Thyroid nodules
Introduction
Thyroid nodules are discrete lesions within the thyroid gland that are radiologically distinct from the surrounding thyroid parenchyma. They are relatively common, with a prevalence that increases with age. While most thyroid nodules are benign, a small percentage can be malignant, necessitating careful evaluation and management.
Epidemiology
Thyroid nodules are detected in approximately 4-7% of the adult population through palpation, while ultrasonography reveals nodules in up to 67% of individuals. The incidence of thyroid nodules is higher in women and increases with age. Other risk factors include a history of radiation exposure, iodine deficiency, and a family history of thyroid disease.
Pathophysiology
Thyroid nodules can arise from various pathophysiological processes, including hyperplasia, cyst formation, inflammation, and neoplasia. The majority of benign nodules are colloid nodules, which result from focal hyperplasia of thyroid follicular cells. Other benign lesions include thyroid cysts, which are fluid-filled cavities within the gland, and thyroiditis, an inflammatory condition.
Malignant thyroid nodules can be classified into several types, including papillary thyroid carcinoma, follicular thyroid carcinoma, medullary thyroid carcinoma, and anaplastic thyroid carcinoma. Each type has distinct histopathological features and clinical behavior.
Clinical Presentation
Most thyroid nodules are asymptomatic and are discovered incidentally during physical examination or imaging studies for unrelated conditions. When symptoms do occur, they may include a palpable neck mass, dysphagia, dyspnea, hoarseness, or pain. Symptoms are more likely to be present in larger nodules or those causing compression of adjacent structures.
Diagnostic Evaluation
The evaluation of a thyroid nodule typically begins with a thorough history and physical examination. Important historical factors include rapid growth of the nodule, a history of radiation exposure, and family history of thyroid cancer.
Imaging
Ultrasonography is the primary imaging modality for evaluating thyroid nodules. It provides detailed information about the size, composition, and echogenicity of the nodule, as well as the presence of suspicious features such as microcalcifications, irregular margins, and increased vascularity.
Fine-Needle Aspiration Biopsy
Fine-needle aspiration biopsy (FNAB) is the most accurate and cost-effective method for evaluating the cytology of thyroid nodules. FNAB can distinguish between benign and malignant lesions and guide further management. The Bethesda System for Reporting Thyroid Cytopathology is commonly used to categorize FNAB results.
Molecular Testing
Molecular testing can be used to evaluate indeterminate FNAB results. Tests for genetic mutations and rearrangements, such as BRAF, RAS, RET/PTC, and PAX8/PPARγ, can provide additional information about the likelihood of malignancy.
Management
The management of thyroid nodules depends on the results of the diagnostic evaluation.
Benign Nodules
Benign nodules are typically managed with observation and periodic follow-up. Serial ultrasonography is used to monitor for changes in size or appearance. In some cases, symptomatic benign nodules may be treated with thyroid hormone suppression therapy or minimally invasive procedures such as ethanol ablation or radiofrequency ablation.
Malignant Nodules
Malignant nodules require surgical intervention, usually in the form of a thyroidectomy. The extent of surgery depends on the type and stage of the cancer. Total thyroidectomy is often performed for more aggressive cancers, while lobectomy may be sufficient for smaller, well-differentiated tumors.
Postoperative management may include radioactive iodine therapy, thyroid hormone replacement, and regular monitoring for recurrence.
Prognosis
The prognosis for patients with thyroid nodules varies depending on the nature of the nodule. Benign nodules generally have an excellent prognosis with minimal risk of complications. The prognosis for malignant nodules depends on the type and stage of the cancer, with papillary and follicular carcinomas having the best outcomes and anaplastic carcinoma having the poorest prognosis.