From the Guidelines
Normal adrenal glands on contrast-enhanced CT typically measure between 10-40 Hounsfield Units (HU). The most recent and highest quality study, 1, published in 2023, confirms that a mass with homogeneous, well-circumscribed features and measures <10 HU in attenuation can be confidently diagnosed as benign. Key characteristics of normal adrenal glands on CT include:
- Rapid enhancement after intravenous contrast administration
- Washout over time, with an absolute percentage washout of greater than 60% on delayed images (typically at 15 minutes)
- Inverted Y or V-shaped structures in the suprarenal region
- Thickness of less than 10 mm in the body and limbs Understanding these normal density values is crucial for differentiating between normal adrenal tissue and pathological conditions, such as adrenal adenomas, malignant lesions, and pheochromocytomas, which demonstrate different enhancement patterns and attenuation values 1.
From the Research
Normal Hounsfield Units for Adrenal Gland on Contrast-Enhanced CT
- The normal Hounsfield units (HU) for an adrenal gland on a contrast-enhanced CT scan can vary, but studies suggest that a threshold of ≤ 10 HU is often used to identify adrenal adenomas on unenhanced CT scans 2.
- However, using a threshold of ≤ 10 HU may miss 10-40% of benign adenomas, and adjusting the threshold to ≤ 16 HU may improve sensitivity without reducing specificity 2.
- It's essential to consider that HU measurements can vary over time, between scanners, and between observers, which can affect the evaluation of adrenal lesions 3.
- A study found that mean adrenal lesion non-enhanced attenuation values decreased by 0.5 HU/year during follow-up, and using specific attenuation threshold values for characterizing adrenal lesions must be done with caution 3.
Characterization of Adrenal Lesions
- Adrenal lesions can be characterized as benign or malignant based on their radiological features, and CT and MRI are commonly used imaging modalities for this purpose 4, 5, 6.
- Benign lesions include adenoma, hyperplasia, pheochromocytoma, cyst, hemorrhage, and myelolipoma, while malignant lesions include metastases, adrenal cortical carcinoma, and neuroblastoma 4, 5.
- The use of contrast-enhanced CT scans and MRI can help differentiate between benign and malignant lesions, and established morphologic criteria can be used to assess whether an adrenal mass is benign or malignant 6.