142 Figure 142.1 shows a contrast-enhanced soft tissue window, transverse CT slice through the mid-abdomen of an elderly male neutered Labrador retriever presenting with owner complaints of sporadic, paroxysmal diarrhea and vomiting, polydispsia/polyuria, weakness, occasional collapse, and bouts of anxious behavior with tachypnea. The structure indicated by the asterisk and arrow is approximately 1.5 cm in the longest dimension. On physical examination, the dog was weak, unwilling to rise, and persistently tachypneic. Routine clinical chemistry examination was unremarkable other than elevated total and ionized calcium concentrations. Figure 142.1 https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429401725/f4da9fa5-f3c9-42b7-a3b4-01cbbbe79e20/content/fig142_1_C.jpg"/>

i. What is the highlighted structure?

ii. What are the expected clinical and biochemical changes seen with common tumors of this organ? Can you account for all of this dog’s historical problems and clinical findings with this imaging finding?

iii. The results from ACTH stimulation and low-dose dexamethasone suppression testing are all within normal limits, making the diagnosis of adrenal-dependant hyperadrenocorticism highly unlikely. You suspect that the dog has a pheochromocytoma. How could you obtain evidence to support or rule out this suspicion?

iv. What is the tissue of origin of pheochromocytomas?

v. Serial determination of systolic blood pressure in this patient reveals persistent hypertension, accompanied by paroxysmal bouts of tachycardia. How would you plan to treat this patient?

vi. Even given the presumed diagnosis of pheochromocytoma, can you account for all of this dog’s historical problems and clinical findings?238