Incidental Adrenal Nodule in a Patient with Resected Melanoma
A 62-year-old man with a history of stage IIB melanoma of the left shoulder resected 3 years ago presents for routine surveillance. He feels well and has no symptoms. A CT of the chest, abdomen, and pelvis with IV contrast is performed. It reveals a 2.5 cm homogeneous, well-defined left adrenal nodule with a pre-contrast attenuation of 15 HU. The nodule enhances with contrast. There is no other evidence of metastatic disease. His blood pressure is 128/78 mmHg, and he takes no medications. Laboratory studies show normal electrolytes and renal function. The patient is concerned about the possibility of metastasis and asks what the next step is.
1. How would you characterize this adrenal nodule, and what is the appropriate next imaging step?
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The adrenal nodule is 2.5 cm, homogeneous, and has a pre-contrast attenuation of 15 HU. A threshold of ≤10 HU on unenhanced CT is highly specific for a benign lipid-rich adenoma; however, this nodule measures 15 HU, which is indeterminate. The patient has a history of melanoma, which is known to metastasize to the adrenal glands. Therefore, the nodule cannot be assumed benign. The next step is to perform a dedicated adrenal protocol CT, which includes unenhanced, enhanced, and delayed (15-minute) imaging to calculate the absolute and relative washout. If the nodule demonstrates absolute washout >60% or relative washout >40%, it is likely a benign adenoma. If washout is indeterminate or low, further evaluation with PET/CT or biopsy should be considered. Alternatively, MRI with chemical shift imaging can be used to detect intracellular lipid. Given the melanoma history, a PET/CT may be particularly useful to assess for other sites of metastasis and to characterize the adrenal lesion. The patient should be referred to oncology for discussion.
2. The adrenal protocol CT shows an absolute washout of 35% and relative washout of 20%. What is the interpretation, and what are the management options?
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An absolute washout of 35% and relative washout of 20% are below the thresholds for a benign adenoma (absolute washout >60%, relative washout >40%). This indeterminate washout pattern raises concern for a non-adenomatous lesion, including metastasis, pheochromocytoma, or adrenocortical carcinoma. Given the history of melanoma, metastasis is a significant concern. Management options include: (1) PET/CT with FDG to assess metabolic activity and screen for other metastases; (2) image-guided percutaneous biopsy, although biopsy of the adrenal gland carries a small risk of bleeding and is generally avoided if the lesion is resectable and the patient is a surgical candidate; (3) surgical resection if the lesion is isolated and the patient is fit. A multidisciplinary approach with oncology, surgery, and radiology is recommended. Biochemical evaluation for pheochromocytoma (plasma metanephrines) should be considered before any biopsy or surgery to avoid hypertensive crisis. If the lesion is solitary and resectable, adrenalectomy may be both diagnostic and therapeutic.