Adrenal incidentaloma: imaging characterisation

What is an adrenal incidentaloma?

An adrenal incidentaloma is a mass of the adrenal gland discovered incidentally during an imaging examination (CT or MRI) performed for a reason unrelated to the adrenal gland. Its frequency increases with age and with the widespread use of CT in the work-up of many abdominal conditions: it is estimated at about 5% of abdominal CT scans performed in adults.

The vast majority of these findings correspond to a benign adrenal adenoma, a non-secreting tumour with no potential for progression. Adrenocortical carcinoma is a rare but aggressive malignant tumour, whose early diagnosis strongly determines the prognosis - hence the importance of rigorous imaging characterisation before any decision on surveillance or surgical management.

The role of imaging: distinguishing adenoma from adrenocortical carcinoma

Most adrenal adenomas are rich in intracellular fat, which allows simple and reliable characterisation on unenhanced CT by measuring the spontaneous density of the lesion (in Hounsfield units). A mass with low spontaneous density is considered a typical adenoma, with no need for further investigation.

The diagnostic difficulty concerns lipid-poor adenomas, whose CT appearance resembles that of a malignant lesion. In this situation, multiparametric MRI is indicated to refine the characterisation, combining:

• In-phase and opposed-phase sequences (chemical-shift imaging): looking for a signal drop reflecting the presence of intracellular fat, even in small amounts.
• Diffusion sequences: measurement of the apparent diffusion coefficient (ADC), generally lower in malignant lesions because of denser tumour cellularity.

Staging and the international ENSAT network

When the diagnosis of adrenocortical carcinoma is confirmed or strongly suspected, staging relies on the classification of the European Network for the Study of Adrenal Tumors (ENSAT), which is the reference for the prognostic stratification of this rare tumour. Recent research shows that a score combining CT morphological criteria (shape elongation, maximum tumour diameter) with the ENSAT stage further refines prognostic stratification compared with the ENSAT stage alone.

This approach is part of a broader movement towards radiomics and artificial intelligence applied to adrenal imaging, aiming to extract quantitative biomarkers from images to improve the characterisation and prognosis of adrenal tumours, beyond visual reading alone.

Patient pathway

• Unenhanced CT: first step when an adrenal mass is discovered incidentally, for an initial characterisation based on spontaneous density.
• Biochemical hormonal work-up: systematically associated, looking for hormonal secretion (cortisol, aldosterone, metanephrines) that may guide management regardless of whether the lesion is benign or malignant.
• Multiparametric MRI: in the case of a lipid-poor adenoma or inconclusive CT characterisation.
• Image-guided percutaneous biopsy: reserved for selected situations, in consultation with the endocrinologist, in the absence of a context suggestive of phaeochromocytoma (a classic contraindication to biopsy).
• Multidisciplinary meeting (endocrinology, endocrine surgery, radiology): required for any indeterminate or suspicious adrenal mass, to decide between surveillance and surgical resection.

Frequently asked questions