Giglio R, Berry C, Hernandez JA.
Introduction/Purpose: The value of diagnostic imaging in predicting canine adrenal malignancies has been proven. Previous investigations in dogs using ultrasonography (US) and computed tomography (CT) have found that evidence of adjacent vascular invasion, presence of adrenal mineralization, and enlargement of local lymph nodes are features suggestive of adrenal malignancy. The most common malignant adrenal neoplasms seen in dogs are pheochromocytoma (PHEO) and adenocarcinoma (ADC). The objective of this study was to evaluate the ability of CT findings to differentiate between ADC and PHEO.
Methods: The University of Florida Veterinary Hospital database was searched for dogs with histologically confirmed malignant adrenal neoplasms that had a contrast abdominal CT examination between January 2007 and March 2013. Twenty five dogs (14 PHEO and 11 ADC) met the inclusion criteria. CT characteristics were evaluated, including adrenal length, width, and height (mm), presence of mineralization (yes/no), evidence of vascular invasion (yes/no), and pre and post contrast HU measurement of the adrenal masses (average of three consecutive measurements, excluding areas of mineralization). Comparisons between dogs diagnosed with ADC and PHEO were conducted using the non-parametric Wilcoxon rank sum test or a chi-square test. A p value of < 0.05 was considered significant. Receiver operating characteristic curve analysis was used to assess the diagnostic performance of HU pre and HU post for diagnosis of ADC versus PHEO.
Results: ADC and PHEO were the only malignant adrenal neoplasms identified in our study sample. There were no statistical differences between ADC and PHEO for the features of adrenal length, width, and height (mm), evidence of vascular invasion, and parenchymal mineralization. HU pre values (mean ± sd) were higher in dogs with PHEO (44.5 ± 15.5 mm), compared to dogs with ADC (28.2 ±14.5) (p < 0.01). Similarly, HU post values were higher in dogs with PHEO (109.3 ± 28.7 mm), compared to dogs with ADC (70.3 ±27.2) (p < 0.01). Using a cut-off value of HU pre <: 37, the sensitivity and specificity of HU pre for diagnosis of PHEO vs ADC = 85% (95% CI = 57, 98%) and 72% (39, 94%), respectively. Using a cut-off value of HU post <: 89, the sensitivity and specificity of HU post for diagnosis of PHEO vs ADC = 78% (95% CI = 49, 95%) and 81 % (48, 97%), respectively.
Discussion/Conclusion: Suspected malignant adrenal masses with CT numbers higher than 37 HU pre contrast and 89 HU post contrast are more likely to be PHEO. However other adrenal malignancies, such as metastatic carcinoma, were not included in our study sample.