Accuracy of focal cystic appearance within adrenal nodules on contrast-enhanced CT to distinguish pheochromocytoma and malignant adrenal tumors from adenomas

Purpose To determine the accuracy of cystic appearance within adrenal masses on contrast-enhanced CT in distinguishing pheochromocytomas and malignant adrenal tumors from adenomas. Methods We performed a retrospective review of adult patients with pathologically proven adrenal tumors who underwent contrast-enhanced abdominal CT. There were 92 patients (mean age 64.7 years, 52 men) with 22 pheochromocytomas, 34 malignant masses, and 36 adenomas. Two abdominal radiologists independently reviewed CT images to determine the presence of cystic appearance within the adrenal masses, defined as focal regions of low attenuation within the tumor that subjectively had fluid density. Results Cystic appearance was present in 12/22 (55%, 95% CI 32-76%) pheochromocytomas (mean size 5.3 cm), 15/34 (44%, 95% CI 27-62%) malignant masses (mean size 5.8 cm), and 2/36 (5.6%, 95% CI 0.7-9%) adenomas (mean size 3.2 cm). Sensitivity and specificity of cystic appearance for distinguishing pheochromocytoma or malignant masses from adenomas were 48.2% (95% CI 34.7-62.0%) and 94.4% (95% CI 81.3-99.3%), respectively. Cystic appearance was a significant predictor of tumor type (p = 0.015) even after controlling for tumor size. Reader agreement for cystic appearance was almost perfect with a kappa of 0.85. Conclusion Cystic appearance in adrenal tumors on contrast-enhanced CT has high specificity and low sensitivity for distinguishing pheochromocytoma and malignant adrenal masses from adenomas.