Ultrasound has increasingly become an effective tool for measuring adrenal glands in a small animal. The adrenal glands are essential components of the endocrine system and a wide variety of clinical symptoms may arise from their deranged function. With radiography, adrenal glands cannot be observed
(Kealy et al., 2012), unless they are highly swollen or mineralised. The advantages of ultrasonography include the ability to image both normal and abnormal glands, the ease and rapidity of the procedure, the lack of the need for anesthesia and the availability of ultrasound to practitioners. Nevertheless, the difficulty of imaging the adrenal glands should not be under-estimated. Even for a skilled sonographer, the small size of the glands; the deep and often unpredictable location of the glands are causes of difficulty in assessing adrenal glands. Ultrasonography can be used to evaluate different parameters, such as size, shape, margins, echogenicity and structure. The left adrenal gland is situated cranio-medial to the left kidney, ventro-lateral to aorta, between the origin of cranial mesenteric and left renal arteries. The right adrenal is situated cranio-medial to the hilus of right kidney, dorsal or dorso-lateral to caudal vena cava, cranial to right renal artery and cranial mesenteric artery. The phrenico-abdominal artery is dorsal to each adrenal gland, whereas the phrenico-abdominal vein is ventral. The adrenal glands are small, elongated, structures surrounded by fat. The left adrenal gland, having a “dumbbell” or “peanut” shape, is centrally constricted with enlarged extremities. The right adrenal gland is shaped like a “coma,” “wedge,” or “boomerang.” They are asymmetric in shape divided into cranial and caudal poles
(Tidwell et al., 1997; Anderson, 2011).
Place of study
The present study was carried out in the Department of Veterinary Surgery and radiology at the Teaching Veterinary Clinical Complex (TVCC), (Kothari veterinary hospital), College of Veterinary Science and Animal Husbandry, U. P. Pt Deen Dayal Upadhyaya Pashuchikitsa Vigyan Vishwavidyalaya Evam Go Anusandhan Sansthan, Mathura (UP).
Subjects of study
The present study was conducted on 18 apparently healthy dogs of different age groups. The dogs were allotted to three groups of six each.
Group I : Animals of 01 month to 09 months of age.
Group II : 09 months to 6 years of age.
Group III : Above six years of age.
The Esaote® MyLab30vetGold, Esaote Europe B.V., Philipsweg 1, 6227 AJ Maastricht, The Netherlands with 7.5 MHz LA523 transducer, was used to scan the adrenal glands per-cutaneously. The animals were subjected to ultrasonographic analysis without the use of any anaesthesia or sedatives in lateral recumbency. Area immediately behind the last rib shaved for the scanning of left and right adrenal glands, but the area was extended cranially up to the last intercostal space for right adrenal gland. The animals were restrained in the lateral recumbency to scan the adrenal glands. Adequate amount of coupling gel was applied over the transducer as well as the area of interest in order to ensure an intimate contact between skin and transducer head. Animals were left undisturbed throughout the examination procedure in order to get optimum results.
Method
The left adrenal gland was examined by placing the transducer in the subcostal region (immediately after the last rib) in the dorsal plane (along the length of the body parallel to the dog’s dorsum) and positioning the aorta and caudal vena cava in the long axis. The transducer was then cranially moved down to the left kidney level, holding the aorta in view and the left renal artery and vein was located. To find the left adrenal gland in the long axis, the transducer was rotated 45°C in clockwise direction and gently swept cranial to the renal artery and vein. When the adrenal gland was imaged, the aorta and kidney were not always visible in the same field of view, but other structures were visualized in some ultrasonograms, namely the adrenal gland along with the aorta and kidney in the same region. For locating of the right adrenal gland, the dog was placed in left lateral recumbency. The transducer was placed behind the last rib in the sub-lumbar area, in all the animal and intercostal approach was not needed to locate the right adrenal gland. The aorta and caudal vena cava were again located in the long axis in the dorsal plane. The transducer was then slid cranially, keeping the caudal vena cava in view. The adrenal gland was located along side and dorsal to the caudal vena cava. For measuring the length, the longitudinal sectional views of each adrenal were frozen when maximum length was visible. Similarly, for width measurement the image was frozen when maximum width of either of the poles was visible. The length, cranial pole diameter and the caudal pole diameter were measured on these frozen images of adrenal glands using the in-built callipers (Fig 1).
The different measurements
i.e. length, cranial pole diameter, caudal pole diameter of both the adrenal glands were measured using the in-built ultrasonographic machine callipers (Table 1).
