Thyroid nodules: Clinical sciences

Thyroid nodules are discrete, solid, or fluid-filled lumps in the thyroid gland, often found incidentally on exam or imaging. Thyroid nodules are common and usually benign, though some can be malignant. When evaluating a thyroid nodule, you will want to determine if the patient has thyroid dysfunction and obtain a thyroid ultrasound. Patients who are hypothyroid or euthyroid require further work up based on concerning features on ultrasonography, while patients who are hyperthyroid will require a radioactive iodine uptake or RAIU test.

Alright, when a patient presents with chief concern suggesting thyroid nodule, you should first perform a focused history and physical examination. Most patients with thyroid nodules are asymptomatic and the nodule is found on a routine exam or incidentally on imaging. If the patient does have symptoms, they may have signs of hyperthyroidism, such as tachycardia, weight loss, muscle weakness, heat intolerance, anxiety, or irritability; or signs of hypothyroidism like dry skin, depression, cold intolerance, fatigue, and constipation. Very rarely, if the nodule is large enough, it can put pressure on surrounding structures and cause symptoms, like a feeling of fullness in the throat or difficulty swallowing.

You should also assess for personal or family history of syndromes that increase the risk of developing cancer. This includes Cowden disease; familial adenomatous polyposis or FAP; multiple endocrine neoplasia or MEN II; Carney complex; or Werner syndrome, also called progeria.

Meanwhile, on physical examination, you may feel the nodule as a palpable mass at the front of the neck, over the thyroid. Remember, the thyroid moves upward when the patient swallows, so if the nodule you feel also moves upward, you know it is part of the thyroid. If the nodule doesn’t move upward with swallowing, then it’s another type of neck mass. Now, in some cases, you may feel more than one nodule, what’s known as a multinodular thyroid, and you might even find palpable cervical lymph nodes.

Alright, if you see these findings, you should next assess for thyroid dysfunction by ordering TSH and obtain a thyroid ultrasound.

Okay, let’s start with patients who are hypothyroid, meaning their TSH is elevated, and patients who are euthyroid, meaning their TSH is within reference range. In these cases, the nodule is not producing thyroid hormone, so it’s a non-functioning thyroid nodule. If this is the case, you will want to assess your ultrasound results to help you determine the risk for malignancy.

If the ultrasound shows a cystic mass that’s smaller than 1 cm in size, you should have a low suspicion for malignancy, and can consider the nodule a benign thyroid nodule. Benign nodules are commonly found in some thyroid conditions like Hashimoto thyroiditis, subacute thyroiditis, colloid nodules, and follicular adenomas. These patients need a repeat ultrasound at 12 to 24 months for follow up. Now, here’s a high-yield fact! If an ultrasound shows a cystic lesion with solid components, this is more likely to be malignancy, and so you should proceed with a fine needle aspiration, or an FNA. On the other hand, if the ultrasound shows a hypoechoic, solid mass, that’s 1 cm in size or larger, with microcalcifications, irregular margins, hypervascularity, evidence of extrathyroidal extension, and a taller than wide shape, you should have an intermediate to high suspicion for malignancy. In this situation, you need to order an FNA for cytological analysis.

Here’s a clinical pearl! FNA cytology uses the Bethesda System for cytopathology. There are six classifications based on cytology results, including nondiagnostic or unsatisfactory; benign; atypia or follicular lesion of undetermined significance, also called AUS or FLUS respectively; follicular neoplasm or suspicious for follicular neoplasm; suspicious for malignancy; and lastly, malignant.