Comparison between ultrasonographic and caliper measurements of testicular volume in the dog.

The aim of this study was to compare the accuracy of two methods used to clinically estimate testicular volume in the dog. Caliper and ultrasonographic measurements of testicular dimensions (length, width and height) of both testes were performed on 21 adult Beagles. Either measurement was taken in vivo over the scrotal skin and again in vitro after castration, excluding or including, when possible, the epididymis. In a sub-sample of 14 testes of 7 randomly selected dogs, the testicular volume was calculated by the formula of an ellipsoid: length (l)xwidth (w)xheight (h)x0.5236, and the empiric formula of Lambert: (l)x(w)x(h)x0.71. The calculated volumes were then compared to the actual ones, which were estimated by water displacement. For each measurement method, the formula that estimated more accurately the true testicular volume was, subsequently, applied to the calculation of the testicular volume of the remaining testes. The formula of ellipsoid estimated testicular volume more accurately when in vivo and in vitro caliper measurements and in vitro ultrasound measurements were performed. The formula of Lambert estimated testicular volume more accurately when in vivo ultrasound measurements were performed. The volumes calculated from the measurements of calipers over the scrotal skin overestimated true volumes, on average, by 69+/-27% (concordance correlation coefficient r(ccc)=0.49). By contrast, those calculated from the ultrasonography measurements were more accurate, overestimating the true volumes by 17+/-24% (rccc=0.81). Therefore, ultrasonography when the formula of Lambert is used is more accurate than caliper methods for the estimation of testicular volume in clinical practice and should be the method of choice.