 33.4 +/- 18.3 mL) significantly (p < 0.01) increased from 21 (23%) to 31 (34%) of the cases that matched PS-TV. In addition, it significantly (p < 0.01) decreased from 77% to 27% the percentage of cases where PS-TV was underestimated as well as the range of the disagreement from 245% to 92%.


CONCLUSIONS
This study shows that 2D-US does not provide an accurate estimation of TV and suggests that it can be improved by a mathematical model different from the ellipsoid model. If confirmed in prospective studies, this may contribute to a more appropriate management of thyroid diseases.
Trimboli
Pierpaolo
P
Department of Experimental Medicine, Sapienza University of Rome, Viale del Policlinico 155, Rome, Italy.
Ruggieri
Massimo
M
Fumarola
Angela
A
D'Alò
Michele
M
Straniero
Andrea
A
Maiuolo
Amelia
A
Ulisse
Salvatore
S
D'Armiento
Massimino
M
D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D013961:Thyroid Gland / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D013965:Thyroidectomy; D014463:Ultrasonography