Metastasis or adenoma? Computed tomographic evaluation of the adrenal mass

Determining the nature of an adrenal mass is often a clinical challenge. To determine if unenhanced computed tomographic (CT) scanning can differentiate benign adenomas from metastases. Twenty-four pathologically proven adrenal masses were retrospectively correlated with their appearance on unenhanced CT scanning. Metastases were significantly larger than adenomas and had higher attenuation coefficients. A sensitivity-to-specificity ratio of 33:100 was achieved at a threshold of 0 Hounsfield units (HU), while a threshold of 10 HU produced a ratio of 58:92. A threshold size of 2.5 cm produced a ratio of 58:100. Attenuation and size were the only useful criteria for differentiating adenomas from metastases. Measuring the size and attenuation of adrenal masses can help identify benign adenomas. Lesions exceeding specific thresholds may still be benign and may require biopsy. We advocate documenting lesion stability for longer than is usually done, as one metastatic lesion remained without significant change in appearance for 18 months.