Imaging of Cushing Syndrome What X-rays (scans) is used for imaging of adrenal tumors in overt and subclinical Cushing syndrome? In cases in which the biochemical diagnosis of ACTH-independent Cushing syndrome has been established, attention can be turned to imaging the adrenal gland with computed tomography (CT) or magnetic resonance imaging (MRI) to lateralize the source of cortisol hypersecretion. You can read more about adrenal imaging here. When we look at the imaging of the adrenal gland whether it is a Ultrasound, CT, MRI, Nuclear Medicine (MIBG, PET, etc) scan or other imaging study we need to have a whole-person approach and evaluate all aspects of the tumor and the patient. We carefully analyze the imaging phenotype of the tumor. The imaging phenotype describes all the aspects of what the tumor looks like on your scan and helps us arrive as the correct diagnosis including the likelihood of cancer. Key points with adrenal imaging are: • A benign adrenocortical adenoma is the most common adrenal tumor • The gold standard of adrenal imaging is a CT scan (CAT scan). An “adrenal-protocol, contrast enhancement CT scan” is best. • MR imaging is sometimes useful as an adjunct. • Nuclear medicine techniques are helpful in some specific settings Ultrasound This is the fastest, cheapest, and most readily available test to look at the kidneys and adrenals. But it is the least accurate, so it is usually not used as much as the CT scan. It can be used to examine any type of adrenal tumor. CT Scan The CT scan (also called CAT scan) is very accurate at examining the adrenal glands and other abdominal structures and can be used on any type of adrenal tumor. Like the other 3 tests in this group, the CT scan is painless. It will take only a few minutes to complete. The pictures which result are very good at finding tumors throughout the body, and very accurate measurements can be taken which help the planning of subsequent therapies. CT represents the first-level imaging modality for the evaluation of adrenal lesions, since it permits a quick execution ensuring high spatial resolution, with findings of pre-contrast images and post-contrast behavior being commonly used to achieve a correct diagnosis. An “adrenal-protocol, contrast enhancement CT scan” is best. At unenhanced (no contrast) CT, adenomas are usually well-demarcated round or oval lesions, with homogeneous and relatively low attenuation values (lower than 10 Hounsfield Units [HU]), due to high fat content. However, unenhanced CT alone is not always diagnostic since 15–30% of adenomas are lipid-poor, thereby showing higher attenuation values. In these cases, additional imaging after intravenous contrast administration (adrenal-protocol, contrast enhancement CT scan) is required to differentiate adenoma from non-adenomas. Adrenocortical carcinoma displays heterogeneous (variable) appearance due to necrosis, calcifications, and hemorrhage (previous bleeding into the tumor). After intravenous contrast injection, it demonstrates heterogeneous and mainly peripheral enhancement. The RPW of the carcinoma tends to be less than 40%. Invasion of adjacent structures such as kidney, inferior vena cava, liver, pancreas, spleen and splenic vessels are may occur as well as liver metastasis and retroperitoneal lymph nodal locations. MRI Scan The MRI (also called an MR scan or NMR scan) is very similar to the CT scan in the type of information and pictures it provides. The scan takes about an hour and uses magnetic fields to generate pictures of body structures rather than x-rays like the CT scan or sound waves like the ultrasound. MRI has similar diagnostic accuracy to CT allowing characterizing adenomas regardless of their CT enhancement. On T2-weighted MR images (fluid filled tissues appear bright), adrenal aden- omas are homogeneous and present intermediate-low signal intensity compared to skeletal muscle or liver. An important component of adrenal MRI protocol is chemical shift imaging (CSI). This modality enables the radiologist to detect intra-tumor fat resulting in a loss of signal intensity. The MR sensitivity for adenomas measuring 10–20 HU is nearly 100%, while that for lipid-poor adenomas measuring greater than 30 HU is significantly lower (13–75%) On MR, adrenocortical carcinoma shows low signal intensity on T1-weighted images, high signal on T2-weighted images, and strong and heterogeneous contrast enhancement with slow washout. Similarly, metastasis to the adrenal gland can appear very variable on an MRI scan. Nuclear Medicine Scans A nuclear medicine scan uses radioactive substances (very low radiation dose) to take pictures of areas inside the body. The radioactive substance is injected into the body, and locates and binds to specific cells or tissues, including cancer cells. Regular PET (18-FDG-PET/CT) is mainly used to image malignant (cancerous lesions), so when it comes to cortisol-producing adrenal tumors it is mainly used if adrenocortical cancer-causing Cushing syndrome is suspected.