Abstract
Background:
Computed tomography (CT) is useful for evaluating the anatomical position of the adrenal gland and the presence of adrenal tumor (AT) metastasis or vascular invasion from ATs.
Aim:
To determine a weight-independent reference for adrenal gland size in normal dogs using CT.
Methods:
The medical records database of Gifu University was searched for data collected from April 2010 to December 2015 for records of dogs that underwent abdominal CT. The CT images were retrospectively analyzed using a Digital Imaging and Communications in Medicine viewer. The ratios of the minor axes of the adrenal glands to the height of the spinal cavity were investigated.
Results:
In total, 939 dogs were included. The left and right adrenal minor axes showed a moderate positive correlation with body weight (right: r = 0.61, p < 0.05; left: r = 0.54, p < 0.05). The L4 spinal cavity height showed a strong positive correlation with body weight (r = 0.82, p < 0.05). The left and right adrenal minor axis/L4 spinal cavity ratio did not correlate with body weight (right: r = 0.02, p = 0.53; left: r = −0.082, p < 0.05). The 95% confidence intervals of the adrenal minor axis/L4 spinal cavity ratios were as follows: right: 0.5–1.3 and left: 0.5–1.4.
Conclusion:
These results indicate that the adrenal minor axis/L4 spinal cavity ratio can be used as an index of adrenal gland size that is not affected by body weight. Patients in whom the adrenal minor axis/L4 spinal cavity ratio exceeds the upper limit (right 1.3, left 1.4) may have adrenal swelling.

Key words: Adrenal size, Body weight, Canine, Computed tomography, Novel index