Ann Thorac Surg 2006;81:1132-1134
© 2006 The Society of Thoracic Surgeons
Case report
Positive Imaging of Thymoma by 11C-Acetate Positron Emission Tomography
Takashi Ohtsuka, MD
a
,
*
,
Hiroaki Nomori, MD, PhD
a
,
Kenichi Watanabe, MD
a
,
Tsuguo Naruke, MD, PhD
a
,
Keiichi Suemasu, MD, PhD
a
,
Noboru Kosaka, MD, PhD
b
,
Kimiichi Uno, MD, PhD
b
a Department of Thoracic Surgery and Saiseikai Central Hospital, Tokyo, Japan
b Nishidai Clinic, Tokyo, Japan
Accepted for publication January 5, 2005.
* Address correspondence to Dr Ohtsuka, Department of Thoracic Surgery, Saiseikai Central Hospital, 1-4-17 Mita, Minato-ku, Tokyo, 108-0073 Japan (Email: t-oh{at}remus.dti.ne.jp).
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Abstract
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Several studies have shown that fluorine-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) is not useful for the diagnosis of thymoma. We describe 3 patients with thymoma who underwent both FDG-PET and carbon-11 (11C) acetate (AC)-PET. Although all three thymomas were successfully imaged by AC-PET, one of the thymomas was not imaged by FDG-PET. These results suggest that AC-PET may have a potentially important role in the diagnosis of thymoma. This is the first report of the use of AC-PET for diagnostic imaging of thymoma.
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Introduction
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Recently, carbon-11 (11C) acetate (AC)-PET has been reported to be of clinical value for the diagnosis of cancers that are not imaged by fluorine-18 fluorodeoxyglucose (FDG)-PET, such as prostate cancer and hepatocellular carcinoma [1, 2]. Here we describe three cases of thymoma that were imaged by AC-PET.
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Case Reports
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Between June and September 2004, 3 patients with thymomas underwent whole-body FDG-PET and AC-PET. The characteristics of the 3 patients are summarized in Table 1. After obtaining the patients' informed consent, AC-PET was performed before FDG-PET on the same day. The dosage of 11C acetate administered was 125 µCi/kg (4.6 MBq/kg). Positron emission tomographic imaging was performed approximately 10 minutes after administration of AC using a POSICAM.HZL mPOWER (Positron Co, Houston, Texas). The emission scans were initially obtained in two-dimensional mode for 4 minutes per bed position and taken from the top of the skull to the thighs. Approximately 30 minutes after AC-positron emission tomographic imaging, fluorine-18 FDG was administered (ie, more than 120 minutes after administration of the acetate). The dosage of FDG was 125 µCi/kg (4.6 MBq/kg) for nondiabetic patients and 150 µCi/kg (5.6 MBq/kg) for diabetic patients, as we reported previously [3]. The FDG-PET scans were performed approximately 45 minutes after administration of FDG. The images were reconstructed using the emission scans and the preinjection transmission scans in a 128 x 128 matrix by ordered subset expectation maximization corresponding to a pixel size of 4 x 4 mm, with a section spacing of 2.56 mm.
Patient 1
Chest computed tomography (CT) showed a tumor located in the anterior mediastinum, measured 3 x 3 cm (Fig 1A). An AC-positron emission tomographic scan showed accumulation at the tumor site with a standardized uptake value (SUV) of 3.5 (Fig 1B), although FDG-PET showed no accumulation with an SUV of 1.0 (Fig 1C). Thymothymectomy was performed, and histopathologic examination showed a thymoma (World Health Organization [WHO] type AB), which had invaded the capsule.
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Fig 1. Acetate-positron emission tomography (AC-PET), fluorodeoxyglucose-positron emission tomography (FDG-PET), and computed tomography (CT) in 3 thymoma patients. All 3 thymomas were successfully imaged by AC-PET (A, D, G). By FDG-PET, 2 patients were imaged (E, H), but one was not imaged (B). Chest CT showed anterior mediastinal tumors (C, F, I).
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Patient 2
Chest CT showed a tumor measuring 4 x 4 cm located in the anterior mediastinum (Fig 1D). An 11C-acetate PET showed accumulation at the tumor site with an SUV of 2.7. (Fig 1E), and FDG-PET also showed accumulation at the tumor site with an SUV of 5.9 (Fig 1F). Thymothymectomy was performed and histopathologic examination showed a thymoma (WHO type B1) that had invaded the capsule.
Patient 3
Chest CT showed a tumor located in the anterior mediastinum, measuring 7 x 7 cm (Fig 1G). An AC-PET showed strong accumulation at the tumor site with an SUV of 5.9 (Fig 1H), although FDG-PET showed accumulation with an SUV of 3.1 (Fig 1I). Thymothymectomy was performed, and histopathologic examination showed a thymoma (WHO type AB) that had invaded the capsule.
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Comment
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Thymic tumors are the most common tumors arising in the anterior mediastinum. Clinically the diagnosis of thymic tumors is performed mainly by morphologic examinations, such as CT and magnetic resonance imaging (MRI). Although both CT and MRI have also been reported to be useful for the differential diagnosis of thymic tumors [4], such diagnosis still remains difficult in some cases. FDG-PET has been reported to show high uptake of FDG in thymic cancer, but not in thymoma [5], probably due to its slow growth [6], and low glucose uptake. In the present report we have described three patients of thymomas that were positively imaged by AC-PET. Acetate has been used as a positron-emitting tracer for measurement of oxidative metabolism in the myocardium. The mechanism by which acetate shows high accumulation in tumor cells is still unknown, although it is considered to differ from that of myocardial uptake [7, 8]. Several studies have shown that 11C acetate has higher sensitivity for the detection of prostate cancer [2] and higher sensitivity and specificity for the diagnosis of well-differentiated hepatocellular carcinoma than FDG-PET [1]. Higashi and colleagues [8] described a case of bronchioloalveolar carcinoma in which FDG-PET showed lower uptake than the AC-PET did, suggesting that acetate might accumulate in slow-growing tumors.
We have demonstrated that three patients of thymoma were positively imaged by AC-PET despite showing different results with FDG-PET. Our findings suggest that AC-PET may have a potentially important role in the diagnosis of thymoma, as is the case for other slow-growing tumors such as prostate cancer and bronchioloalveolar carcinoma.
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References
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1271 - 1274.
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Abstract
Introduction
