Joint Program in Nuclear Medicine

PET CT Correlation: Incidentaloma in the Neck

Andrew F. Childs, MD PhD
David A. Israel, MD PhD

October 7, 2003

Presentation

A 47 year-old male with a history of Non-Hodgkin’s Lymphoma and bone marrow transplantation presented to Nuclear Medicine for a routine follow-up FDG-PET scan to rule out recurrence of disease.

Imaging Findings

A projection and slices (A: axial, B: coronal, and C: sagital) from an FDG-PET scan revealed a single focus of intense abnormal radiotracer uptake in the right lower neck at the cervicothoracic junction (show by arrows). Otherwise the study was unremarkable. The focus was considered suspicious for neoplasm and a follow up CT scan of the neck was requested for anatomic correlation.

Follow up Imaging

The CT study of the neck revealed no lymphadenopathy. There was however a small hypodense nodule in the right lower lobe of the thyroid (shown by arrow). The study was otherwise unremarkable.

Pathologic Correlation and Diagnosis

Under ultrasound guidance a fine needle aspirate of the thyroid nodule was obtained for pathologic correlation. The resulting tissue diagnosis was papillary carcinoma of the thyroid, follicular variant.

Diagnosis

Papillary carcinoma of the thyroid, follicular variant

Discussion

Incidental FDG avid lesions of the thyroid are occasionally found during PET studies and are often clinically significant. In a study by Van den Bruel et al.(1) fine needle aspirates were obtained from 8 patients referred to endocrinology for incidental FDG avid thyroid lesions. Based on the FNA results all eight patients had indications for surgery. Surgery was performed on seven of these patients with the tissue specimens revealing 2 medullary carcinomas, 3 follicular carcinomas and 2 follicular adenomas.

FDG-PET has reported sensitivities of 88%(2) and 96%(3) for the localizing of differentiated thyroid carcinomas. It is particularly useful, and is CMS approved(4), for the detection of follicular thyroid carcinoma following thyroidectomy and radiation therapy when the serum thyroglobulin is elevated (>10 ng/ml) and the I-131 whole body scan is negative(5,6). It may also be useful for the initial staging of thyroid cancers known to poorly concentrate radioactive iodine, and for the localization of medullary thyroid cancers in patients with elevated calcitonin levels when imaging fails to locate their metastatic lesions. Combined FDG-PET/CT is well suited to the localization of these disease sites(7). Positron emitting I-124 CT/PET, with its superior resolution as compared with I-131 SPECT, holds future promise for the localization of thyroid cancers that concentrate iodine(8).

References

1. Van den Bruel A, et. al. Clinical relevance of thyroid fluorodeoxyglucose-whole body positron emission tomography incidentaloma. J. Clin Endocrinol Metab 2002 April;87(4);1517-20.

2. Grunwald F, et al. Fluorine-18 fluorodeoxyglucose positron emission tomography in thyroid cancer: results of a multicentre study. Eur J Nucl Med 1999; 26:1545-1552.

3. Helal BO, et. al. Clinical impact of [18]F-FDG PET in thyroid carcinoma patients with elevated thyroglobulin levels and negative [131]I scanning results after therapy. J. Nucl Med 2001; 42: 1464-1469.

4. CMS National Coverage Determination for FDG PET for Thyroid Cancer. Administrative File CAG: #00095N. April 16, 2003.

5. Grunwald F, et. al., Fluorine-18 fluorodeoxyglucose positron emission tomography in the follow-up of differentiated thyroid cancer: Eur J Nucl Med. 1996 Mar;23(3):312-19.

6. Wang W. et al. FDG Positron emission tomography localizes residual thyroid patients with negative diagnostic [131]I whole body scans and elevated serum thyroglobulin. J Clin Endocrin & Metab, 1999; 84:7: 2291-2302.

7. Zimmer L, et. al. Combined positron emission tomography/computed tomography imaging of recurrent thyroid cancer. Otolaryngology-Head and Neck Surgery; 2003. 128:2: 178-184.

8. Freudenberg, MD, et al. Combined PET/CT with Iodine-124 in diagnosis of mediastinal micrometastases in thyroid carcinoma. The Internet Journal of Radiology 2002. Volume 2 Number 2.

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J. Anthony Parker, MD PhD, Tony_Parker@CareGroup.Harvard.edu