Case Author(s): Edward Pinkus,M.D. and Jerold Wallis,M.D. , 3/7/02 . Rating: #D3, #Q4

Diagnosis: Poorly differentiated papillary thyroid cancer.

Brief history:

Status post thyroidectomy for poorly differentiated thyroid cancer.

Images:

Coronal whole body fdg-pet images.

View main image(pt) in a separate image viewer

View second image(tr). Whole body images 115 hours after administration of 200 mCi of I-131.

View third image(ct). CT of the chest

View fourth image(ct). CT of the neck

Full history/Diagnosis is available below

Diagnosis: Poorly differentiated papillary thyroid cancer.

Full history:

56 year old man with poorly differentiated papillary thyroid cancer. Status post thyroidectomy, 200 mci I-131 ablation. Whole body I-131 images show a large amount of uptake in the thyroid bed, but with fewer lesions in the lung than evident on CT.

Radiopharmaceutical:

14.5 mCi F-18 FDG.

Findings:

FDG-PET: There are several foci of intensely increased FDG uptake in the right neck, posterior thyroid bed, left axilla, right paratracheal, multiple nodules in the lungs, and right adrenal. Some of the nodules correlate with uptake on the I-131 post ablation scan. There is also mild uptake in the right glenoid, left sacrum, the L-3 spinous process, left L-3 transverse process without CT-correlate.

I-131 scan: Intense uptake in the region of thyroid gland. There multiple foci of uptake in the lung bases (though some could be in adjacent transverse colon), however, after comparison with CT, not all of the masses evident on CT demonstrate uptake on the I-131 images.

CT-pre-thyroidectomy: Thyroid mass with invasion into the tracheal membrane, with innumerable pulmonary masses.

Discussion:

Well differentiated papillary and follicular thyroid cancer is generally well-visualized on I-131 imaging, but may be poorly seen on FDG imaging due to the relatively low metabolic activity of the lesions. In contrast, poorly differentiated thyroid carcinoma is seen well on FDG imaging, but less well visualized on I-131 imaging. PET imaging may be useful if the tumor burden is suspected to be greater than that seen on I-131 scans.

Selected patients with thyroid cancer can benefit from the use of PET imaging with FDG or with I-124. The PET scan impacts on management by providing (1) more accurate information about staging of patients in terms of extent of tumor for better treatment planning, especially in patients who do not concentration radioactive I-131; (2) the relationship of tumor involvement to vital structures, especially in the neck and central nervous system; and (3) prognostic information (an SUV > 10 and extensive PET + disease connotes a poor prognosis in advanced patients). In the occasional patient, surgically respectable disease has been identified on PET with the result that the patient has been rendered no evident disease with treatment. PET has also been used in the follow-up of patients who have been treated for thyroid cancer, to assess response. PET may also be useful for lesion specific dosimetry, with I-124. The combination of PET and CT in the same gantry facilitates localization of thyroid cancer PET scan abnormalities in relationship to critical organs and structures.

Semin Roentgenol 2002 Apr;37(2):169-74 Positron emission tomography in thyroid cancer management. Larson SM, Robbins R. Department of Radiology, Nuclear Medicine Service, Laurent and Alberta Gershel PET Center, New York, NY, USA.

ACR Codes and Keywords:

References and General Discussion of PET Tumor Imaging Studies (Anatomic field:Face, Mastoids, and Neck, Category:Neoplasm, Neoplastic-like condition)

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Case number: pt072

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