Abstract
Pheochromocytomas may show atypical imaging findings leading to diagnostic pitfalls. We correlated the results of magnetic resonance imaging (MRI) with those of radionuclide studies in patients with pheochromocytomas. T2-weighted (-w), T1-w chemical-shift and T1-w dynamic contrast enhanced (DCE) MRI sequences were evaluated to assess tumor structure. 131Iodine metaiodobenzylguanidine (MIBG) scintigraphy, 18fluoro (F) deoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) or FDG PET/MRI were evaluated for direct comparison. Of a total of 80 adrenal lesions in 73 patients, 20 in 18 patients were pheochromocytomas. More than half (55%) of the pheochromocytomas (n = 11) had the typical increased signal intensity on T2-w and T1-w DCE, while the remaining (n = 9) lesions showed atypical findings; of these nine latter atypical lesions, seven (35%) were cystic (two totally, three predominantly and two partially) and two (10%) were hemorrhagic on MRI. In these atypical lesions, MIBG scintigraphy (n = 5), FDG PET/CT (n = 6) or FDG PET/MRI (n = 2) showed inhomogeneous tracer uptake in the residual viable tissue providing tumor characterization; however, one predominantly cystic pheochromocytoma showed false negative MIBG scan. Our preliminary results show that cystic degeneration may be frequent in pheochromocytoma being so marked that only a thin rim of viable cells may residue to disclose the true nature of the tumor. MRI findings together with those of correlative planar/hybrid radionuclide images are helpful to characterize these atypical pheochromocytomas. In particular, tumor accumulation of MIBG and/or FDG is able to classify these lesions as not simple cysts; in detail, the presence of partial MIBG uptake allows the diagnosis of pheochromocytomas, while the presence of partial FDG uptake generically reflects the presence of viable solid tissue of such cystic tumors.
Highlights
Pheochromocytomas are rare catecholamine-secreting neoplastic lesions arising from chromaffin cells of the adrenal medulla [1]
Patients with pheos were extrapolated and included in the final study population using the following criteria: (1) tumors proven by histopathology; (2) magnetic resonance imaging (MRI) study including T2-WI, T1-WI, chemical-shift (CS), T1-w dynamic contrast enhanced (DCE) sequences; (3) planar and/or hybrid radionuclide studies such as 131 I MIBG scintigraphy, 18 F FDG positron emission tomography/computed tomography (PET/computed tomography (CT)) and/or PET/MR); (4) clinical symptoms related to adrenal medullary hyperfunction as documented by plasma and urinary hormones levels such as catecholamines and/or their metabolites
Histopathology confirmation was available in 16 patients, while the remaining two patients refused surgical treatment; for these latter cases the results of radionuclide studies (MIBG) were considered to support and confirm tumor diagnosis
Summary
Pheochromocytomas (pheos) are rare catecholamine-secreting neoplastic lesions arising from chromaffin cells of the adrenal medulla [1] These tumors are clinically symptomatic for their increased catecholamine secretion and, imaging detection is required for treatment planning [2,3]. 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]
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