The role of MIBG scan in the diagnosis of pheochromocytoma.

Abstract

e15064 Background: Pheochromocytoma is an uncommon adrenal medulla tumor. Metaiodobenzylguanidine (MIBG) scintigraphy is the current gold standard functional imaging method for evaluating pheochromocytoma, due to its excellent 100% specificity, 80% sensitivity, and general availability. In addition to establishing an extension evaluation and monitoring medication efficacy, MIBG scintigraphy is essential to confirm the diagnosis of suspected pheochromocytoma, especially when there is a tumor-like adrenal mass whose etiology is to be determined and biopsy is contraindicated given the risk of catecholamine discharge with hypertensive flare and the risk of bleeding. Our aims are to determine the efficacy of scintigraphy in the diagnosis of pheochromocytoma by examining the epidemiological characteristic and uptake patterns of the disease. Methods: In a retrospective analysis from January 2010 to December 2020, we examined pheochromocytoma patients medical records who had been referred for MIBG scintigraphy to the regional western Algerian Nuclear Medicine department at the University Hospital Center of Tlemcen. Prior to a progressive intravenous injection of 40–80 MBq of l-MIBG, patients underwent preparation (discontinuation of interfering drugs with I-MIBG especially antihypertensive treatment, thyroid blocking, and hydration). Imaging acquisition was carried out 48 and 72 hours later. Results: Fifty patients with probable pheochromocytoma (sex ratio = 0,78; mean age = 43 [17-74] years) completed I-MIBG scintigraphy prior to adrenalectomy. The MIBG scan has a high specificity and positive predictive value (100%). It confirms the presence of pheochromocytoma in 21 cases (42%), even if the metanephrine is normal in a patient with a non-secreting pheochromocytoma. In 18 cases, the main pattern is a single, homogenous, and intense intra-abdominal uptake. For the three remaining patients, a voluminous and heterogeneous uptake with a photopenic center that was associated to a necrotic adrenal mass larger than 10 cm in size, seen on abdominal Computerized Tomography (CT). In this retrospective analysis, no cases of metastatic or multiple diseases were documented. The sensitivity and negative predictive value are 84% and 86%, respectively. In 29 patients (58%), the scan reveals no abnormalities in uptake. This is attributed, in part, to 30% false positive biology (sampling conditions of urinary and/or plasmatic metanephrines and/or normetanephrines), 20% false positive CT imaging (differential diagnosis of adrenal mass: benign or malignant adrenal nodule), and 8% false negative MIBG scintigraphy (subcentimetric, cystic and necrotic lesion). Conclusions: Due to its exceptional specificity, robust sensitivity, and whole-body staging, MIBG scintigraphy—along with biology and morphology imaging—is a crucial noninvasive diagnostic method for the management of pheochromocytoma prior to adrenalectomy.