Endocrine Abstracts

Introduction: Pheochromocytomas are often diagnosed incidentally through cross-sectional imaging tests conducted for other reasons. Biochemical confirmation can be achieved through plasma free metanephrines and normetanephrines or a 24-hour urine collection for both normetanephrine and metanephrine. Recent ESE guidelines suggest that testing may not be necessary for patients with clear radiological features of adrenal adenomas.

Methods: We conducted a retrospective analysis of radiological and biochemical data for patients with incidentally discovered adrenal nodules at Cambridge University Hospital from 2019 to October 2024. Only cases with formal radiological characterization through unenhanced CT, dedicated CT adrenal, or MRI were included. Data collected included age, gender, plasma metanephrines, laterality, tumour size, and follow-up.

Results: This study included 631 patients: 296 (47%) males and 335 (53%) females. Among them, 507 (80.34%) had an attenuation of <10 HU or signal dropout on MRI. Sixty-one patients (9.66%) had nodules with densities between 10-20 HU, and 63 (10%) had densities >20 HU. Most nodules (596 or 94.45%) were <4 cm. The mean patient age was 66 years (range 21-91). Only 2 patients (0.4%) with lipid-rich adenomas showed abnormal plasma metanephrines. One individual is on Venlafaxine, and both cases await further assessment with low clinical suspicion for pheochromocytoma. From our data, only 7 patients (1.10%) had confirmed biochemical and histological diagnoses of pheochromocytoma, all with unenhanced densities >20 HU. This also suggests that 11.4% of patients with unenhanced densities greater than 20 HU had pheochromocytoma.

Conclusion: This single-centre study identified a ~1% prevalence of pheochromocytoma in patients with incidentally discovered adrenal nodules, all with unenhanced densities >20 HU. Two patients with lipid-rich adenomas had equivocal plasma metanephrine levels and await further testing. This analysis supports ESE guidelines to exclude biochemical testing for pheochromocytoma in patients with radiologically characterized lipid-rich adenomas.