Thyroid adenoma is one of the most common tumors in the neck. It is a tumor arising from follicular epithelium, accounting for 70%–80% of thyroid tumors. It can occur at any age but is more frequently observed in young women. Approximately 10% of thyroid adenomas can undergo malignant transformation, and 20% can lead to hyperthyroidism. Based on morphological characteristics, thyroid adenomas can be classified into follicular adenomas and papillary cystic adenomas. Follicular adenomas are more common, while papillary cystic adenomas are less frequent and typically more challenging to distinguish from papillary thyroid carcinoma.
Clinical Manifestations
Thyroid adenomas grow slowly and have a relatively long disease course, often occurring during periods of thyroid functional activity. They can remain asymptomatic for several years. During physical examinations, the tumor typically presents as a well-defined mass localized to one lobe of the thyroid gland. The mass is slightly firmer than the surrounding thyroid tissue, smooth in surface texture, painless, and moves vertically during swallowing. When intratumoral hemorrhage occurs, the tumor can rapidly enlarge over a short period, accompanied by localized pain and a sensation of fullness.
Diagnosis
For patients with a slow disease course, minimal symptoms, and a solitary, smooth-surfaced thyroid mass on one side of the neck, the possibility of a thyroid adenoma should be considered. Diagnosis can generally be made based on a combination of thyroid ultrasonography, CT, MRI, and other auxiliary tests.
Ultrasound is highly accurate and reproducible for diagnosing thyroid adenoma and serves as the first-choice diagnostic method. On ultrasound, thyroid adenomas typically appear as well-circumscribed lesions with a homogeneous internal texture, encapsulated, sometimes with a "halo" sign. Most adenomas are solid, while some may have a mixed solid and cystic component. Purely cystic adenomas are rare. They are more commonly hypoechoic or isoechoic but may also appear hyperechoic. CT and MRI are also useful for diagnosis. CT scans often show hypodense, round nodules with clear margins, distinctly outlined against the surrounding hyperdense normal thyroid tissue. MRI imaging reveals single, well-defined nodules with long T1 and long T2 signal intensities within the thyroid parenchyma. These nodules are round or oval in shape with homogeneous signal intensity. Additionally, fine-needle aspiration cytology (FNAC) can assist in preoperative diagnosis, though false negatives may occur. Definitive diagnosis ultimately requires pathological examination.
Treatment
Thyroid adenomas can result in hyperthyroidism or malignant transformation. The current treatment approach advocates for early surgical excision as a principle. The choice of the initial surgical method is crucial in reducing the risk of tumor recurrence and malignant transformation. Previously, some researchers recommended simple adenoma excision to preserve the posterior thyroid capsule and normal thyroid tissue as much as possible, thereby lowering the risk of intraoperative recurrent laryngeal nerve and parathyroid gland injury and minimizing postoperative complications. However, subsequent studies have indicated that early thyroid carcinoma may be difficult to differentiate from thyroid adenoma. If simple excision is performed, malignant transformation or recurrence of the tumor significantly increases the complexity of secondary surgery. Therefore, current surgical approaches for thyroid adenoma favor unilateral lobectomy or subtotal lobectomy, including the adenoma within the excision. If the adenoma is adjacent to the thyroid isthmus, unilateral thyroid lobectomy with isthmus excision may be performed. This approach is currently considered a safe, feasible, and effective method for treating thyroid adenomas.