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INTRODUCTION

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APPROACH TO THE PATIENT: A Thyroid Nodule

Palpable thyroid nodules are found in about 5% of adults, but the prevalence varies considerably worldwide. Given this high prevalence rate, practitioners commonly identify thyroid nodules. The main goal of this evaluation is to identify, in a cost-effective manner, the small subgroup of individuals with malignant lesions.

Nodules are more common in iodine-deficient areas, in women, and with aging. Most palpable nodules are >1 cm in diameter, but the ability to feel a nodule is influenced by its location within the gland (superficial versus deeply embedded), the anatomy of the patient's neck, and the experience of the examiner. More sensitive methods of detection, such as computed tomography (CT), thyroid ultrasound, and pathologic studies, reveal thyroid nodules in >20% of glands. The presence of these thyroid incidentalomas has led to much debate about how to detect nodules and which nodules to investigate further. Most authorities still rely on physical examination to detect thyroid nodules, reserving ultrasound for monitoring nodule size or as an aid in thyroid biopsy.

An approach to the evaluation of a solitary nodule is outlined in Fig. 48-1. Most patients with thyroid nodules have normal thyroid function tests. Nonetheless, thyroid function should be assessed by measuring a thyroid-stimulating hormone (TSH) level, which may be suppressed by one or more autonomously functioning nodules. If the TSH is suppressed, a radionuclide scan is indicated to determine if the identified nodule is "hot," as lesions with increased uptake are almost never malignant and fine-needle aspiration (FNA) is unnecessary. Otherwise, FNA biopsy, ideally performed with ultrasound guidance, should be the first step in the evaluation of a thyroid nodule. FNA has good sensitivity and specificity when performed by physicians familiar with the procedure and when the results are interpreted by experienced cytopathologists. The technique is particularly useful for detecting papillary thyroid cancer (PTC). The distinction between benign and malignant follicular lesions is often not possible using cytology alone.

In several large studies, FNA biopsies yielded the following findings: 70% benign, 10% malignant or suspicious for malignancy, and 20% nondiagnostic or yielding insufficient material for diagnosis. Characteristic features of malignancy mandate surgery. A diagnosis of follicular neoplasm also warrants surgery, as benign and malignant lesions cannot be distinguished based on cytopathology or frozen section. The management of patients with benign lesions is more variable. Many authorities advocate TSH suppression, but others monitor nodule size without suppression. With either approach, thyroid nodule size should be monitored, ideally using ultrasound. Repeat FNA is indicated if a nodule enlarges, and a second biopsy should be performed within 2–5 years to confirm the benign status of the nodule.

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FIGURE 48-1

Approach to the patient with a thyroid nodule. See text and references for details. *About one-third of nodules are cystic or mixed solid and cystic. FNA, fine-needle aspiration; TSH, thyroid-stimulating hormone; US, ultrasound.

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