Differentiation of lipid-poor adrenal adenomas from non-adenomas with magnetic resonance imaging: Utility of dynamic, contrast enhancement and single-shot T2-weighted sequences

Purpose To evaluate the utility of dynamic, contrast-enhanced magnetic resonance imaging (MRI) in combination with single-shot T2-weighted (ssT2) sequences in the differentiation of lipid-poor adrenal adenomas from non-adenomas. Materials and methods This retrospective study was approved by the institutional review board and is HIPAA compliant. Between January 2007 and December 2010, 46 patients with MRI demonstrating a lipid-poor adrenal lesion who underwent either surgical resection or a minimum of 24 months of imaging follow-up were identified retrospectively. All images were retrospectively reviewed in blinded fashion by two radiologists. Each adrenal lesion was categorized by dynamic enhancement features and qualitative signal on ssT2 images and was categorized as an adenoma if it demonstrated homogenous enhancement in the arterial phase, washout with capsule enhancement in the delayed phase, and T2 signal isointense to normal adrenal tissue. Any lesion that did not fulfill all the criteria was classified as a non-adenoma. Sensitivity, specificity, positive predictive value, negative predictive value, and accuracy for characterization of adenoma were calculated for each reader with 95% confidence intervals. A κ test assessed level of agreement between readers. Results Application of our criteria lead to an MRI diagnosis of lipid-poor adrenal adenoma with a sensitivity of 84.2-89.5% (16/19-17/19), specificity of 96.3% (26/27), positive predictive value of 94.1-94.4% (16/17-17/18), negative predictive value of 89.7-92.9% (26/29-26/28), and accuracy of 91.3-93.5% (42/46-43/46). Agreement between the two readers showed substantial κ agreement for the differentiation of adenoma from non-adenoma. Conclusions Dynamic, contrast-enhanced T1-weighted three-dimensional gradient echo sequences in combination with ssT2 images can accurately differentiate lipid-poor adrenal adenomas from non-adenomas.