December 2006

Provided by Dr. Ron Rosen of
PET/CT Imaging of San Jose

PATIENT HISTORY: This is a patient with a remote history of left breast cancer, presents with mediastinal and bihilar lymphadenopathy, as well as right lung nodules seen on recent CT.

PET/CT FINDINGS: A hypermetabolic focus is seen in the right lobe of the thyroid gland. Additionally, there are hypermetabolic AP window, precarinal, subcarinal, and bihilar lymph nodes. The right lung nodules measure only 6mm and 4mm and are not visualized on PET, possibly due to their small size.

AC=Attenuation Corrected PET images
NAC=Non-attenuation corrected PET images
FUSED=Fused PET and CT images

FOLLOW UP: Subsequent FNA of the right lobe of the thyroid gland revealed papillary thyroid cancer. Note: No pathology is yet available for the hypermetabolic mediastinal/bihilar lymph modes and their etiology remains uncertain.

CONCLUSION: PET/CT revealed unsuspected second primary malignancy in the right lobe of the thyroid gland.

FDG PET/CT and Unsuspected Second Primary Malignancies:
- Whole body FDG PET/CT detects unsuspected FDG-avid second primary malignancy in at least 1.2% of all patients undergoing PET/CT. Common sites of unsuspected second primary malignancy are lung, thyroid, colon, and breast. 1

- Incidental abnormal focal findings (incidentalomas) in the thyroid gland are seen in 1.2-4.0% of all patients who undergo FDG PET. 2-6 Of the thyroid incidentalomas who subsequently undergo FNA or surgery, 14-47% are found to be malignant. 2-6 In the vast majority of cases, the histopathology reveals papillary thyroid cancer. Occasionally, the histopathology shows non-Hodgkin's lymphoma, metastatic disease, or other types of thyroid cancer. 2-5

- Factors that correlate with malignancy are focal unilateral FDG uptake, and higher FDG uptake (higher standard uptake values-SUVs).2-5

- Focal thyroid incidentalomas should be viewed with suspicion. Further evaluation to exclude malignancy, usually primary thyroid cancer, may be warranted.

REFERENCES:
1. Ishimori T, Patel PV, Wahl RL. Detection of unexpected additional
primary malignancies with PET/CT. J Nucl Med. 2005;46:752-757.
2. Choi JY, Lee KS, Kim HJ, et al. Focal thyroid lesions incidentally
identified by integrated 18F-FDG PET/CT: clinical significance and
improved characterization. J Nucl Med. 2006;47:609-615.
3. Chen YK, Ding HJ, Chen KT, et al. Prevalence and risk of cancer of
focal thyroid incidentaloma identified by 18F-fluorodeoxyglucose
positron emission tomography for cancer screening in healthy subjects.
Anticancer Res. 2005;25:1421-1426.
4. Kang KW, Kim SK, Kang HS, et al. Prevalence and risk of cancer
of focal thyroid incidentaloma identified by 18F-
fluorodeoxyglucose positron emission tomography for metastasis
evaluation and cancer screening in healthy subjects. J Clin
Endocrinol Metab. 2003:88:4100-4104.
5. Cohen MS, Arslan N, Dehdashti F, et al. Risk of malignancy in
thyroid incidentalomas identified by fluorodeoxyglucose positron
emission tomography. Surgery. 2001;130: 941-946.