Ultrasonographic adrenal gland measurements in clinically normal small breed dogs and comparison with pituitary-dependent hyperadrenocorticism.

Ultrasonography is a sensitive and specific screening method for assessing the adrenal glands. The upper limit of the normal adrenal gland width is used as 7.5 mm. It is not known if adrenal gland width remains consistent with body weight. A reliable criterion of adrenal gland width in small breed dogs should be established. Small breed dogs with body weights of less than 10 kg were divided into two groups: 189 normal dogs and 22 dogs with pituitary-dependent hyperadrenocorticism (PDH). A retrospective study was conducted on dogs seen between January 1, 2006, and February 10, 2008. One hundred eighty-nine dogs of 14 different small breeds were enrolled in the normal adrenal gland group; the median gland width was 4.20 mm. Twenty-two dogs were in the PDH group; the median gland width was 6.30 mm. The cut-off value between normal adrenal glands and PDH was 6.0 mm. This figure gave a sensitivity and specificity of 75 and 94%, respectively, for detecting PDH. The adrenal gland appeared as a peanut shape with homogeneous hypoechoic parenchyma in normal dogs and in most dogs with PDH as well. This study was performed in a large population of small breed dogs and suggests that the normal adrenal gland size in small breed dogs is smaller than previously reported. We believe that a cut-off of 6.0 mm may be used as the criterion for differentiating a normal adrenal gland from adrenal hyperplasia.