Objective : The advent of cross sectional imaging techniques for diagnosis and management of disease has led to an increase in the number of incidental findings. Thyroid nodules are often incidentally found on imaging studies with an estimated 25% incidence on neck CT scan. We present the case of a thyroid nodule that was discovered on routine oncologic surveillance of a patient with a known history of metastatic renal cell carcinoma.
Methods : n/a
An 83-year-old man presented for evaluation for non-toxic multinodular goiter. His past medical history was significant for renal clear cell carcinoma that was initially diagnosed 5 years prior in the setting of a pathologic right femur fracture requiring mass excision, fixation of the right femur, right radical nephrectomy, and XRT. During routine cancer surveillance, a PET-CT demonstrated a FDG-avid right-sided thyroid nodule with a standard uptake value (SUV) of 4.58. Thyroid ultrasound revealed a 2.2 cm hypoechoic nodule in the right middle lobe with faint microcalcifications, corresponding to the previously noted area of PET-avidity. The patient denied any dysphagia, odynophagia, history of radiation to the neck, or family history of thyroid cancer. Thyroid function tests were normal. Thyroid biopsy showed cohesive groups of cells with large nuclei, irregular nuclear contours, granular chromatin with finely vacuolated cytoplasm “champagne bubble cytoplasm” which was suspicious for metastatic renal cell carcinoma. The patient subsequently underwent thyroidectomy with positive staining for RCC and PAX8 by immunohistochemistry, confirming metastatic renal cell carcinoma.
Discussion : The risk of malignancy in thyroid nodules identified on PET-CT is reported between 27.8-74.0 % and nodules with higher SUV have a higher likelihood of malignancy. The overall incidence of metastatic disease to the thyroid gland is approximately 2% in autopsy series. The most common primary malignancy in cases of metastatic disease to the thyroid is renal cell carcinoma followed in descending order by lung malignancy, gastrointestinal malignancies, and breast cancer. In our patient, both PET-avidity and presence of microcalcifications in the thyroid nodule suggested a high risk of malignancy.
Conclusion : This case highlights the importance of high clinical suspicion in patients with PET-avid thyroid nodules, especially those with a past history of malignancy. Such patients should undergo fine-needle aspiration to evaluate for possible malignancy given the high pre-test probability.
Walter Reed National Military Medical Center
Walter Reed Endocrinology Fellow