Dimensional ultrasonographic relationship of the thyroid gland with associated anatomic landmarks in clinically normal dogs

Estimation of the size of the thyroid gland is considered to be important for diagnosis of several pathologic conditions in animals including dogs. Two-dimensional ultrasonography is used as a noninvasive simple method for determination of the size of thyroid gland. The purpose of the present study was to investigate the relationship among the dimensions of the thyroid gland with that of the associated anatomic landmarks of clinically normal dogs using ultrasonography. Ultrasonographic examinations were performed on 15 mixed breed dogs using an ultrasound scanner (MyLab30vet, Esaote, Genoa, Italy) with a linear-array transducer (Esaote LA 522, Esaote, Genoa, Italy).The maximal diameter and the length of the thyroid lobe were compared with that of the diameter of the common carotid artery and the trachea. The correlation between each thyroid parameter and the dimensions of the anatomic landmarks were assessed using linear regression analysis and Pearson's correlation coefficient test. According to the results, a significant linear correlation was observed between the maximum diameter of the thyroid lobe and the diameter of common carotid artery (P = 0.02, Pearson's correlation coefficient = 0.188). The coefficient of determinations (R²) for the maximum diameter of the thyroid lobe with that of common carotid artery diameter was 0.367, indicating that the strengths of the association were weak. The mean ratio between the maximum thyroid lobe diameter and the common carotid artery diameter was 1.74 ± 0.40 (range 1.11 - 2.43). However, there was no significant dimensional relationship with other selected anatomic landmarks. On the basis of the data obtained in this study, calculating the ratio between the maximum thyroid lobe diameter and the diameter of common carotid artery by using two-dimensional ultrasonography will be a useful and simple method for evaluating the size of the thyroid gland in dogs in clinical practice