SIU 2017: American Urological Association Lecture - Adrenal Imaging: A Urologist’s Perspective
Adrenal incidentalomas are defined as an adrenal mass > 1 cm incidentally seen in an asymptomatic patient with no known malignancy. They occur in about 5% of the population and increase with age to 7% at age 70. 10-15% of cases are bilateral. Fortunately, 90% of these masses are benign with no reports of transformation. Anytime an adrenal mass is witnessed, we have two goals to perform:
1) exclude a functioning lesion, through lab testing
2) exclude cancer through the use of imaging – which will be the main focus of this presentation
There are 3 important imaging modalities we need to be aware and master. The most important one is the CT scan of the adrenal, which must show us thin slices of 3 mm or less, must start with an unenhanced phase and include a phase post IV contrast administration, occurring at least one minute and 15 seconds after contrast injection.
Adrenal adenomas have 2 characteristic features:
1) 80% of them are lipid rich demonstrating a low density (in HU) in the CT
2) These lesions will enhance rapidly and also wash out rapidly, which is in contrast to malignant adrenal lesions, which wash out very slowly
Therefore, any lesion with a density of less than 10 HU in the unenhanced scan, regardless of size, are 100% adenoma, and no contrast phase is needed. If the mass is between 10-20 HU (or more) on the unenhanced scan – the IV contrast phase must be done. At this phase the radiologist measures the absolute and relative washouts. An adenoma is diagnosed if more than 60% absolute or more than 40% relative washout occur. This test has a sensitivity of 90-95% and specificity of 95%-100%.
Adrenocortical carcinoma and pheochromacytoma tumors will show more than 30 HU at the unenhanced phase. Additionally, they manifest bright enhancement, they are heterogeneous, demonstrating local invasion, and usually being of large size, with occasional accompanying tumor thrombus. Size in adrenal masses does matter, and today we know that above 6 cm, the mass definitely needs to be removed.False positive results are seen in inflammatory lesions and some benign adenomas. False negative lesions can be seen with very small metastasis, lesions less than 10 mm, lesions with significant necrosis /hemorrhage, and be non-FDG avid cancer – such as Broncho-alveolar carcinoma, carcinoid and renal cell carcinoma,
Adrenocortical carcinomas are usually large (10-15 cm) with no decrease in size with increased imaging. Two thirds of them are usually symptomatic due to hormone secretion. It is a rare tumor with data in the US showing that there have been 4200 cases in the entire country from 1985-2007. Surgery is the only real cure for this disease.
There are newer CT techniques that are being evaluated. This includes dual CT and CT perfusion imaging techniques, that have thus far not shown a real advantage over regular standard CT.
Adrenal MRI is used less commonly than CT. It is mainly used in patients who cannot tolerate radiation such as children and pregnant women. It can also be used when CT results are equivocal, especially in lipid poor adenomas. The MRI is usually used in the modality of the T1 weighted MRI. Newer MRI techniques are continuously being explored with no significant advantage on regular MRI witnessed so far.
The FDG PET scan is not a superior imaging modality to adrenal masses and it has been shown not to be superior to CT or MRI scans. It is especially useful for identifying metastatic lesions and best when the primary tumor is known to be FDG avid.
Adrenal metastasis are most commonly from lung, breast, kidney, ovary, and melanoma. It usually manifests as a new onset adrenal mass in a patient with a history of cancer. Occasionally, it is the only metastasis, and it is the only good indication for a percutaneous biopsy. It is reasonable to excise surgically, like a normal adrenalectomy.
Cystic adrenal lesions are not common. They are similar to renal cystic lesions. Simple cysts are usually benign. Cystic tumors are usually with thick enhancing wall, and mural nodules.
Dr. Fergany summarized and stated, that imaging is primarily used to exclude or diagnose malignancy. Adrenal CT is the primary study. Surgery is usually recommended by size alone and not 100% accurate. Biopsy should be reserved for metastasis, and PET scans are not better than standard CT or MRI.
Speaker: Amr Fergany, United States
Written by: Hanan Goldberg, MD, Urologic Oncology Fellow (SUO), University of Toronto, Princess Margaret Cancer Centre, @GoldbergHanan, at the 37th Congress of Société Internationale d’Urologie - October 19-22, 2017- Lisbon, Portugal