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\begin{document}

\title{Metastatic Renal Cell Carcinoma in the Thyroid Gland}



\author[1]{Mark Cruz}%
\author[1]{Gregory Schmidt}%
\author[1]{Jeptha Johnson}%
\author[1]{Mohamed Shakir}%
\author[1]{Thanh Hoang}%
\affil[1]{Walter Reed National Military Medical Center}%


\vspace{-1em}



  
  \date{May 20, 2024}


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\selectlanguage{english}
\begin{abstract}
Thyroid nodules are often incidentally noted on imaging studies with an
estimated incidence of 25\% on neck CT scan. The presence of a PET-avid
thyroid nodule, especially in a patient with a history of malignancy,
should prompt evaluation with fine-needle aspiration to evaluate for
malignancy given the high probability.%
\end{abstract}%



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Title Page

Clinical Picture:

\textbf{Metastatic Renal Cell Carcinoma in the Thyroid Gland}

Mark M. Cruz, MD\textsuperscript{1}

Gregory S. Schmidt, MD\textsuperscript{1}

Jeptha T. Johnson, MD\textsuperscript{2}

Thanh D. Hoang, DO\textsuperscript{1}

Mohamed KM. Shakir, MD\textsuperscript{1}

(1) Division of Endocrinology, Department of Medicine

(2) Department of Pathology

Walter Reed National Military Medical Center

8901 Rockville Pike, Bethesda, Maryland 20889

Corresponding Author: Dr.~Thanh D. Hoang

Division of Endocrinology, Walter Reed National Military Medical Center,

8901 Wisconsin Ave,

Bethesda, MD 20889.

Email: thanh.d.hoang.mil@mail.mil

\textbf{Disclaimer:} The views expressed in this article are those of
the authors and do not reflect the official policy of the Department of
Army/Navy/Air Force, Department of Defense, or the U.S. Government.



\textbf{Key Clinical Message:}

Thyroid nodules are often incidentally noted on imaging studies with an
estimated incidence of 25\% on neck CT scan. The presence of a PET-avid
thyroid nodule, especially in a patient with a history of malignancy,
should prompt evaluation with fine-needle aspiration to evaluate for
possible malignancy given the high pretest probability.

\textbf{Key words:}

RCC, metastatic disease, PET-CT, fine-needle aspiration, thyroid

\textbf{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.

\textbf{Authors contribution statement:}

Mark M. Cruz, MD - Author

Gregory S. Schmidt, MD- Reviewer

Jeptha Johnson, MD -- Pathologist, provided the slides, reviewer

Thanh D. Hoang, DO- Reviewer

Mohamed KM Shakir -- Reviewer

\textbf{References:}

(1) Chun, A. R., Jo, H. M., Lee, S. H., Chun, H. W., Park, J. M., Kim,
K. J., \ldots{} Kim, B. Y. (2015). Risk of Malignancy in Thyroid
Incidentalomas Identified by Fluorodeoxyglucose-Positron Emission
Tomography. Endocrinology and Metabolism, 30(1), 71.

(2) Nixon, I. J., Coca-Pelaz, A., Kaleva, A. I., Triantafyllou, A.,
Angelos, P., Owen, R. P., Ferlito, A. (2016). Metastasis to the Thyroid
Gland: A Critical Review. Annals of Surgical Oncology, 24(6),
1533--1539.

\textbf{Abbreviations:}

RCC: renal cell carcinoma

PET-CT: positron emission tomography - computed tomography

FDG: fluorodeoxyglucose

SUV: standard uptake value

FNA: fine needle aspiration

\textbf{Figures Legend:}

Figure 1: PET-CT demonstrating an FDG-avid right-sided thyroid nodule
with a standard uptake value of 4.58

Figure 2: Thyroid ultrasound with a 2.2cm hypoechoic nodule in the right
middle lobe with faint microcalcifications

Figure 3: A cytology smear of the FNA demonstrating cohesive groups of
cells with large nuclei, irregular nuclear contours, granular chromatin
with finely vacuolated cytoplasm ``champagne bubble cytoplasm''\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/Fig-1-PET/Fig-1-PET}

\end{center}
\end{figure}\selectlanguage{english}
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\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/Figure-2-Thyroid-ultrasound/Figure-2-Thyroid-ultrasound}

\end{center}
\end{figure}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/Figure-3-Thyroid-FNA/Figure-3-Thyroid-FNA}

\end{center}
\end{figure}

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