From the Guidelines
The best imaging for adrenal gland adenoma is a non-contrast CT scan with adrenal protocol, which can reliably diagnose these benign tumors based on their characteristic low attenuation values (typically less than 10 Hounsfield Units). This imaging technique takes advantage of the high lipid content in most adrenal adenomas, which appears as low density on CT 1. For indeterminate lesions on non-contrast CT, a contrast-enhanced CT with washout calculations can be performed, with adenomas typically showing rapid contrast washout (>60% at 15 minutes). However, it's essential to note that contrast-enhanced washout CT has limitations, including false positive and false negative rates, and roughly 1/3 of pheochromocytomas may washout in the characteristic range of an adenoma 1.
Some key points to consider when choosing an imaging modality for adrenal gland adenoma include:
- The clinical context, including the patient's age, symptoms, and whether the adrenal mass was incidentally discovered
- The availability of MRI with chemical shift imaging, which can detect microscopic fat within adenomas through signal loss on opposed-phase images compared to in-phase images 1
- The potential need for nuclear medicine studies, such as PET scans, to evaluate for functional activity or malignancy
It's also important to consider the role of biopsy in the work-up of an incidental adrenal lesion. Adrenal mass biopsy is rarely indicated, but may be considered when the diagnosis of metastatic disease from an extra-adrenal malignancy would be of value 1. Ultimately, the choice of imaging modality should prioritize the patient's safety and well-being, while also providing accurate diagnostic information to guide treatment decisions.
From the Research
Imaging Modalities for Adrenal Gland Adenoma
The best imaging modality for adrenal gland adenoma can be determined by considering the following factors:
- Computed Tomography (CT) is highly sensitive for detecting small adrenal tumors and adrenal hyperplasia 2
- Magnetic Resonance Imaging (MRI) is useful for characterizing adrenal masses that cannot be characterized using unenhanced CT 2
- MRI, particularly chemical shift imaging (CSI), can distinguish between benign and malignant lesions and is a first-choice imaging modality for patients like children or pregnant women 3
- Positron Emission Tomography (PET) using the tracer 11C-metomidate (MTO) has high sensitivity for identifying adrenocortical lesions and can be used as an additional imaging modality for further characterization 4
Comparison of Imaging Modalities
The following points compare the imaging modalities:
- CT has higher sensitivity for detection of small adrenal tumors and adrenal hyperplasia than MRI 2
- MRI has higher specificity for characterizing adrenal masses than CT 4
- The combination of CT, MRI, and MTO-PET can provide maximum sensitivity and specificity for adenoma characterization 4
- The choice of imaging modality depends on the specific clinical scenario and patient population, such as children or pregnant women 3
Diagnostic Accuracies and Differential Diagnoses
The diagnostic accuracies and differential diagnoses of adrenal gland adenoma can be determined by considering the following points:
- Adrenal adenoma manifests various imaging features on CT, MRI, and PET/CT 5
- The learning objectives of adrenal imaging for adenoma characterization include describing the imaging findings, comparing the sensitivities of different imaging modalities, and introducing differential diagnoses 5
- The established morphologic criteria for CT and MRI can be used to assess whether an adrenal mass is benign or malignant 6