18F-FDG PET/CT characterization of adrenal lesions and its multimodality correlation.

2028 Objectives: To evaluate spectrum of characteristic findings and patterns of FDG uptake in adrenal lesions on routine oncologic 18F-FDG PET/CT. To correlate 18F-FDG PET/CT findings with other imaging modalities. Methods: 18F-FDG PET/CT is useful in evaluation of adrenal lesions; however some benign lesions demonstrate FDG uptake leading to inaccurate interpretation. We present a case based pictorial review highlighting varying degree of FDG uptake and its multimodality correlation in a spectrum of adrenal lesions including adrenal adenoma, hyperplasia, myelolipoma, pheochromocytoma, lymphoma, metastasis, calcifications, and adrenocortical carcinoma. Adrenal adenoma is a common benign adrenal cortical tumor which may be functional or nonfunctional. Approximately 70% of adenomas demonstrate unenhanced CT attenuation of 10. Unlike PET; other imaging modalities such as CT or MRI cannot differentiate hyper functioning from non-hyper functioning adenomas. FDG avidity of adrenal adenoma is usually less than the hepatic background with lipid rich and lipid poor adenomas demonstrating no significant difference in SUVmax. Adrenal hyperplasia is one of the causes of Cushing Syndrome. ACTH-independent Cushing syndrome is due to cortisol secreting primary adrenal disease such as adrenal adenoma, carcinoma, and rarely by primary pigmented nodular adrenal dysplasia and ACTH-independent macronodular adrenal hyperplasia. On 18F-FDG PET/CT, adrenal hyperplasia can show diffuse or nodular adrenal enlargement with mild to moderate FDG uptake. Adrenal myelolipoma is a benign tumor with fat and interspersed hematopoietic cells. CT imaging characteristics include a well-defined adrenal mass with pseudo capsule and internal mixed fat and high-attenuation contents. Hyperdensity in larger myelolipomas is most suggestive of hemorrhage. Myelolipomas typically show FDG uptake lower than that of the hepatic Background: In rare cases, adrenal myelolipomas with extensive adenomatous and hematopoietic elements may demonstrate high FDG uptake. Pheochromocytoma on CT/MRI characteristically appears as a hyper vascular adrenal mass with marked contrast enhancement. Significant/intense FDG uptake is seen in malignant pheochromocytomas as compared to benign pheochromocytomas. Non-Hodgkin lymphoma can involve the adrenal glands (usually bilateral) and shows intense FDG avidity. The glands usually return to their normal size with resolution of FDG avidity. Adrenal glands are one of the common site of metastasis and is usually seen with primary malignancy of lung, stomach, hepatic and gastrointestinal tract. Adrenal metastasis usually shows FDG uptake higher than that of the liver Background: Adrenal calcifications are usually non FDG avid and likely sequelae of prior infection/ hemorrhage. However, should be differentiated from intra lesional calcifications in an enhancing mass. Conclusion:18F-FDG PET/CT is useful in evaluation of different adrenal lesions; however some benign lesions also demonstrate FDG avidity. It is difficult to differentiate benign lesions from malignant lesions on 18F-FDG PET/CT alone and should be correlated with patient’s clinical history, laboratory results and other modalities like MRI. The presented PET CT case based pictorial review raises awareness and strengthens the judgement of the reading physician.