_Applied sciences_  
_Article_  
**Characterization of Atypical Pheochromocytomas with**  
**Correlative MRI and Planar/Hybrid Radionuclide Imaging:**  
**A Preliminary Study**  
**[PERSON] 1,*, [PERSON] 1, [PERSON] 1, [PERSON] 1, [PERSON] 1, [PERSON] 2,**  
**[PERSON] 2, [PERSON] 1, [PERSON] 3, [PERSON] 4, [PERSON] 4, [PERSON] 4 and [PERSON] 1\({}^{\copyright}\)**  
* Department of Advanced Biomedical Sciences, University of Naples \"Federico II\", 80131 Naples, Italy; [EMAIL_ADDRESS] (L.A.); [PERSON]S] (V.R.); [EMAIL_ADDRESS] (C.M.); michele.kalianfounina.it (M.K.); eilaguadagno@[EMAIL_ADDRESS] (E.G.); [EMAIL_ADDRESS] (S.M.)
* Department of Clinical Medicine and Surgery, Division of Endocrinology, University of Naples \"Federico II\", 80131 Naples, Italy; [EMAIL_ADDRESS] (C.S.); [EMAIL_ADDRESS] (R.M.)
* Department of General and Mini-Invasive Surgery, University of Naples \"Federico II\", 80131 Naples, Italy; [EMAIL_ADDRESS]
* IRCCS SDN, 80143 Naples, Italy; [EMAIL_ADDRESS] (L.B.); [EMAIL_ADDRESS] (E.N.); macroslavator2.segreg  
such patients. Usually, on MRI pheos appear as solid round masses with homogeneous increased signal intensity on T2-weighted (-WI) and low signal intensity on T1-WI images with avid enhancing and poor wash-out after intravenous contrast medium administration on T1-WI dynamic contrast enhanced (DCE) sequence [2]. Moreover, on radionuclide imaging these tumors show increased focal tracer uptake using radiolabeled agents such as metaiodobenzylguanidine (MIBG), dihydroxyphenylalanine (DOPA), fluorodeoxyglucose (FDG) and somatostatin analogs [4; 5; 6; 7; 8; 9; 10]; in particular, these radiopharmaceuticals target specific functional and molecular tumor pathways reflecting catecholamine synthesis, glucose metabolism and somatostatin receptors (SR) expression, respectively. However, pheos may show atypical lesion characteristics when undergoing different degrees of tissue degeneration such as necrosis, hemorrhage, calcification, cystic or intracellular lipid changes, making their clinical and imaging behaviors unpredictable as well as mimicking other adrenal tumors [2; 8; 9; 10; 11; 12; 13; 14]. Of note, [PERSON] et al. [11] reported increased MRI signal intensity heterogeneity correlating pathologically with high amounts of haemorrhage, necrosis and fibrosis; of note, cystic degeneration may be so marked that only a thin rim of viable cells may remain to disclose the true nature of lesion [12]. [PERSON] et al. [15] described several atypical patterns of pheos consisting of cystic change, hemorrhage, intense contrast enhancement, calcifications and intracellular lipid component. Similarly, MIBG scintigraphy has been described to be useful in atypical pheo showing increased tracer uptake only in the solid viable peripheral portion of tumors [15; 16; 17]. For these reasons, the discovery of these atypical pheos is not easy in clinical practice, often resulting in delayed diagnostic and therapeutic management with clinical consequences because of excessive catecholamine production [1; 18]. To further complicate the clinical scenario, hereditary pheos may show false negative radionuclide MIBG images, getting the diagnosis even more difficult [3].  
The aim of this retrospective study was to assess the correlative images using MRI and radionuclide techniques in atypical pheos in order to describe imaging features of such tumors which may reflect morpho-functional lesion features and thus may help in tumor diagnosis and characterization.