For the diagnosis of adenoma versus metastasis, contrast- enhanced MRI does not provide additional information beyond the unenhanced technique. However, MRI without and with IV contrast may be considered if there is concern for pheochromocytoma or hypervascular metastasis, as the contrast can show the typical bright enhancement of this lesion. Contrast can also confirm lack of enhancement of a cystic lesion. 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. FDG-PET/CT Skull Base to Mid-Thigh FDG-PET can be used to identify metastases in oncologic patients in various cancers [26,77-79]. FDG-PET is sensitive to metabolically active lesions, and metastases usually show greater uptake than benign lesions. In several studies, there have been a few false-positives with FDG-PET, lowering specificity to 85% in one study [80], but excellent sensitivity has been achieved [26,77-79]. False-negative scans have occurred in renal cell carcinoma metastases [64]. SUVs are typically greater for metastatic disease [21]. However, mild activity can be seen in benign adenomas (typically less than background liver), thus potentially leading to false-positive interpretations. Studies have predominantly evaluated FDG-PET or FDG-PET/CT in the oncologic population. However, Tessonnier et al [44] evaluated 41 adrenal tumors in 37 patients who had no history of malignancy using FDG-PET/CT. All tumors were without diagnostically benign features on CT or MRI. In this small series, a tumor/liver SUVmax ratio >1.8 yielded 100% sensitivity and specificity for malignancy. 11C-metomidate has been found to localize in adrenocortical tumors and is useful for determining whether a tumor is of adrenocortical origin.
Adrenal Mass Evaluation. For the diagnosis of adenoma versus metastasis, contrast- enhanced MRI does not provide additional information beyond the unenhanced technique. However, MRI without and with IV contrast may be considered if there is concern for pheochromocytoma or hypervascular metastasis, as the contrast can show the typical bright enhancement of this lesion. Contrast can also confirm lack of enhancement of a cystic lesion. 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. FDG-PET/CT Skull Base to Mid-Thigh FDG-PET can be used to identify metastases in oncologic patients in various cancers [26,77-79]. FDG-PET is sensitive to metabolically active lesions, and metastases usually show greater uptake than benign lesions. In several studies, there have been a few false-positives with FDG-PET, lowering specificity to 85% in one study [80], but excellent sensitivity has been achieved [26,77-79]. False-negative scans have occurred in renal cell carcinoma metastases [64]. SUVs are typically greater for metastatic disease [21]. However, mild activity can be seen in benign adenomas (typically less than background liver), thus potentially leading to false-positive interpretations. Studies have predominantly evaluated FDG-PET or FDG-PET/CT in the oncologic population. However, Tessonnier et al [44] evaluated 41 adrenal tumors in 37 patients who had no history of malignancy using FDG-PET/CT. All tumors were without diagnostically benign features on CT or MRI. In this small series, a tumor/liver SUVmax ratio >1.8 yielded 100% sensitivity and specificity for malignancy. 11C-metomidate has been found to localize in adrenocortical tumors and is useful for determining whether a tumor is of adrenocortical origin.