For patients with a history of malignancy and an adrenal mass >1 cm and <4 cm and no diagnostic benign imaging features on prior examinations or documented stability, adrenal-specific imaging should be performed. If adrenal- specific imaging does not characterize the lesion as benign or if the results are indeterminate, evaluation of other imaging features, such as presence of central necrosis and presence of irregular margins or thick enhancing rim, can indicate an increased likelihood of malignancy [74]. In these instances, adrenal biopsy or FDG-PET/CT should be considered for further evaluation [75]. In patients with a history of malignancy, Candel et al [11] found that 87% of lesions <3 cm were benign and that >95% of lesions >3 cm were malignant. In a similar population, Lee et al [35] found that 79% of lesions <2.5 cm were benign. Van Erkel et al [67] in a mixed population showed that a threshold of 3.1 cm discriminated 93% of lesions. CT Abdomen Evaluation of an adrenal mass indeterminate on initial imaging consists of an adrenal CT protocol. Unenhanced thin-section images through the upper abdomen are obtained and then reviewed to evaluate for diagnostic benign imaging features. Some benign lesions, such as cysts and myelolipomas, are readily characterized by CT. Adrenal adenomas contain lipid to varying degrees, and this lowers their attenuation coefficient on unenhanced CT. A threshold value of 10 HU is generally accepted as a cutoff value for diagnosing a lipid-rich adenoma, as the 10 HU threshold has a sensitivity of 71% and specificity of 98% for adenomas [34]. As the threshold value for HU unit cutoff is increased (for example from 0 to 10 HU), the sensitivity for adenomas increases; however, so does the false-positive rate [35,36]. Lesions that do not contain intracellular lipid (adenoma) or macroscopic fat (myelolipoma) on CT are evaluated with pre- and postcontrast imaging.
Adrenal Mass Evaluation. For patients with a history of malignancy and an adrenal mass >1 cm and <4 cm and no diagnostic benign imaging features on prior examinations or documented stability, adrenal-specific imaging should be performed. If adrenal- specific imaging does not characterize the lesion as benign or if the results are indeterminate, evaluation of other imaging features, such as presence of central necrosis and presence of irregular margins or thick enhancing rim, can indicate an increased likelihood of malignancy [74]. In these instances, adrenal biopsy or FDG-PET/CT should be considered for further evaluation [75]. In patients with a history of malignancy, Candel et al [11] found that 87% of lesions <3 cm were benign and that >95% of lesions >3 cm were malignant. In a similar population, Lee et al [35] found that 79% of lesions <2.5 cm were benign. Van Erkel et al [67] in a mixed population showed that a threshold of 3.1 cm discriminated 93% of lesions. CT Abdomen Evaluation of an adrenal mass indeterminate on initial imaging consists of an adrenal CT protocol. Unenhanced thin-section images through the upper abdomen are obtained and then reviewed to evaluate for diagnostic benign imaging features. Some benign lesions, such as cysts and myelolipomas, are readily characterized by CT. Adrenal adenomas contain lipid to varying degrees, and this lowers their attenuation coefficient on unenhanced CT. A threshold value of 10 HU is generally accepted as a cutoff value for diagnosing a lipid-rich adenoma, as the 10 HU threshold has a sensitivity of 71% and specificity of 98% for adenomas [34]. As the threshold value for HU unit cutoff is increased (for example from 0 to 10 HU), the sensitivity for adenomas increases; however, so does the false-positive rate [35,36]. Lesions that do not contain intracellular lipid (adenoma) or macroscopic fat (myelolipoma) on CT are evaluated with pre- and postcontrast imaging.