Adenomas
The most common primary adrenal tumour; incidence increases with age.
Diagnosis and evaluation — the vast majority (93%) are metabolically silent. The essential task in evaluating a small adrenal mass is to differentiate the non-functional benign adenoma from functional or malignant lesions.
Management:
- Functional adenoma — should undergo resection in an acceptable surgical candidate.
- Non-functional adenoma — size and growth characteristics dictate management (as described in the adrenal-mass work-up). Adenomas that are initially metabolically inert are unlikely (<2%) to gain function; despite this low rate of "metabolic transformation," the most recent NIH-convened consensus statement suggests that annual metabolic hormonal screening for the first 3–4 years after diagnosis is prudent.
Oncocytoma
Extremely rare. Although predominantly benign, a proportion can exhibit malignant potential. On imaging, adrenal oncocytic lesions lack the central stellate scar often seen in renal oncocytomas. Because the diagnosis is nearly always made on surgical resection, evaluation and treatment follow the same strategy as that of other adrenal masses.
Myelolipoma
Rare, benign, metabolically silent lesions with tissue components identical to healthy bone marrow. In most cases, diagnosis can be made accurately on cross-sectional imaging — usual CT enhancement is between -30 and -140 Hounsfield units. The NIH consensus panel on adrenal incidentaloma concluded that myelolipoma can be regarded as an exception to the mandatory metabolic work-up of a newly discovered adrenal mass. Classically asymptomatic myelolipomas are treated conservatively; surgery is indicated only for extremely large or symptomatic lesions.
Ganglioneuroma
Extremely rare benign neuroectodermal neoplasms that tend to occur in the young and are composed of ganglion and Schwann cells. They can grow extremely large and have a propensity to encase vessels without impinging on the vessel lumen.
Cysts
Four types of adrenal cyst have been described: pseudocysts, endothelial cysts, epithelial cysts, and parasitic cysts. 7% of adrenal cysts are associated with malignancy — all of which were pseudocysts — so observation must be done with caution. Although the majority of adrenal cysts are benign and non-functional, routine endocrinologic evaluation should be performed to exclude active lesions.
Self-Test
1. What is the histology of the most common primary adrenal tumour? Adenoma.