Distinguishing adrenal adenomas from non-adenomas with multidetector CT: evaluation of percentage washout values at a short time delay triphasic enhanced CT

Abstract

Many of the adrenal masses are discovered incidentally due to the increasing use of multidetector CT for different clinical problems, even in patients without endocrinological symptoms. Radiological studies reported the frequency of incidentalomas varies from 3 to 10% according to the age. 1,2 Although most of these lesions are non-functioning benign adrenal adenomas, other lesions also exist including hormone-producing adenomas, pheochromocytomas, adrenal carcinomas or metastases. 3,4 Hence, the differential diagnosis of adrenal lesions is still crucial. The detection of adrenal masses is troubling, particularly for patients with a history of malignant tumor. Assessment of adrenal masses requires an accurate diagnosis to determine appropriate therapeutic approach for the patient. Dedicated adrenal CT can provide several quantitative CT parameters that contribute to the diagnosis of adrenal lesions, such as lesion size, unenhanced attenuation, level of enhancement at early phase and delayed phase, wash-in attenuation at early phase, percentage washout ratio at delayed phase, and histogram analysis. Various threshold values and the corresponding diagnostic efficiency of these parameters that assist in differentiating between adrenal adenomas and non-adenomas at unenhanced and delayed enhanced CT have been reported. 5-10 The purpose of this study is to evaluate the diagnostic values of absolute percentage washout ratio (APW) and relative percentage washout ratio (RPW) obtained from unenhanced and triphasic enhanced CT (200 s delay) in distinguishing adrenal adenomas from non-adenomas,

Adrenal wash-out CT: moderate diagnostic value in distinguishing benign from malignant adrenal masses

“…In our series, we can confirm that all our pheochromocytomas presented unenhanced attenuation values >10 HU. A recent series from China with 116 adrenal masses (including 63 with unenhanced HU >10) suggested a short-time (200 s) delay wash-out CT ( 32 ). Although the authors claimed that this approach could help in differentiating adenomas from non-adenomas, there was significant overlap between groups and at least 10% of the non-adenoma group were misdiagnosed.…”

“…The ROC analysis for unenhanced CT revealed AUC of 0.89 (95% CI 0.85-0.93) for all lesions and of 0.76 (0.68-0.84) for the subgroup. At a threshold of ≤ 10HU, the sensitivity, specificity, PPV and NPV to diagnose a benign lesion were 54% (47-61), 100% (93-100), 100% (100-100) and 35% (31)(32)(33)(34)(35)(36)(37)(38). Using a cutoff of ≤ 20HU these values were 73% (66-79), 95.9% (86-100), 99% (95-100) and 46% (40-52), respectively, and two (potentially) malignant tumors (one metastasis of a lung cancer and one pheochromocytoma) were missed.…”

Adrenal Mass Characterization in the Era of Quantitative Imaging: State of the Art

“…The 10-min delayed acquisition yields a lower accuracy than 15 min and may require confirmation with a 15 min acquisition if negative [21]. A cutoff of 60% for APW yielded 88% sensitivity and 89% specificity of differentiating between lipid-poor AA and non-adenoma lesions, and a cut-off of 40% for RPW yielded 100% sensitivity and 100% specificity [22,23]. Finally, a subset of non-AA lesions with varying malignant potential are incompletely characterized using conventional imaging and require further investigation for a definite diagnosis [10].…”

Adrenal Lesions: A Review of Imaging

“…An absolute washout greater than or equal to 60% has a sensitivity of 86–94% and a specificity of 92–96% for the diagnosis of adrenal adenoma. Accordingly, a relative washout greater than or equal to 40% reported a sensitivity of 96% and a specificity of 100% for the diagnosis of adenoma [ 7 , 23 , 24 ].…”