[Case of 131I-meta-iodobenzylguanidine (MIBG) scintigraphy-negative and 2-[18F]-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET)-positive pheochromocytoma].

A 53-year-old man was admitted to Ehime University Hospital because of a left adrenal tumor, which was detected by a routine medical examination. Blood pressure was 124/74 mmHg and the pulse rate was 80/min and regular. Computed tomography showed the tumor consisting mainly of low-density areas and partly of heterogeneous density areas. Magnetic resonance imaging demonstrated that the tumor consisted mainly of low intensity areas, partly of heterogeneous intensity areas determined by T1-weighted images; T2-weighted images showed that the tumor consisted mainly of high intensity areas and partly of heterogeneous intensity areas. These images suggested that the left adrenal tumor was a pheochromocytoma. The concentrations of serum adrenaline and noradrenaline were slightly elevated (adrenaline 0.11 ng/mL (normal: < 0.1) and noradrenaline 1.11 ng/mL (normal 0.1 - 0.5)). Although 131I-meta-iodobenzylguanidine (MIBG) scintigraphy did not show an accumulation of the tracer, 2-[18F]-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) showed an increased accumulation of the tracer in the left adrenal tumor. These results were suggestive of the diagnosis of pheochromocytoma, and left adrenalectomy was performed by endoscopy. He was finally diagnosed with pheochromocytoma. The detection rate of pheochromocytoma by FDG-PET is not very high and has been reported to be about 70 %. However, FDG-PET may be useful for detecting local recurrence or distant metastasis, in patients with MIBG-negative pheochromocytoma.