What other types of adrenal gland nodules may contain microscopic lipid or macroscopic fat?
Adrenal gland metastases from clear cell renal cell carcinoma (RCC) or hepatocellular carcinoma (HCC) may rarely contain microscopic lipid, potentially mimicking adrenal adenomas. However, these usually occur in the setting of known malignancy and tend to grow over time. ACC may also contain microscopic lipid, but this is a rare tumor which tends to be large in size and heterogeneous in appearance, and thus easily distinguished from an adenoma.
Occasionally, small amounts of macroscopic fat may be seen within adrenal cortical neoplasms including degenerated adrenal adenomas and ACC secondary to myelolipomatous metaplasia, potentially mimicking adrenal myelolipomas. However, these tend to be more heterogeneous in appearance and are often large in size.
Finally, collision tumors of the adrenal gland may very rarely be encountered, where a malignant adrenal neoplasm such as by a metastasis or an ACC occurs in the setting of a preexisting adrenal adenoma or myelolipoma. In this setting, portions of the adrenal gland may contain microscopic lipid or macroscopic fat, whereas others do not.
Thus, if a lipid- or fat-containing adrenal gland nodule is large (>3 to 4 cm) in size, grows in size, or is heterogeneous in appearance, then a follow-up CT or MRI scan is generally warranted to exclude these other less common etiologies which may mimic the appearance of adrenal adenomas and myelolipomas.