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Today's VeTerinary PracTice | January/February 2016 | tvpjournal.com canine PiTuiTary dePendenT HyPeradrenocorTicism series Peer reviewed 40 Dexamethasone Suppression with UCCR Decreased blood cortisol concentration after dexamethasone administration is refected in decreased UCCR. After the patient's owner/handler collects a morning urine sample on 2 consecutive days, 3 doses of dexamethasone (0.1 mg/kg PO) are administered at 6 to 8 hour intervals, with a third urine sample collected the next morning. Decrease in the third UCCR to < 50% of the mean cortisol basal values is consistent with PDH. Lack of suppression does not confrm AT. In 160 dogs with HAC (49 with ATs, 111 with PDH), the UCCR in 72% of dogs with PDH suppressed to < 50% of the basal UCCR, while the other 28% of those with PDH were dexamethasone- resistant. In dogs with ATs, maximum suppression was 44% of the baseline sample. 31 DIFFERENTIATING PDH FROM ADH: IMAGING While imaging can be very helpful in differentiating PDH from ADH, it cannot be used to establish a diagnosis of HAC. Moreover, fnding normal adrenal glands on imaging studies does not rule out HAC. Radiography Imaging results may include: • Abdominal distension • Good contrast due to abdominal fat deposition • Hepatomegaly • Bladder distension • Mineralization of bronchi and pulmonary interstitium, and of dermal and subcutaneous tissues in areas predisposed to calcinosis cutis. A small liver makes HAC unlikely. An AT may be visualized either due to mass effect or tumor calcifcation. 32,33 Adrenal Gland Imaging Adrenal gland width is the most informative parameter identifed on ultrasonography (Figure 1 ). However, the following may affect correct measurement: • Long axis of adrenal gland often is misaligned with either the medial or dorsal plane of the body • Cross-sectional images may lead to oblique views and miscalculation of glandular dimensions • Breed and body size differences • Macronodular hyperplasia (a rare form of PDH) and some ATs can be difficult to differentiate. Test Results. In dogs with PDH, ultrasonography reveals normal sized or enlarged adrenal glands that are typically symmetrical; however, mild asymmetry may occur. In dogs with ATs, ultrasonography reveals moderate asymmetry, contralateral adrenocortical atrophy (adrenal width < 4–5 mm), destruction of normal tissue architecture, or some combination of these fndings. 34,35 Ultrasonography can also estimate AT size and possibly vascular or local soft tissue invasion. Although most ATs are unilateral, bilateral tumors may occur and in these patients, endogenous ACTH concentrations should be determined. Metastasis. When an AT has been confrmed, certain thoracic and ultrasonographic fndings suggest malignancy, including: • Adrenal gland width > 4 cm • Invasion into the vena cava or adjacent tissues. However, computed tomography (CT) (Figure 2) and magnetic resonance imaging (MRI) are more sensitive techniques to identify vascular invasion and detect metastases. 36 Adrenalectomy should not be performed without confrming the presence of an AT (and atrophy of contralateral adrenal gland) by abdominal ultrasonography (Figure 3), CT, MRI, or some FIGURE 1. Ultrasound image of adrenal adenoma. FIGURE 2. CT image of large right adrenal adenoma between the right kidney and caudal vena cava.