The Utility of Metaiodobenzylguanidine Single Photon Emission Computed Tomography/Computed Tomography (MIBG SPECT/CT) for the Diagnosis of Pheochromocytoma

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Abstract
The enhancement of metaiodobenzylguanidine single photon emission computed tomography (MIBG SPECT) imaging through the addition of CT images fused with SPECT data (coregistered MIBG SPECT/CT imaging) is new technology that allows direct correlation of anatomical and functional information. We hypothesized that MIBG SPECT/CT imaging would provide additional information and improve diagnostic confidence for the radiological localization of a pheochromocytoma, in particular for patients at high risk of multifocal or recurrent disease. A retrospective study of all patients investigated by MIBG SPECT/CT at our institution from 2006 to 2008 for a suspected pheochromocytoma was performed. Each case was compared with conventional radiological investigations to determine whether MIBG SPECT/CT was able to improve diagnostic confidence and provide additional diagnostic information compared with conventional imaging alone. Twenty-two patients had MIBG SPECT/CT imaging for a suspected pheochromocytoma. Fourteen patients had positive MIBG SPECT/CT imaging results correlating with imaging by CT or magnetic resonance imaging in all cases. In six cases, MIBG SPECT/CT provided additional information that altered the original radiological diagnosis. Five patients with a pheochromocytoma-associated germline mutation had multifocal disease excluded by MIBG SPECT/CT. Patients without a germline mutation that had positive biochemistry and a solitary lesion with conventional imaging had no diagnostic improvement with MIBG SPECT/CT imaging. MIBG SPECT/CT fusion imaging is a sensitive and specific radiological imaging tool for patients suspected to have pheochromocytoma. The particular strengths of MIBG SPECT/CT are detection of local recurrence, small extra-adrenal pheochromocytomas, multifocal tumors, or the presence of metastatic disease.