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| CASE REPORT |
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| Year : 2011 | Volume
: 26
| Issue : 4 | Page : 208-210 |
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False positive localisation of C-11 methionine in a colloid nodule
Sonia Mahajan1, Madhavi Tripathi1, Abhinav Jaimini1, Anant Dinesh2
1 Division of PET Imaging, Molecular Imaging and Research Centre, , New Delhi, India
2 Lok Nayak Jai Prakash Narayan Hospital, Maulana Azad Medical College, New Delhi, India
| Date of Web Publication | 1-Feb-2013 |
Correspondence Address:
Madhavi Tripathi
Room No: 201, Second floor, Division of Clinical PET, Molecular Imaging and Research Centre, Institute of Nuclear Medicine and Allied Sciences, New Delhi - 54
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/0972-3919.106719
 Abstract | | |
A 45-year-old female diagnosed with carcinoma of the left breast on histopathological examination underwent both 18 F-flourodeoxyglucose (FDG) and 11C-methionine (MET) positron emission tomography/computed tomography (PET/CT) as part of a protocol comparing the utility of these tracers for predicting a response to neoadjuvant chemotherapy in breast carcinoma. Abnormal FDG and MET accumulation was noted in the left breast primary, left axillary lymph nodes, and also in a well-defined nodule present in the left lobe of the thyroid gland. Keeping in mind the possibility of thyroid neoplasm/metastasis, the patient was referred for fine needle aspiration cytology (FNAC) from the thyroid nodule that revealed features of a simple colloid nodule. Focal thyroid lesions incidentally found on 18 F-FDG PET/CT have a high risk of thyroid malignancy. Non-specific accumulation of FDG in thyroid adenomas is also known. This case highlights a potential cause for false positive on C-11 MET PET/CT in colloid adenomas, which should be kept in mind while using this tracer for oncological indications. Keywords: Breast carcinoma, C-11 MET, colloid adenoma, F-18 flourodeoxyglucose
How to cite this article:
Mahajan S, Tripathi M, Jaimini A, Dinesh A. False positive localisation of C-11 methionine in a colloid nodule. Indian J Nucl Med 2011;26:208-10 |
How to cite this URL:
Mahajan S, Tripathi M, Jaimini A, Dinesh A. False positive localisation of C-11 methionine in a colloid nodule. Indian J Nucl Med [serial online] 2011 [cited 2021 May 12];26:208-10. Available from: https://www.ijnm.in/text.asp?2011/26/4/208/106719 |
| Introduction | |  |
A diagnosed case of carcinoma of the left breast planned for neoadjuvant chemotherapy underwent both 18F-Fluorodeoxyglucose (FDG) and 11C-methionine (MET) positron emission tomography/computed tomography (PET/CT). Both studies demonstrated intense focal tracer uptake in a nodule in the left lobe of thyroid. Cytopathology revealed it to be a colloid nodule. Thyroid lesions are frequently detected in patients undergoing FDG PET/CT. Some studies have reported that the incidence of thyroid incidentalomas with increased FDG uptake is 1.2-2.5% on PET examinations. [1],[2],[3],[4] The risk of malignancy in these studies ranged from 26.7-50%. With an increasing utility of amino acid tracers such as C-11 MET for oncological indications, non-oncological causes [5] of uptake of this tracer should be kept in mind to avoid misinterpretation of the study.
| Case Report | | |
A 45-year-old female presented with a left breast swelling since past 5 months. The swelling was single, painless, not fixed to the chest wall, and was associated with palpable left axillary lymphadeopathy. On histopathology, it was diagnosed as a case of infiltrating ductal cell carcinoma. As a part of protocol evaluating the utility of F-18 FDG and C-11 MET for prediction of response to neoadjuvant chemotherapy in locally advanced breast carcinoma the patient underwent the two studies on consecutive days. 222 MBq of FDG was injected intravenously and the patient was rested for 60 min followed by the PET/CT acquisition on a Discovery STE 16 camera (GE). 3D PET emission scan from head to thigh at 2 min per incremental bed position was acquired. C-11 MET PET/CT was done the next day 30 min after injecting 555 MBq of tracer followed by a two bed 3D PET acquisition for 10 min per bed position, with the axilla and chest in the acquisition field. Images were reconstructed using 3D VUE algorithm and viewed on a Xeleris workstation (GE) using the volumetrix protocol. On evaluation of the maximum intensity projection (MIP) image, abnormal FDG [Figure 1]a and MET [Figure 2]a accumulation was noted in the left breast and left axillary region and also in the left side of the neck. The transaxial fused PET/CT images [Figures 1]b and [Figure 2]b localised this uptake to a well-defined solitary hypodense nodule in the left lobe of thyroid. On retrospective examination, a nodule, soft to firm in consistency and moving with deglutition was palpable in the left lobe of thyroid. The patient was referred for a FNAC prior to starting chemotherapy, which revealed features of a simple colloid nodule. Neoadjuvant chemotherapy with cyclophosphamide, adriamycin, and 5-flurouracil was started the next day.
| Discussion | | |
Thyroid nodules with abnormal increased tracer accumulation may be incidentally discovered on the FDG PET/CT study for other oncological indications. Increased FDG uptake can be observed in thyroid carcinoma and metastatic nodules due to augmented expression of glucose transport proteins such as GLUT-1, enhanced glycolysis, and increased cellular proliferation. [6],[7],[8] However, FDG also accumulates non-specifically in infectious, inflammatory diseases, or simply benign thyroid nodules secondary to lymphoid tissue activation, increased metabolic activity, and rapid iodine turnover. [9],[10] The lack of specificity of FDG has prompted the use of radiolabeled amino acids such as C-11 methionine.
MET follows metabolic pathways of methionine and is a potential tracer to image altered amino acid metabolism in cancer. Methionine is needed for protein synthesis and as a precursor of S-adenosylmethionine, which is the most important biological methyl group donor in several biochemical reactions (e.g., methylation of DNA) in vivo. [11],[12] However, recent studies have suggested that tissue accumulation of methionine is primarily related to active transport of amino acids rather than to protein synthesis rate. [13] The increased utilization of methionine can be measured by PET using radiolabeled MET as the tracer. Uptake of MET in tumor tissue is rapid, and it has been evaluated for use in brain tumors, breast cancer, and pelvic malignancies. The recent advent of MET imaging in oncology has brought its own specific pitfalls and artefacts. [5] Knowledge of these potentially false positive causes of uptake is crucial to avoid misinterpretation of images. The possibility of MET accumulation in benign thyroid pathologies such as a colloid nodule has not been reported so far, but should be kept in mind while reporting the MET study in oncology and confirmatory cytopathology is recommended.
| References | | |
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[Figure 1], [Figure 2]
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