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Case Study: Ferret Adrenal Gland Disease

By Linda E. Luther, DVM, DACVIM (Internal Medicine)
(5/16/05)

Indications

Anorexia
Alopecia
Pruritus
Vulvar enlargement in females
Dysuria/urinary obstruction in males
Aggression

Adrenal gland disease is commonly recognized in pet ferrets in the United States, and differs from the syndrome of Cushing’s disease in dogs. Adrenocortical hyperplasia, or a functional adenoma or adenocarcinoma is typically present, but cortisol levels are usually normal, and elevations of the sex hormones such as estradiol, 17-hydroxyprogesterone and androstenodione are seen instead. The clinical signs commonly seen include alopecia with or without pruritus, vulvar enlargement in females and dysuria or urinary blockage in males occurring due to enlarged or cystic prostatic tissue. Aggression and PUPD have also been reported. The underlying pathogenesis of the adrenal gland changes has been speculated to be related to early neutering, diet, indoor housing resulting in a lack of a photoperiod and inbreeding.

Diagnosis of adrenal disease in ferrets can be made by combining the clinical history with abdominal ultrasound and serum hormone assays. Results of a complete blood count and blood chemistry profile are usually normal, although anemia can be seen. Abdominal radiographs are usually nondiagnostic.

Ultrasound is a noninvasive, informative imaging method for the adrenal glands, and it provides detailed information about adrenal gland size and shape. Adrenal ultrasound in the ferret is typically performed using a ventral transabdominal approach, with the ferret in dorsal recumbancy and the ventral abdomen shaved. A 7.5 to 10 MHz transducer is most often employed. A complete abdominal ultrasound is performed in most cases in order to evaluate the other organs for lesions and to rule out lymphadenopathy, and as well to rule out that a female is still intact or has an ovarian remnant, or that a male does not have prostatic enlargement or cystic change. An ultrasound exam is often tolerated well, and can at times be done without sedation. However in an active patient, sedation can greatly enhance the ability to image the adrenals well.

Normal ferret adrenal glands are flat and bilobed in shape in the sagittal plane, and are usually homogeneous and hypoechoic to the surrounding fat. Corticomedullary distinction can be seen in some cases. Normal ferret adrenal size has been reported to be (length x thickness) 5.4-9.8 x 2.3-3.6 mm for the left adrenal gland and 5.8-10.5 x 2.2-3.8 mm for the right adrenal gland. The left adrenal gland is located medial and cranial to the cranial pole of the left kidney, ventrolateral to the aorta, between the cranial mesenteric and left renal arteries. The right adrenal gland is located between the medial aspect of the cranial pole of the right kidney and the caudal vena cava, cranial to the renal artery and vein. The phrenicoabdominal artery is located on the dorsal aspect of the gland, and the phrenicoabdominal vein on the ventral aspect. The long axis of the adrenal glands may not be parallel to the kidneys and great vessels, thus the landmarks may not be concurrently seen when the optimal plane for the adrenal glands is achieved.

The ultrasonographic change most commonly seen in ferret adrenal gland disease is an increase in pole thickness with a normal gland length. Increased thickness and length can both be seen in some cases, or the pole thickness may be normal but asymmetrical. The presence of an adrenal gland mass or nodule in a ferret is assumed to represent cortical neoplasia or hyperplasia, but the pattern of gland size and shape change has not been found to be specific to lesion type. Normal adrenal size and shape have been reported with adrenal hyperplasia and adenomas. When an abnormal adrenal gland is seen, it can be described as an adrenal mass if there is a diffuse increase in thickness and/or length, or as an adrenal nodule if there is a focal increase in thickness or an asymmetry of the poles. Bilateral adrenal involvement has been reported in approximately 20% of those ferrets with adrenal disease, although initial ultrasound examination did not always reveal that bilateral disease existed. Vascular invasion has not been reported to be identified ultrasonographically, but an absence of periglandular fat, direct contact with the aorta, caudal vena cava or liver, or deviation or compression of a vessel may be indirect evidence of vascular invasion and/or incomplete resectability. The parenchyma of an abnormal adrenal gland may become heterogeneous. Mineralization has only been reported in one adrenal adenocarcinoma, thus conclusions regarding the significance of this change cannot be made. Pheochromocytomas, originating from the adrenal medulla rather than the cortex, are rare in this species.

Further confirmation of adrenal disease in the ferret can be accomplished with hormone panels that measure serum estradiol, 17-hydroxyprogesterone and androstenodione. (www.vet.utk.edu/diagnostic/endocrinology). In a normal, neutered ferret, levels of these steroid hormones are very low. Intact ferrets have variable levels of these hormones present. In ferrets with adrenal disease, levels of one or more of these hormones may be high.

Therapy of hyperadrenocorticism in ferrets can be surgical or medical. Surgery involves adrenalectomy of the abnormal gland, which is straightforward for the left gland, but difficult for the right gland because of its proximity to the caudal vena cava. Rather than complete removal, a subtotal adrenalectomy is commonly done on the right. If all diseased tissue is removed, surgery may be curative. If the previous or new clinical signs appear after adrenalectomy surgery, a recheck ultrasound exam may help to rule out regrowth of an incompletely resected lesion. Medical therapy with mitotane, androgen receptor blockers, aromatase inhibitors and gonadotropin-releasing hormone analogs has been described. Medical therapy is not curative however, and may be unsuccessful in moderating clinical signs. When urinary blockage is present in a male ferret, urethral catheterization is indicated.

Figure 1

Figure 2

Figures 1 and 2. Sagittal views of the left adrenal gland from a neutered-male ferret with a history of recent aggressive behavior, and an elevated estradiol level, high normal 17-hydroxyprogesterone level and elevated androstenodione level. The adrenal gland is normal in shape and in the high normal size range (length: 0.83 cm; cranial pole width: 0.33 cm; caudal pole width: 0.32 cm).

Figure 3

Figure 4

Figures 3 and 4. Sagittal views of the right adrenal gland from the same ferret from figures 1 and 2 demonstrating normal shape, a thickened cranial pole width, and asymmetrical cranial and caudal pole widths (length: 1.05 cm; cranial pole width: 0.43 cm; caudal pole width: 0.28 cm). A layer of hyperechoic periglandular fat is seen surrounding the adrenal gland, suggesting that vascular invasion of the caudal vena cava has not occurred.