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tvpjournal.com | January/February 2016 | Today's VeTerinary PracTice canine PiTuiTary dePendenT HyPeradrenocorTicism series Peer reviewed 41 combination of these. Metastasis can be confrmed by ultrasound-guided biopsy, but differentiating benign from malignant AT often is diffcult, even with histopathologic examination. Pituitary Imaging Pituitary imaging provides valuable information regarding treatment options and prognosis. 37 Pituitary lesions range from microscopic nests of hyperplastic cells to large tumors. Absence of neurologic abnormalities does not exclude pituitary macrotumors (ie, tumors that are > 1 cm in diameter, extend above the sella turcica, or have a pituitary:brain ratio of > 0.31). Indications. Pituitary imaging should be considered for all dogs at time of PDH diagnosis, especially if hypophysectomy or radiation therapy is being considered. If clinical features suggest a pituitary macrotumor, confrmation requires imaging; clinical signs include: • Disorientation and aimless wandering • Severe polyuria/polydipsia • Lethargy • Hyporexia to anorexia • Visual impairment • Seizures (in some patients). Test Results. Because pituitary lesions may be quite small, contrast-enhanced CT and MRI (Figure 4 and Figures 5–6, page 42) may identify normal sized pituitary glands in dogs with PDH. However, dynamic contrast-enhanced CT takes advantage of the pituitary gland's blood supply: • The posterior pituitary gland's blood supply is direct (arterial) • The anterior pituitary gland's blood supply is mainly indirect via the pituitary portal system. In dogs with normal pituitary glands, after IV administration of contrast medium, the posterior pituitary gland can be identifed frst—this phase is called the "pituitary fush." Its absence indicates atrophy of the posterior pituitary gland due to compression by a pituitary tumor. Displacement or distortion of the fush can be used to identify and localize anterior pituitary microtumors. Dorsal displacement and decreased signal intensity of the posterior lobe on T1-weighted MRI indicates the presence of a microtumor. 38,39 IN SUMMARy Diagnosis of PDH requires incorporating information from the history, physical examination, and routine laboratory tests. Specifc endocrine tests FIGURE 3. Ultrasound (A) and surgical view (B) of adrenal adenoma. A B FIGURE 4. Axial (A) and sagittal (B) T1 post contrast MRI images from a dog with PDH and large pituitary macroadenoma. B A