Ultrasonography of histologically normal parathyroid glands and thyroid lobules in normocalcemic dogs.

The purpose of this study is to characterize the sonographic appearance of canine parathyroid glands using high-resolution ultrasonography. Ten cadaver dogs were studied after euthanasia for reasons not relating to the parathyroid. The cervical region was examined using a 13-5 MHz linear transducer in right and left recumbency. Ultrasonographic features of the parathyroid and thyroid glands were compared with the gross and histopathologic findings. Thirty-five structures were identified sonographically as parathyroid glands but only 26 of 35 glands (74% positive predictive value) were proven to be normal parathyroid glands histopathologically. Of the nine false positives, five (14%) were proven to be lobular thyroid tissue. The remaining four (11%) structures were visible grossly or found histopathologically. There were no statistical differences between ultrasonographic and gross measurements of the parathyroid glands. The average size as seen sonographically was 3.3 x 2.2 x 1.7 mm and the average gross size was 3.7 x 2.6 x 1.6 mm (length, width, height). The average size of the thyroid lobules assessed sonographically was 2.3 x1.6 x 0.8 mm (length, width, height). Normal parathyroid glands can be identified using high-resolution ultrasonography. But some thyroid lobules will be misinterpreted as parathyroid glands; this will result in false positives when identifying parathyroid glands with ultrasonography.