Adrenal Adenomas versus Metastases: Diagnostic Performance of Dual-Energy Spectral CT Virtual Noncontrast Imaging and Iodine Maps

Abstract

GASTROINTESTINAL IMAGINGG iven the extensive use of medical cross-sectional imaging, the incidental detection of adrenal lesions has concomitantly increased, occurring in approximately 5%-8% of patients undergoing CT (1-5). Although most incidental adrenal lesions are benign adenomas, the most common clinical dilemma has been the differentiation between adenomas and metastases, particularly among patients with a history of extra-adrenal malignancy (1-3). Because the presence of metastasis can affect treatment strategies and patient prognosis, accurate and noninvasive discrimination between the two entities is critical.Adrenal adenomas have two key CT imaging features: (a) low unenhanced attenuation reflecting intracytoplasmic fat content and (b) maximized contrast enhancement during the portal venous phase followed by rapid washout during the delayed phase (5)(6)(7)(8)(9)(10)(11)(12). Approximately 70% of adenomas can be diagnosed as lipid-rich adenoma based on unenhanced attenuation (10 HU) (5-8), whereas most lipid-poor adenomas (.10 HU) can be diagnosed based on the high washout rate calculated at multiphasic adrenal CT (7-12

Relative Enhancement Ratio of Portal Venous Phase to Unenhanced CT in the Diagnosis of Lipid-poor Adrenal Adenomas

“…In our study, lipid-poor adenomas showed a lower unenhanced attenuation than nonadenomas (22 HU 6 6 vs 34 HU 6 7; P , .001), as in previous studies (5,(9)(10)(11)(12)(19)(20)(21)(22). Additionally, the absolute enhancement of adenomas was 1.5-fold higher than nonadenomas (P , .001), which is also corroborated by data from numerous studies wherein adenomas had higher (up to 2.2-fold) absolute enhancement compared with nonadenomas, mostly comprising metastases (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)14,16,22,29,30) (Table E4 [online]). We introduced a new imaging parameter of relative enhancement ratio by combining unenhanced attenuation and absolute enhancement, yielding a diagnostic performance almost comparable with the previously reported washout CT (sensitivity, 86% vs 82%-92%; specificity, 95% vs 87%-100%) for the discrimination of lipid-poor adenomas (5,9,10,21).…”

“…In this study, adrenal metastases from hepatocellular carcinoma (HCC), renal cell carcinoma (RCC), pheochromocytomas, and adrenocortical carcinomas were categorized as hypervascular nonadenomas, which reportedly mimic adenomas at contrast-enhancement CT (19,(23)(24)(25)(26)(27)(28). In a prior study (29) on contrast-enhanced dual-energy CT that evaluated the diagnostic performance of virtual noncontrast attenuation and iodine density for differentiating adrenal adenomas from metastases, we reported on 36 patients included in the current study. All CT images were acquired at different times and with use of different scanners than those in the prior study.…”

“…A total of 29 relevant articles from the literature were reviewed (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(14)(15)(16)19,20,(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34). Sixteen studies provided data on both adenomas (n = 964) and nonadenomas mostly comprising metastases (n = 623), all of which showed higher absolute enhancement in adenomas than in nonadenomas (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)14,16,22,29,30) (Table E4 [online]).…”

“…A total of 29 relevant articles from the literature were reviewed (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(14)(15)(16)19,20,(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34). Sixteen studies provided data on both adenomas (n = 964) and nonadenomas mostly comprising metastases (n = 623), all of which showed higher absolute enhancement in adenomas than in nonadenomas (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)14,16,22,29,30) (Table E4 [online]). Of the 13 articles providing data on both adenomas and hypervascular nonadenomas, 10 studies (759 adenomas vs 234 pheochromocytomas, 56 adrenocortical carcinomas, and 24 metastases from RCC or HCC) showed higher or equivalent absolute enhancement in adenomas than in hypervascular nonad- Note....…”

Spectral Imaging With Dual-layer Spectral Detector Computed Tomography for Acute Coronary Syndrome

“…However, no studies have reported the usefulness of rest cardiac DECT for ACS. Recently, dual-layer DECT (DL-DECT) has been introduced for clinical use [11][12][13]. DL-DECT can overcome the disadvantage of increased image noise at low-energy levels.…”