Reliability of CT attenuation value for adrenal masses

CT attenuation value is useful in the differential diagnosis of adrenal masses, and values <10 Hounsfield units (HU) can exclude malignancy and pheochromocytoma. However, few reports have examined the reliability of CT attenuation measurements. We examined the reliability of CT attenuation measurements made by surgeons not specialized in image reading.

A retrospective analysis of 313 patients (325 lesions) who underwent surgery at a single institution was performed.

One general surgeon and one endocrine surgeon independently measured CT attenuation values. The intraclass correlation coefficient and Cohen's kappa coefficient were used to analyze interobserver reliability. All cases were subjected for endocrine function tests and histopathologically diagnosed. Additional analyses included segmented regression for size-related measurement variability and multivariable analyses comparing aldosterone-producing adenomas (APAs) and cortisol-producing adenomas (CPAs).

The intraclass correlation coefficient between observers was 0.938 (95% CI: 0.923-0.949), and Cohen's kappa coefficient was 0.851 (95% CI: 0.781-0.922). Both observers measured all malignant adrenal tumors (such as adrenocortical carcinoma, metastatic adrenal carcinoma, and malignant lymphoma) and pheochromocytomas as ≥ 10 HU. CT attenuation values were significantly higher in CPAs than in APAs, independent of mass size (P < 0.001 for both observers).

CT attenuation value was shown to be reliable enough for simple measurements that could be performed by non-radiologists and was useful for excluding malignancy and pheochromocytoma.

This study reinforced evidence for the reliability of CT attenuation value. Even with a simple method that can be performed by non-radiologists, CT attenuation values were highly reliable and useful for excluding malignancy and pheochromocytoma. In addition, all lesions in this study were evaluated both endocrinologically and pathologically, giving high validity to the reference standard. These findings complement and further substantiate the latest clinical practice guidelines of the European Society of Endocrinology.