الفهرس 
ANATOMY OF ADRENAL GLANDOnly 14 pages are availabe for public view
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Abstract
PET/CT offers a unique hybrid imaging technique that combines the attenuation and morphologic detail of CT with the metabolic information from PET. These images can be fused to allow accurate coregistration of anatomic and functional data.
Adrenal PET-CT allows determination of the attenuation characteristics and the metabolic activity of adrenal lesions with a single examination and, in the majority of cases, should provide information that is diagnostic. The characterization of adrenal lesions with FDG PET depends on increased glucose metabolism in malignancy. Lesions with activity that is less or much greater than that of the liver can confidently be diagnosed as benign or malignant, respectively lesions with slightly increased activity relative to the liver are classified as indeterminate. Authors have reported up to 100% sensitivity and specificity for FDG PET in distinguishing benign from malignant lesions.
Metastases to the adrenal glands are common and can have a variety of appearances at CT. Up to 50% of adrenal masses in patients with known malignancy may be benign ;thus, non-invasive characterization is important in preventing unnecessary biopsy.
Adenomas usually do not show abnormally increased FDG activity, although there have been reports of false-positive moderate FDG uptake Why some adenomas show relatively increased FDG uptake remains unclear.
Adrenal lesions that show equivocal increased activity can be further characterized with the CT component of the PET-CT examination ; one author has suggested incorporating delayed contrast-enhanced CT for washout analysis as a useful adjunct in characterizing lipid-poor lesions. Because it makes use of the full capability of both modalities, fusion PET-CT can help characterize lesions as adrenal adenomas, particularly those that are deemed indeterminate with CT or PET alone.
Hypermetabolic lesions do not always indicate malignancy. In general, false-positive FDG uptake can occur at PET-CT due to granulomatous disease, abscess, surgical changes, foreign body reaction, or inflammation (e.g., in diverticulitis, gastritis, or arteriosclerosis) .
False-positive findings may occur at adrenal FDG PET, particularly with respect to pheochromocytoma and adrenal hyperplasia, although approximately 5% of adenomas and, rarely, myelolipomas may also yield false-positive findings.
False-negative PET findings can result if tumors are either too small or non -FDG avid. The latter group includes some neuroendocrine tumors, renal cell carcinoma (RCC), and certain types of lymphoma, although most lymphomas are FDG avid. High neighboring background activity can also obscure FDG uptake.
In conclusion, PET-CT combines complementary modalities, thereby allowing precise structural and functional characterization of a variety of conditions affecting the adrenal gland, with subsequent significant impact on clinical management. A variety of pitfalls are inherent in the use of either modality alone, so that combined PET-CT provides added diagnostic value. However, PET-CT also has certain limitations. Benign entities (eg, lipid-poor adenomas) may show increased uptake at FDG PET and may be indeterminate at standard CT. Moreover, the combined information from PET-CT, although often useful, will not always obviate additional studies or biopsy.