Japanese Journal of Clinical Oncology 34:280-281 (2004)
© 2004 Foundation for Promotion of Cancer Research
False-positive Finding on 18F-FDG PET after Chemotherapy for Primary Diffuse Large B-cell Lymphoma of the Thyroid: a Case Report
1 Division of General Surgery, Department of Surgical Sciences, University ‘La Sapienza’, Rome, Italy and 2 Department of Surgery, University of Oulu, Oulu, Finland
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONCASE REPORTDISCUSSIONREFERENCES |
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Primary non-Hodgkin lymphoma of the thyroid is an uncommon disease. It is a potentially aggressive disease and diffuse large B-cell lymphoma of the thyroid may result in 5 year survival rates <50%. Hence adequate follow-up and multimodality treatment for recurrent or persistent disease are required. Since 18F-FDG PET is considered the imaging method of choice for the detection and staging of lymphoma, this was used for restaging of a case of diffuse large B-cell lymphoma of the thyroid after chemotherapy and its diagnostic value is questioned in the present case report. In fact, PET showed a false-positive finding which led to unnecessary surgery.
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONCASE REPORTDISCUSSIONREFERENCES |
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Primary non-Hodgkin lymphoma of the thyroid is an uncommon disease, the incidence of which has been estimated to be 3.4% among other primary thyroid malignancies (1). Chemotherapy is considered the treatment of choice, but the potential aggressiveness of this disease requires adequate follow-up and multimodality treatment of recurrent or persistent disease. This is particularly true for diffuse large B-cell lymphoma of the thyroid, which has been reported to result in a 5 year survival rate of 44% (2). [18F]fluoro-2-deoxy-D-glucose positron emission tomography (18F-FDG PET) is considered the imaging method of choice for the detection and staging of lymphoma and has been used for restaging of a case of diffuse large B-cell lymphoma of the thyroid. Its diagnostic value is questioned, however, in the present case report.
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CASE REPORT |
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TOPABSTRACTINTRODUCTIONCASE REPORTDISCUSSIONREFERENCES |
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A 62-year-old woman presented with a thyroid mass. Four years before she had been diagnosed with thyroiditis and currently she was on levothyroxine treatment. A fine-needle biopsy of the mass suggested the diagnosis of subacute thyroiditis. Computed tomography (CT) of the neck and chest showed a multinodular goiter expanding into the mediastinum. A tumor involving the lobe of the thyroid was shown to dislocate both trachea and neck vessels. Furthermore, a lymph node about 1 cm in diameter was present at the left pulmonary hilum and a nodule 0.5 cm in diameter was present in the posterobasal segment of the left lung. Because the CT scan findings suggested a multinodular goiter, a thyroidectomy was planned. At surgery, a tumor of the left lobe of the thyroid was found to involve firmly the left cervical vessels. A biopsy was performed and examination of a frozen section specimen revealed an unspecified large cell tumor. Because of the extension of the mass and its likely aggressive nature, thyroidectomy was not performed. Histological examination showed a diffuse large B-cell lymphoma, CD20+ and CD79a+. The patient underwent chemotherapy with cyclophosphamide, doxorubicine, vincristine and prednisone. Four months later, a total body CT scan did not reveal any signs of recurrent or systemic disease. However, on ultrasound examination, persistence of a mass of 18 x 19 x 32 mm was detected in addition to other smaller nodules and an enlarged cervical lymph node. Cytological examination of a fine-needle biopsy obtained from the left lobe mass showed the presence of necrotic tissue. In order to rule out the persistence of the disease better, 18F-FDG PET was performed, which showed intense uptake of the marker at the level of the left lobe of the thyroid. A mild uptake of the marker was observed also at the level of the right paracardiac area and at the left pulmonary hilum (Fig. 1).
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Because of these findings, a total thyroidectomy was performed. The histological examination of the surgical specimen showed large areas of tissue necrosis in addition to monocytes, macrophages, giant cells and fibroblasts. Furthermore, signs of neovascularization and discrete cellular atypias were observed, but no signs of persistent disease were present. The postoperative course was uneventful. One year after thyroidectomy, neither symptoms nor signs on CT of the disease were present.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONCASE REPORTDISCUSSIONREFERENCES |
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PET represents a major advance in both staging and restaging of lymphoma. This is especially important as after treatment residual masses may call in question the possibility of residual disease. Indeed, it has been shown that in many cases lack of reduction of such tumoral masses after chemotherapy does not necessarily mean persistence of the disease (3). A recent analysis of the literature revealed that in the setting of restaging, 18F-FDG PET has a negative predictive value of 80–100%, but it has a variably low positive predictive value (19–60%) (4). This means that this method is associated with a significant number of false-positive findings, which necessarily have major therapeutic implications. In fact, in the case reported here, such a false-positive finding led to unnecessary total thyroidectomy. It is unknown why an increased uptake of FDG occurred in the thyroid mimicking disease, but it is possible that it was secondary to regeneration processes related to tumor necrosis or, more likely, to a local inflammatory process possibly related to the underlying chronic thyroiditis.
In conclusion, 18F-FDG PET for restaging of thyroid lymphoma can be associated with false-positive findings which may lead to unnecessary surgery. In case of positive findings on PET, a fine-needle aspiration of the residual mass is indicated.
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FOOTNOTES |
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+ For reprints and all correspondence: Fausto Biancari, Department of Surgery, Oulu University Hospital, P.O. Box 21, 90029 Oulu, Finland. E-mail: faustobiancari{at}yahoo.it
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REFERENCES |
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1 Mulla ZD, Margo CE. Primary malignancies of the thyroid: epidemiologic analysis of the Florida Cancer Data System Registry. Ann Epidemiol 2000;10:24–30.[CrossRef][Web of Science][Medline]
2 Thieblemont C, Mayer A, Dumontet C, Barbier Y, Callet-Bauchu E, Felman P, et al. Primary thyroid lymphoma is a heterogenous disease. J Clin Endocrinol Metab 2002;87:105–11.
3 Surbone A, Longo DL, DeVita VT Jr, Ihde DC, Duffey PL, Jaffe ES, et al. Residual abdominal masses in aggressive non-Hodgkin’s lymphoma after combination chemotherapy: significance and management. J Clin Oncol 1988;6:1832–7.[Abstract]
4 Reske SN. PET and restaging of malignant lymphoma including residual masses and relapse. Eur J Nucl Med Mol Imaging 2003;30(suppl. 1):S89–S96.
Received January 16, 2004; accepted March 1, 2004
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