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 pheochromocytoma 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 cytopathologists. 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 distinguishing 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.