Maximum adrenal thickness appears to be a better indicator of enlargement than length, which can be difficult to assess due to the organ’s shape. Thickness measurement also appears to be more reproducible when assessed by different sonographers. The ACVIM and ECVDI consensus recommends measuring thickness at the caudal poles of the adrenal glands; however, the values presented in publications usually refer to the maximum thickness of the adrenal gland regardless of its pole. This fact should be taken into account when using reference data. An index relating adrenal gland thickness to aortic width has also been developed for dogs.
Maximum thickness
Adrenal gland thickness is usually assessed in the sagittal plane of the adrenal gland as visualized through the abdominal wall. In some dogs, imaging through the intercostal window may be helpful in assessing the right adrenal gland. Adrenal gland thickness corresponds to the segment perpendicular to its longitudinal axis.
N In the reference ranges below, the values listed correspond to 95% reference intervals—it can be assumed that the thickness of 95% of healthy adrenal glands falls within the indicated values. The values in square brackets represent 90% confidence intervals—there is a 90% probability that a given value falls within the interval indicated in brackets.
DOG
| body weight [kg] | lower limit of the normal range for the left adrenal gland [mm] | upper limit of the normal range for the left adrenal gland [mm] | lower limit of the normal range for the right adrenal gland [mm] | upper limit of the normal range for the right adrenal gland [mm] |
| >2,5 – 5 | 3.2 [2.9 – 3.5] | 5.1 [4.9 – 5.3] | 2.8 [2.4 – 3.2] | 5.3 [5.0 – 5.7] |
| >5 – 10 | 3.0 [2.7 – 3.4] | 5.5 [5.1 – 6.0] | 3.4 [2.8 – 3.8] | 6.8 [6.2 – 7.1] |
| >10 – 20 | 3.8 [3.3 – 4.1] | 6.4 [6.0 – 6.8] | 3.5 [2.9 – 4.0] | 7.5 [6.9 – 8.2] |
| >20 – 40 | 4.7 [4.3 – 5.1] | 7.3 [6.9 – 7.7] | 5.1 [4.4 – 5.5] | 8.7 [8.2 – 9.3] |
C Using the above cut-off values, ultrasound was a sensitive (95.6%) method for detecting hyperadrenocorticism. The specificity of the method was not estimated.
C The lower limit for the thickness of the left adrenal gland is consistent with the findings of an earlier publication (Wenger et al., 2010), which demonstrated that its maximum thickness of <2.8 mm is a highly sensitive (90%) and specific (100%) indicator of hypoadrenocorticism. The authors of that publication note, however, that thickness of <3.2 mm is already indicative of hypoadrenocorticism.
CAT
| body weight [kg] | lower limit of the normal range [mm] | upper limit of the normal range [mm] |
| < or equal to 4 | 2.4 [2.2 – 2.6] | 3.9 [3.7 – 4.1] |
| 4 – 8 | 2.6 [2.4 – 2.8] | 4.8 [4.6 – 5.1] |
Index: Maximum thickness of the caudal pole: Aorta
DOG
The maximum thickness of the caudal pole of the adrenal gland is divided by the maximum width of the abdominal aorta lumen (the measurement segment does not include the vessel walls). The aorta is measured on its longitudinal cross-section, just before the origin of the left renal artery.
| body weight [kg] | left adrenal gland | right adrenal gland |
| <10 | 0.78 ± 0.16 (0.62 – 0.94) <0.47 – 1.44> | 0,84 ± 0,23 (0,61 – 1,07) <0,36 – 1,89> |
| 10-20 | 0.64 ± 0.15 (0.49 – 0.79) <0.4 – 1.25> | 0,72 ± 0,18 (0,54 – 0,9) <0,4 – 1,16> |
| >20 kg | 0.58 ±0.12 (0.46 – 0.7) <0.23 – 0.83> | 0.65 ± 0.16 (0.49 – 0.81) <0.37 – 0.99> |