Accuracy of cytology in distinguishing adrenocortical tumors from pheochromocytoma in companion animals.

Background: The distinction between adrenocortical tumors and pheochromocytoma can be challenging using clinical findings, diagnostic imaging and laboratory tests. Cytology might be a simple, minimally invasive method to reach a correct diagnosis. Objectives: The purpose of this study was to assess the accuracy of cytology in differentiating cortical from medullary tumors of the adrenal glands in dogs and cats. Methods: Cytologic key features of adrenocortical tumors and pheochro- mocytoma were defined by one reference author. Cytologic specimens from primary adrenal tumors were submitted to 4 cytopathologists who were asked to classify the tumors based on the previously defined key features without knowledge of previous classification. Results: Twenty specimens from histologically confirmed adrenal tumors (Group 1) and 4 specimens from adrenal tumors causing adrenal- dependent Cushing’s syndrome (Group 2) were evaluated by the 4 cyt- opathologists. Accuracy in differentiating cortical from medullary origin ranged from 90% to 100%, with a Kappa coefficient of agreement between cytopathologists of 0.95. Conclusions: The origin of an adrenal tumor can be easily determined by cytology alone in many cases. However, cytology was not reliable in distin- guishing benign from malignant neoplasia. Additional studies are needed to assess possible risks and complications associated with fine-needle biopsy of adrenal tumors in dogs and cats.