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Year : 2020  |  Volume : 35  |  Issue : 2  |  Page : 185-186  

Low-grade thymoma with osseous and pulmonary metastases: Role of18F-fluorodeoxyglucose positron emission tomography–computed tomography in initial staging


Department of Nuclear Medicine, All India Institute of Medical Sciences, New Delhi, India

Date of Submission01-Sep-2019
Date of Acceptance18-Sep-2019
Date of Web Publication12-Mar-2020

Correspondence Address:
Dr. Rakesh Kumar
Department of Nuclear Medicine, Division of Diagnostic Nuclear Medicine, All India Institute of Medical Sciences, New Delhi - 110 029
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijnm.IJNM_160_19

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   Abstract 


Thymomas are rare anterior mediastinal tumors that originate in the epithelial cells of the thymus and have a rare propensity to metastasize to extrathoracic locations unless it is a histologic high-grade neoplasm (type B and above). We describe a case of 50-year-old woman diagnosed with type AB thymoma and the role of18F-fluorodeoxyglucose positron emission tomography–computed tomography in accurate delineation of extrathoracic metastases during initial staging.

Keywords: Metastases, osseous, positron emission tomography–computed tomography, pulmonary, thymoma


How to cite this article:
Tripathy S, Arun Raj ST, Subudhi K, Kaushik P, Kumar R. Low-grade thymoma with osseous and pulmonary metastases: Role of18F-fluorodeoxyglucose positron emission tomography–computed tomography in initial staging. Indian J Nucl Med 2020;35:185-6

How to cite this URL:
Tripathy S, Arun Raj ST, Subudhi K, Kaushik P, Kumar R. Low-grade thymoma with osseous and pulmonary metastases: Role of18F-fluorodeoxyglucose positron emission tomography–computed tomography in initial staging. Indian J Nucl Med [serial online] 2020 [cited 2020 Jul 10];35:185-6. Available from: http://www.ijnm.in/text.asp?2020/35/2/185/280441



A 50-year-old woman with chief complaints of cough and dyspnea for 6 months underwent contrast-enhanced computed tomography (CT) chest which revealed a large anterior mediastinal mass with no evidence of mediastinal vessels invasion. Biopsy from the mass showed AB-type thymoma with tumor cells immunopositive for pan-cytokeratin and TdT while negative for calcitonin. Then, the patient was subjected to18 F-fluorodeoxyglucose positron emission tomography–CT (18 F FDG PET-CT) scan [Figure 1] to rule out any distant metastases. PET-CT scan findings revealed heterogeneous area of FDG uptake in the thoracic region and two discrete foci of radiotracer uptake in the right proximal thigh region [Figure 1]a. Fused coronal PET-CT image showed heterogeneous FDG uptake in the anterior mediastinal mass that measured ~7.6 transverse (TR) cm × 5.6 Antero-posterior (AP) cm × 10 cranio-caudal (CC) cm [Figure 1]b. Few FDG avid nodules in the bilateral lung fields were seen in fused axial PET-CT images [Figure 1]c and [Figure 1]d, nodule in the left lung lower lobe by solid white arrow and nodule in the right lung lower lobe by solid white arrow, respectively]. Also seen were focal areas of increased FDG uptake in the right pelvic region (solid black arrows) on maximum intensity projection image which were localized to lytic lesions in the lower lip of right acetabulum and right ischium on fused transaxial18 F FDG PET-CT images [Figure 1]e, solid white arrow].
Figure 1: (a) Maximum intensity projection image of fluorodeoxyglucose positron emission tomography–computed tomography showing heterogeneous area of fluorodeoxyglucose uptake in the thorax and two other discrete foci of fluorodeoxyglucose uptake in the right proximal thigh region (solid black arrows). (b) Fused coronal positron emission tomography–computed tomography image showing enlarged anterior mediastinal mass with heterogeneous fluorodeoxyglucose uptake. (c and d) Fused axial positron emission tomography–computed tomography image showing two discrete nodules in both the lungs (solid white arrows). (e) Fused axial positron emission tomography–computed tomography image showing fluorodeoxyglucose avid lytic lesions in the right ischium (solid white arrow)

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Thymomas are rare epithelial neoplasms (0.2%–1.5% of all malignancies) and mostly occur in the anterosuperior mediastinum. They are classified on histologic basis as types A, AB, B1, B2, B3, and C (thymic carcinoma).[1] Most of the thymomas invading the neighboring organs or presenting with distant metastasis are of histologic types B and C.[2],[3],[4] The most common extrathoracic metastatic site of thymomas remain lung followed by liver, lymph nodes, and bones.[5],[6],[7]18 F FDG PET-CT can be helpful in predicting the histology and evaluating the exact extent of the disease for the initial staging of tumor.[8] Although the incidence of metastases is seen higher in cases of thymic carcinomas and thymic neuroendocrine carcinomas, this case shows that, although uncommon, low-grade thymomas can also manifest with extrathoracic metastases. The authors advocate the routine use of18 F FDG PET-CT high-grade as well as low-grade thymic epithelial neoplasms for initial staging purposes and accurately rule out distant metastases if any before proper therapeutic interventions are commenced.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
   References Top

1.
Marx A, Chan JK, Coindre JM, Detterbeck F, Girard N, Harris NL, et al. The 2015 world health organization classification of tumors of the thymus: Continuity and changes. J Thorac Oncol 2015;10:1383-95.  Back to cited text no. 1
    
2.
Lococo F, Cafarotti S, Cesario A, Dall'Armi V, Cusumano G, Lauriola L, et al. Prognostic grading after complete resection for thymic malignancies. Eur Rev Med Pharmacol Sci 2015;19:2882-91.  Back to cited text no. 2
    
3.
Margaritora S, Cesario A, Cusumano G, Lococo F, Porziella V, Meacci E, et al. Single-centre 40-year results of redo operation for recurrent thymomas. Eur J Cardiothorac Surg 2011;40:894-900.  Back to cited text no. 3
    
4.
Lewis JE, Wick MR, Scheithauer BW, Bernatz PE, Taylor WF. Thymoma. A clinicopathologic review. Cancer 1987;60:2727-43.  Back to cited text no. 4
    
5.
Masaoka A, Monden Y, Nakahara K, Tanioka T. Follow-up study of thymomas with special reference to their clinical stages. Cancer 1981;48:2485-92.  Back to cited text no. 5
    
6.
Vladislav T, Jain RK, Alvarez R, Mehta RJ, Gökmen-Polar Y, Kesler KA, et al. Extrathoracic metastases of thymic origin: A review of 35 cases. Mod Pathol 2012;25:370-7.  Back to cited text no. 6
    
7.
Hoshino S, Furukawa M, Aragane K, Horimoto M, Suzuki K, Shiono H, et al. Successful multimodal treatment in a patient with thymoma accompanied by hepatic metastasis. J Thorac Oncol 2008;3:98-100.  Back to cited text no. 7
    
8.
Otsuka H. The utility of FDG-PET in the diagnosis of thymic epithelial tumors. J Med Invest 2012;59:225-34.  Back to cited text no. 8
    


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