Ultrasonographic measurements of left adrenal gland
The length of the left adrenal gland in this study was 1.61±0.17 cm in Group I, 2.2±0.177 cm in Group II and 2.44±0.30 cm in Group III.
Lobetti et al., (2016) recorded median left adrenal lengths of 1.77 cm, 2.08 cm and 2.1 cm in 3 different groups of dogs. In a study performed by
Hoerauf and Reusch (1999), the standard range of left adrenal gland length was 1.32 cm to 2.63 cm in 20 dogs, while the range for left adrenal gland length was 1.07 cm to 5.02 cm, as stated by
Douglass et al., (1997). The cranial pole diameter of left adrenal gland was 0.32±0.033 cm, 0.49±0.048 cm and 0.54±0.08 cm in Group I, II, III, respectively in the present study. In a study done by
Shaghayegh et al., (2011), the mean cranial pole diameter was reported to be 0.42±0.06 cm. In the present study, the caudal pole diameter (thickness) of left adrenal was 0.35± 0.037 cm, 0.54±0.029 cm and 0.52±0.08 cm in Groups I, II, III, respectively. In a study by
Douglass et al., (1997), the range of caudal pole width was 0.19 cm to 0.124 cm, while
Hoerauf and Reusch (1999) recorded a normal range of the thickness of the left adrenal gland from 0.30 cm to 0.52 cm.
Grooters et al., (1996) reported a median thickness of the left adrenal gland in control dogs to be 0.6 cm, while
Choi et al., (2011) found a mean value of 0.432±1.00 cm for the left adrenal gland.
Lobetti et al., (2016) recorded that the median left adrenal gland thickness was 0.31 cm, 0.4 cm and 0.6 cm in three groups of their study.
Ultrasonographic measurements of right adrenal gland
The length of right adrenal gland was 1.57±0.12 cm in Group I, 2.1±0.10 cm in Group II and 2.20±0.27 cm in Groups III.
Lobetti et al., (2016) recorded the median length of right adrenal gland in three groups of dogs. It was 1.75 cm group I, 1.8 cm group II and 2.03 cm in group III. The typical range of the right adrenal gland length was 1.24 cm to 2.26 cm in 20 dogs as reported by
Hoerauf and Reusch (1999), while the right adrenal gland length ranged from 1.00 cm to 3.93 cm as reported in a study by
Douglass et al., (1997). In the present study, the cranial pole diameter of right adrenal gland was 0.36±0.03 cm, 0.48±0.03 cm and 0.61±0.07 cm in Groups I, II and III, respectively. The mean diameter of the cranial pole was reported as being 0.46±0.06 cm, in a research carried out by
Shaghayegh et al., (2011). In the present study, the caudal pole diameter of right adrenal gland was 0.39±0.04 cm, 0.54±0.05 cm and 0.56±0.08 cm in Groups I, II and III, respectively. In a study by
Douglass et al., (1997), the range of caudal pole width was 0.31 cm to 0.120 cm, while
Hoerauf and Reusch (1999) recorded the normal range of right adrenal gland thickness from 0.31 cm to 0.60 cm, respectively.
Grooters et al., (1996) indicated the thickness of the median right adrenal gland in control dogs was 0.6 cm. Similarly,
Choi et al., (2011) found the mean value of right adrenal gland thickness to be 0.421±1.00 cm.
Lobetti et al., (2016) reported that the median right adrenal gland thickness was 0.34 cm, 0.37 cm and 0.6 cm in three groups studied by them.
De chalus et al., (2013) defined a new upper threshold of 0.95 cm for the Labrador Retrievers and 0.67 cm for the Yorkshire Terriers for the right adrenal gland height at the caudal pole measured in a longitudinal plane.
Anaesthesia is not needed for ultrasonography of adrenal glands in dogs. Subcostal approach is the best way to scan left and right adrenals. Adrenal gland scanning can be achieved easily by using a 7.5 MHz Linear transducer in lateral recumbency by placing the probe caudal to the last rib and ventral to the lumbar process. Because of their size and location, it takes a great degree of patience to scan adrenal glands. Despite of its cranial position it is hard to locate right adrenal gland. Dimensions of the adrenal glands taken in this study can be used as reference values and aid in the diagnosis of adrenal pathologies. The diameter of the caudal pole is a valid metric to determine the adrenal gland thickness. Hyperadrenocorticism, hypoadrenocorticism and adrenal tumors can be diagnosed by measuring the thickness of the caudal poles.
