Hürthle Cell Neoplasms: A New Differential Diagnosis for 18F-FDOPA-avid Thyroid Nodules?

Abstract

We report the case of a 54-year-old woman who presented with a 33-mm left adrenal mass on surveillance 7 years after a primary breast cancer. She had no symptoms of catecholamine excess, but the comprehensive hormonal testing identified an elevation of the 24-hour urinary normetanephrine (4950 mmol, upper reference limit [URL], 2200) and metaphrine (7462 mmol, URL 1500) levels as well as serum chromogranin A (120 g/L, URL 100). Serum calcitonin and other parameters were all in the normal range. The computed tomography (CT)/magnetic resonance imaging scans were consistent with a pheochromocytoma. F-Fluorodihydroxyphenylalanine (F-FDOPA) positronemission tomography/CT identifieda typicalhighly avid pheochromocytoma (maximum standardized uptake value [SUVmax], 9.4) but also an additional F-FDOPAavid thyroid nodule (SUVmax, 3.9) (Figure 1, A, B, and E). F-Fluorodeoxyglucose positron emission tomography/CT showed the pheochromocytoma (SUVmax, 4.2) but failed to detect the thyroid lesion, which was therefore not consistent with the diagnosis of a paraganglioma or pheochromocytoma metastasis (Figure 1, C and F). Thyroid color Doppler ultrasound showed a 22-mm left thyroid lobe nodule with central/ peripheralhypervascularity (Figure1D).Fine-needleaspiration cytology of the left thyroid nodule revealed a macrofollicular nodule (Bethesda class II), which ruled out nonsecreting medullary thyroid carcinoma despite F-FDOPA uptake (1). The serum TSH level was normal, and serum thyroid autoantibodies were undetectable. An uneventful left laparoscopic adrenalectomy was performed, and histology confirmed a pheochromocytoma (Pheochromocytoma of the Adrenal gland Scaled Score, PASS 0). A diagnostic left thyroid lobectomy was performed separately, and pathological examination found a Hurthle cell adenoma (Figure 1G). It has been previously documented that Hurthle cell neoplasms may be detected by various other radiopharmaceuticals (2–4). This episode suggests that Hurthle cell lesions need to be included in the differential diagnosis of F-FDOPA-avid thyroid nodules. The uptake of F-FDOPA remains currently unexplained. It may be related to an overexpression of L-type amino acid transporter 1, which may potentially play a role in the development of tumors (5).