Clinical vignette:
83-year-old man presented for evaluation of non-toxic multinodular
goiter. Medical history was significant for renal cell carcinoma (RCC)
metastatic to the hip treated with chemotherapy. A surveillance PET-CT
demonstrated an FDG-avid right-sided thyroid nodule with SUV of 4.58
(Fig 1). Thyroid ultrasound revealed a 2.2cm hypoechoic nodule in the
right mid-lobe with faint microcalcifications (Fig 2). The patient
denied dysphagia, neck radiation, or family history of thyroid cancer.
Thyroid function tests were normal. FNA showed cohesive groups of cells
with large nuclei, irregular nuclear contours, granular chromatin with
“champagne bubble cytoplasm” (Fig 3). Subsequent thyroidectomy
specimen was positive staining for RCC marker and PAX8 by
immunohistochemistry, confirming metastatic RCC.
Thyroid nodules are often incidentally found on imaging studies with an
estimated 25% incidence on neck CT scan (1). The risk of malignancy in
thyroid nodules identified on PET-CT is reported 27.8-74.0%, and
nodules with higher SUVs have a higher likelihood of malignancy (1). The
overall incidence of metastatic disease to the thyroid gland is
approximately 2% in autopsy series (2). The most common primary
malignancy in cases of thyroid metastases is RCC followed in descending
order by lung, gastrointestinal, and breast malignancies. In our
patient, both PET-avidity and presence of microcalcifications in the
thyroid nodule suggested a high risk of malignancy.
This case highlights the importance of high clinical suspicion in
patients with PET-avid thyroid nodules, especially those with a history
of malignancy. Such patients should undergo FNA to evaluate for
malignancy given the high pre-test probability.