The incidentally discovered adrenal mass

Jennfier DeBerry, DVM, DACVIM
Veterinary Specialty Hospital, San Diego
Posted on 2016-12-13
 

With improved imaging techniques, the number of adrenal masses detected in animals with problems unrelated to adrenal function is common. Abdominal ultrasound is part of the “minimum data base” in the non-invasive diagnostic workup of the sick or elderly pet. The patient may have non-specific signs of illness, or may simply be perceived by the owner of “getting old”.

Primary adrenal tumors can be functional or non-functional; they may be malignant or benign in nature. Tumors can arise from all layers of the adrenal cortex, or the adrenal medulla. Adrenal tumors may secrete cortisol, aldosterone, sex hormones, catecholamines, or steroid precursors.

Diagnostic Approach

When an adrenal mass is found during screening of a geriatric patient, there are several ways to proceed. Adrenal masses are presumed malignant: they won’t go away or get smaller (unless the “mass” was actually an artifact). Surgery is recommended for tumors > 3cm in width, and for all functional or invasive tumors.

The likelihood of the mass causing the pet’s clinical signs should be considered so other problems aren’t ignored. For example, an adrenal mass is unlikely to cause vomiting, severe weight loss, anorexia or profound lethargy, and a cause for such signs should be pursued. However, many non-specific signs (such as generalized malaise or weakness), or clinical signs of a functional tumor (signs of Cushing’s syndrome, hypertension) could be attributed to an adrenal tumor.

The diagnostic approach of an adrenal tumor includes reviewing the history, physical exam, and preliminary laboratory findings.

Abnormalities consistent with hyperadrenocorticism (HAC) should alert the clinician to rule out adrenal dependent HAC due to a cortisol-secreting tumor, or the tumor may be secreting a sex hormone or a steroid precursor.

Blood pressure should be measured, as all functional adrenal tumors can potentially cause hypertension. If the blood pressure is initially normal, repeat measurement is warranted because hypertension may be intermittent. The appearance of the opposite gland is important to assess. A small contralateral gland suggests cortisol secretion by the tumor, but the contralateral gland may also appear normal even in cortisol-secreting tumors. Endocrine testing should answer this question: “Is this adrenal tumor secreting cortisol?” This is answered best with the high dose dexamethasone suppression test (HDDST), the most specific adrenal function test to rule out adrenal dependent HAC. If suppression occurs, it is unlikely that the adrenal tumor is secreting cortisol. A low dose dexamethasone suppression test (LDDST) can be used. However, 40% of dogs with pituitary-dependent HAC will not suppress, thus if suppression is not demonstrated with the LDDST, the HDDST is still recommended (especially if there are other suggestive signs of HAC, and/or the contralateral gland is small). ACTH stimulation test is insensitive for adrenal dependent Cushing’s syndrome; upwards of 50% of cortisol-secreting tumors will test negative. If suppression occurs, further testing for occult (formerly known as atypical) Cushing’s (a complete adrenal panel consisting of pre and post-ACTH cortisol, aldosterone, estradiol, progesterone, androstenedione, testosterone, and 17-OH progesterone) to the University of Tennessee, UC Davis, or Cornell University can be considered.

Urinary normetanephrine and inhibin levels may be useful in the biochemical diagnosis of pheochromocytoma. A urinary normetanephrine:creatinine ratio 4 times normal (control sample), is highly suggestive of pheochromocytoma.¹ Submit acidified urine along with urine from a control sample to Marshfield labs.

In neutered dogs, adrenocortical tumors (and PDH) but not pheochromocytomas were associated with increased serum inhibin concentration; undetectable inhibin levels was supportive of a pheochromocytoma in neutered dogs with adrenal tumors.

Sensitivity and specificity of serum inhibin concentration for identifying an adrenal tumor as a pheochromcytoma were 100 and 88.9%, respectively. Fasted serum can be submitted to UC Davis.²

If a pheochromocytoma is suspected or confirmed, preoperative treatment with an alpha-adrenergic blocker (phenoxybenzamine or prazosin), especially if the patient is hypertensive, may decrease potential perioperative complications.

Alternatively, the incidentally discovered adrenal mass can be ignored. If the presence of a mass is questionable, re-evaluation in a month is reasonable. In older or debilitated patients, or with concurrent illness making them less desirable surgical candidates, or if the owner is reluctant to pursue surgery, monitoring the adrenal tumor is reasonable. Ultrasound can be rechecked in one to three months. If there is substantial growth, surgery should be reconsidered. Three-view thoracic radiographs (or thoracic CT) are recommended prior to adrenalectomy. Pre-operative abdominal CT scan may provide additional information for surgical planning. If surgery is not an option, medical therapy for adrenal dependent Cushing’s syndrome can be successful at minimizing clinical signs. Both mitotane and trilostane can be used.
 

References

1. Quante S, et al. Urinary catecholamine and metanephrine to creatinine ratios in dogs with hyperadrenocorticism or pheochromocytoma, and in healthy dogs. J Vet Intern Med 2010;23:1093-7.
2. Brömel C, et al. Serum inhibin concentration in dogs with adrenal gland disease and in healthy dogs. J Vet Intern Med 2013;27:76-82.