Adrenal cysts are rare lesions that are usually found incidentally on imaging performed for other reasons.
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Epidemiology
Adrenal cysts are reported to be rare with an incidence of <1% 1.
Clinical presentation
Patients can present with pain or swelling, although a significant portion (~40%) are incidental findings 1,3. Functional adrenal cysts are very rare 7.
Pathology
Adrenal cysts can be divided into four categories 1-3:
- pseudocysts
- endothelial cysts
- epithelial cysts
- including adult polycystic kidney disease (single case report) 4
- parasitic cysts, usually hydatid
Radiographic features
US
Usually thin-walled cystic lesions with anechoic content and posterior beam enhancement. Internal mobile echoes might be seen.
CT
Small adrenal cysts may be difficult to differentiate from adrenal adenomas on unenhanced CT as they may both have densities in the pure fluid range, i.e. -10 to +10. However on post-contrast CT adrenal adenomas tend to enhance, whereas cysts do not 5.
MRI
MRI is commonly reserved for those equivocal cases on CT and confirms fluid within the cyst (bright T2 signal) 6.
History and etymology
In 1966, the pathologist Dale G Foster subclassified adrenal cysts into four main types based on histopathological evaluation of 115 cases: epithelial cysts, parasitic cysts, especially hydatid, pseudocysts and endothelial cysts. In this series, endothelial cysts were the commonest type. Although other studies since have found pseudocysts to be more common 7.
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