Introduction/Background: Adrenal incidentaloma is defined as an asymptomatic adrenal mass greater than 1 cm, discovered during imaging performed for another purpose1. The main goal when discovering such a tumor is to rule out a hormonally active lesion or a malignant condition. Radiological characteristics on non-contrast CT or MRI can help to determine if a lesion is benign. If the lesion nature remains indeterminate after these exams, it is recommended to perform a FDG-PET/CT1. Here, we report a unique case of benign adrenal incidentaloma with abnormal radiological features and hypermetabolic pattern.
Case summary: A 53-year-old woman was referred to our Department of endocrinology in May 2019 for a bilateral adrenal incidentaloma. The lesions were discovered during an MRI of the kidney. The radiologist described a left adrenal lesion of 16x15.5mm, without enhancement on T2 weighted images. There was no loss of signal intensity on out-phase imaging and the contrast media washout was delayed. The right adrenal lesion of 10x17mm had a characteristic pattern of adrenal adenoma. The left adrenal lesion was not present on a CT scanner performed in 2015, while the right lesion was stable. Clinical examination revealed weight loss and two centimetric lymphadenopathies : one in the right supra-clavicular area and the other in the left posterior cervical area. Considering the above and that the patient was an active smoker, an additional work-up was carried out. The aldosterone-to-renin ratio was a bit high due to beta-blockers, but aldosterone level was normal. Urinary metanephrines and normetanephrines, morning serum cortisol, 1-mg overnight dexamethasone suppression test, 17-hydroxyprogesterone, and DHEAS were normal. Abdominal non-contrast CT showed a growing left adrenal lesion (20x15mm) of 43 Hounsfield unit. Due to the rapid progression of the lesion and the atypical radiological features, a FDG-PET/CT was planned. The exam showed a hypermetabolic lesion (SUV max 7.2; adrenal to liver SUV ratio 1.95), without other suspect lesion. A laparoscopic left adrenalectomy was performed. Histopathologic analysis revealed an intra-adrenal lymphoid organ of 15 mm, localized in the medulla. There were numerous big germinal centers and no cellular atypia. Massons trichrome stain suggested the presence of a capsule. On immunohistochemistry, B cells (CD20+/CD3-) and T cells (CD20-/CD3+) organization was normal, with a low CD68 staining. The surrounding adrenal tissue showed good corticomedullary differentiation, without any specific lesions. Early post-operative follow-up was unremarkable and the patient did not develop any problems over the following 2 years.
Discussion/Conclusion: Over 80% of the etiologies of resected adrenal incidentalomas are adrenocortical adenoma, adrenocortical carcinoma, pheochromocytoma and myelolipoma. Cystic lesions, ganglioneuroma and metastases account for less than 15% of the total, and the remainder are rare entities1,2. Elevated adrenal to liver SUV ratio and SUV max measures on FDG-PET/CT are useful tools to distinguish a benign from a malignant adrenal tumor, with a sensitivity ranging from 85% to 100%1. Therefore, the hypermetabolic status of the incidentaloma raised the question of a lymphoproliferative disorder. However, this hypothesis was quickly ruled out by the absence of cellular or architectural atypia and normal immunohistochemistry. The only publication reporting a benign intra-adrenal lymphoid structure described an isolated lymphoid follicle, also located in the medulla3. We report a bigger and more organized lymphoid structure which mimics a lymphoid organ. However, we were unable to classify it as secondary or tertiary lymphoid organ. Indeed, the adrenal medulla does not usually contain lymph nodes (secondary lymphoid organ). Furthermore, we did not find surrounding tumor or chronic inflammation, characterizing tertiary lymphoid organs4. In conclusion, we describe a unique case of an adrenal incidentaloma suspected of malignancy, which turned out to be a benign ectopic lymphoid organ.
References: 1. Fassnacht M, Tsagarakis S, Terzolo M, et al. European Society of Endocrinology Clinical Practice Guidelines on the management of adrenal incidentalomas, in collaboration with the European Network for the Study of Adrenal Tumors. Eur J Endocrinol. Published online June 15, 2023:G1-G34. doi:10.1530/EJE-16-0467.2. Mantero F, Terzolo M, Arnaldi G, et al. A survey on adrenal incidentaloma in Italy. Study Group on Adrenal Tumors of the Italian Society of Endocrinology. J Clin Endocrinol Metab. 2000;85(2):637-644. doi:10.1210/jcem.85.2.6372.3. Nava VE, Torres-Cabala C. Novel Intra-Adrenal Secondary Lymphoid Follicle Formation. Endocr Pathol. 2013;24(4):248-249. doi:10.1007/s12022-013-9261-z.4. Ruddle NH. Lymphatic vessels and tertiary lymphoid organs. J Clin Invest. 2014;124(3):953-959. doi:10.1172/JCI71611.