Transrectal ultrasonography of the left adrenal gland in healthy horses.

Little information is available on medical imaging of the adrenal glands in horses. We investigated the feasibility of transrectal ultrasonography to characterize the normal equine adrenal gland. Transrectal ultrasonography was performed in 25 healthy horses using a 7.5 MHz linear array probe at a displayed depth of 8 cm. Transrectal ultrasonography of the right adrenal gland was not feasible. For the left adrenal gland, the left kidney, the abdominal aorta, the left renal artery, the left renal vein, and the cranial mesenteric artery were used as landmarks. The size of the left adrenal gland was variable, but it generally appeared as a long, flat structure with a hyperechoic medulla surrounded by a hypoechoic cortex. The most cranial part of the gland could not be delineated appropriately in 11 horses (44%). The mean (+/-SD) thickness of the gland and medulla was 0.66 +/- 0.15cm (n = 25) and 0.28 +/- 0.09 cm (n = 25) near the caudal pole, 0.87 +/- 0.25 cm (n = 14) and 0.40 +/- 0.18 cm (n = 12) near the cranial pole, and 0.89 +/- 0.18 cm (n = 25) and 0.36 +/- 0.13 cm (n = 25) in the middle of the gland, respectively. The mean (+/-SD) length of the entire adrenal gland and of the medulla was 6.22 +/- 0.77 cm (n = 14) and 5.45 +/- 0.71 cm (n = 6), respectively. Transrectal ultrasonography allowed adequate visualization of the left adrenal gland in horses.