Role of non contrast CT imaging

1-Size of the lesion: Lesions greater than 4 cm in diameter tend to be either metastases or primary carcinoma.

2-Change in lesion size: Adenomas are slow growing and tends not to increase in size.

3-Shape of the gland: Adenomas tend to have smooth margins and homogenous texture while malignant lesions tend to have irregular margins and heterogenous texture.

All the above signs are considered to be non specific.

4-Adenomas have abundant intracytoplasmic fat in the adrenal cortex and thus have low attenuation at CT (Fig).

Typical nonenhanced CT findings of an adrenal adenoma in a 64-year-old man with no known malignancy. The left adrenal adenoma (arrow) has smooth margins, is well defined, and has a attenuation of 5 HU, all findings characteristic of an adenoma.

5- Conversely, metastases have little intracytoplasmic fat and thus do not have low attenuation at nonenhanced CT (Fig).

Typical nonenhanced helical CT findings of metastasis in a 76-year-old man with lung carcinoma. On the CT scan, the right adrenal gland (arrow) is enlarged, has irregular contours, and has an attenuation of 36 HU, all findings characteristic of metastasis. Adrenal masses with attenuation values over 10 HU at nonenhanced CT require further evaluation with either CT contrast material washout, chemical shift MR imaging, or adrenal biopsy.

6- To differentiate a benign adenoma from a metastasis in the oncology patient, nonenhanced CT should be performed and attenuation of the mass quantified. If the attenuation of the adrenal mass is 10 HU or less, the mass is an adenoma and the work-up can stop. If the attenuation is over 10 HU, contrast-enhanced CT should be performed and washout calculated.