Adrenal metastasis

Adrenal metastases are the most common malignant lesions involving the adrenal gland. Metastases are usually bilateral but may also be unilateral. Unilateral involvement is more prevalent on the left side (ratio of 1.5:1).

Epidemiology

They are present at autopsy in up to 27% of patients with known malignant epithelial tumors.

Pathology

Primary sites

Many primary tumors can potentially metastasize to the adrenal glands, commonly:

• lung cancer
• colorectal carcinoma 
• breast cancer
• pancreatic cancer 

Other reported primary tumors include:

• renal cell carcinoma (RCC)
• hepatocellular carcinoma (HCC) ³
• malignant melanoma
• endometrial adenocarcinoma ⁷
• ovarian carcinoma ⁸
• prostatic cancer ⁹
• gastric cancer ¹⁰
• cholangiocarcinoma ¹¹
• esophageal adenocarcinoma ¹²
• bladder carcinoma ¹³
• osteogenic osteosarcoma (rare) ¹⁴
• papillary thyroid carcinoma (rare)¹⁵
• testicular cancer ¹⁶

Radiographic features

CT

Adrenal metastases can have variable CT appearances ⁴. They usually demonstrate <50% washout.

In patients with RCC and HCC who undergo dedicated adrenal CT imaging for known adrenal lesions, the enhancement washout of adrenal metastases can be similar to that of lipid-poor adrenal adenomas. As hypervascular lesions, they commonly show intense enhancement on the portal venous phase, usually more than 120 HU, and thus can be easily identified. 

MRI

Exact signal characteristics can vary depending on the type of tumor. In general, commonly described signal characteristics include:

• T1: usually exhibit low signal intensity ²
• T2:  often show high signal intensity ²
• T1 C+ (Gd): usually has progressive enhancement after administration of contrast material ²

An important diagnostic feature is the lack of signal loss on out-of-phase images (in contradistinction to that seen with adrenal adenoma).

Practical points

• on CT, metastases usually demonstrate <50% washout
• if intense enhancement of >120 HU is identified in the portal venous phase, washout should be ignored, and a hypervascular lesion such as RCC or HCC metastasis should be considered as a primary
• MRI: no signal loss on out-of-phase images