Endocrine Abstracts

JOINT1780

Introduction: Phaeochromocytomas are increasingly diagnosed incidentally during cross-sectional imaging for other indications. Biochemical confirmation can be obtained via plasma free metanephrines or a 24-hour urine collection for normetanephrine and metanephrines. However, recent ESE guidelines suggest biochemical testing may not be necessary for patients with clear radiological features of an adrenal adenoma.

Methods: A retrospective analysis was conducted on the radiological and biochemical data of patients with incidentally discovered adrenal nodules reviewed at Cambridge University Hospital from 2019 to 2024. Only cases with formal radiological characterization of the adrenal nodule via unenhanced CT, dedicated CT adrenal imaging, or MRI were included. Data collected included age, gender, plasma metanephrines, laterality, tumour size, histology, genetics, and follow-up.

Results: A total of 631 patients were included, with 296 males (47%) and 335 females (53%). Of these, 507 (80.34%) had nodules with attenuation <10 Hounsfield units (HFU) or signal dropout on MRI. 61 patients (9.66%) had densities between 10 and 20 HFU, and 63 (10%) had densities >20 HFU. Most nodules (94.45%) were <4 cm in size, with 35 (5.55%) >4 cm. 521 nodules (82.56%) were unilateral and 110 (17.43%) bilateral. The mean age was 66 years (range 21–91). Two patients (0.4%) with radiologically characterized lipid-rich adenomas had abnormal plasma metanephrine results (<2 times the upper reference range), one of whom was on Venlafaxine. Both cases are pending further evaluation, with a low clinical suspicion for phaeochromocytoma. Among the 631 patients, 7 (1%) were diagnosed with phaeochromocytoma, all of which had nodules with densities >20 HFU on unenhanced CT scan adrenal glands. 4 were females and 3 males. It is important to mention that two (~28%) were reported as adenomas on washout studies but later confirmed as non-secretory pheochromocytomas. Histological analysis showed retained SDHB immunoreactivity in all cases. Genetic testing in five patients revealed an NF1 gene mutation in one with composite pheochromocytoma.

Conclusion: This study found a 1% prevalence of phaeochromocytoma in patients with incidentally discovered adrenal nodules. All confirmed cases had unenhanced nodules with densities >20 HFU. Histological analysis showed retained SDHB immunoreactivity, and genetic testing revealed an NF1 mutation in one patient. Two patients with lipid-rich adenomas had equivocal plasma metanephrine results, with further testing pending. Washout characteristics were unreliable in distinguishing benign from indeterminate lesions. These findings support the ESE guidelines, suggesting biochemical testing can be excluded in patients with radiologically characterized lipid-rich adrenal adenomas on unenhanced CT imaging of adrenal glands.