Malignant Pheochromocytoma Imaging with [124I]mIBG PET/MR

Abstract

Pheochromocytoma localized in the adrenal medulla (in 85%) or in the thoracic/abdominal sympathetic trunk (paraganglioma) has malignant potential in about 10% of cases. Metaiodobenzylguanidine (mIBG) can be labeled with 123-iodine (for scintigraphy), 131-iodine (basically for therapy), or 124-iodine [excellent positron emission tomography (PET) imaging and tumor dosimetry based on high spatial resolution] and has high sensitivity for the diagnosis of primary/metastatic pheochromocytoma (1–3). Thiscasereportsontheworldwidefirst [I]-mIBG-PET/ magnetic resonance imaging (MRI) performed with an integrated PET/MR (Biograph mMR; Siemens Healthcare, Erlangen, Germany) in a malignant pheochromocytoma. The addition of MRI to mIBG-PET is promising as it improves tumor delineation because of the high soft tissue contrast in MRI that is especially relevant in pretherapeutic dosimetry. Compared with conventional [I]mIBG scintigraphy, [I]mIBG-PET provides high-resolution images. A 24-yr-old woman suffering from progressive malignant pheochromocytoma (primary right adrenal) underwent dosimetry with [I]mIBG PET/computed tomography (CT) (50 MBq) for treatment planning before therapy with [I]mIBG. An additional whole-body PET/ MRI (48 h after [I]mIBG administration) was performed with the following examination parameters (entire acquisition time, 40 min): four bed positions (head to upper thigh); PET, 8-min list mode per bed position; MRI, DIXON (T1-weighted sequences in-/opposed phases) for acquiring the -map for attenuation correction, simultaneous with PET non-contrast-enhanced coronal T1, transversal fat-saturated T2, and diffusionweighted imaging non-simultaneous followed by coronal and axial fat-saturated T1 after administration of gadolinium-based contrast agent. The PET/MRI (Fig. 1A, PET maximum intensity projection (MIP); B, fused PET/MRI coronal T1; C, fused PET/CT coronal) revealed local tumor recurrence (right adrenal bed) and multiple metastases (liver, lymph nodes, abdominal muscles, peritoneal) with intense tracer uptake, hyperintense signal on T2, hypointense on nonen-