How to evaluate a 9mm adrenal nodule with a density of -2 Hounsfield Units (HU)?

From the Guidelines

A 9mm adrenal nodule with -2 Hounsfield units (HU) should be considered a benign adrenal adenoma that typically requires no further evaluation or follow-up. The negative HU value (-2) strongly indicates that this is a lipid-rich adenoma, as benign adrenal adenomas contain intracytoplasmic fat which produces characteristic low attenuation values (<10 HU) on non-contrast CT, as shown by studies such as 1. For adrenal nodules with HU values below 10 on non-contrast CT, the specificity for diagnosing a benign adenoma exceeds 95%, according to the findings of 1. The small size (9mm) further supports its benign nature, as adrenal malignancies are typically larger than 4cm at diagnosis, as discussed in 1. Some key points to consider in the evaluation of this adrenal nodule include:

• Size: The size of the nodule is an important variable in predicting malignancy, with smaller lesions being more likely to be benign, as noted in 1.
• Hounsfield units: The HU value of the nodule is a key factor in determining its likelihood of being benign or malignant, with values below 10 HU being more indicative of a benign adenoma, as shown in 1.
• Clinical features: If the patient has hypertension, electrolyte abnormalities, or clinical features suggesting hormonal excess, biochemical evaluation for functional adrenal disorders should be performed, regardless of the benign imaging characteristics. It is essential to consider the patient's overall clinical presentation and medical history when evaluating the adrenal nodule, as discussed in 1. In general, for patients with no histories of malignancy, most small (less than 3 cm) incidentally discovered adrenal masses are benign, and extensive and costly workup is usually not justified, as stated in 1. However, if there are any concerns or uncertainties, further evaluation and consultation with a specialist may be necessary to determine the best course of action.

From the Research

Evaluation of 9mm Adrenal Nodule with -2 Hounsfield Units

• The evaluation of adrenal nodules is crucial to determine whether they are benign or malignant 2.
• A 9mm adrenal nodule with -2 Hounsfield units is likely to be a benign adenoma, as most adrenal adenomas have a Hounsfield unit value of less than 10 3.
• However, the size of the nodule is also an important factor, and nodules larger than 4 cm are more likely to be malignant 2.
• In this case, the nodule is 9mm, which is less than 1 cm, and the Hounsfield unit value is -2, which suggests that it is likely to be a benign adenoma.
• The use of absolute percent contrast washout (APW) criteria may also be helpful in identifying adrenal adenomas, with an APW value of more than 60% suggesting a benign lesion 3.

Diagnostic Approach

• The diagnostic approach to adrenal nodules should focus on determining whether the lesion is malignant and whether it is hormonally active 2.
• Imaging studies, such as computed tomography (CT) and magnetic resonance imaging (MRI), can be used to evaluate the size and characteristics of the nodule 4, 5.
• Fine-needle aspiration (FNA) cytology may also be used to obtain a tissue diagnosis, especially in cases where the nodule is large or has suspicious features 4, 5.
• Hormonal evaluation, including tests for subclinical Cushing's syndrome and pheochromocytoma, should also be performed 2.

Management

• The management of adrenal nodules depends on the size and characteristics of the nodule, as well as the results of hormonal evaluation 2.
• Nodules larger than 4 cm or those with suspicious features should be surgically excised 2.
• Smaller nodules with benign characteristics can be monitored with regular imaging studies 2.
• The use of a combination of imaging studies and FNA cytology may be helpful in selecting patients for surgery 4, 5.