Question

What is the difference between hypoechoic halo and hypoechoic us characteristic nodule in thyroid?

Answer 1

Replacing palpating fingers with an ultrasound (US) probe has resulted in an epidemic of thyroid nodules. Despite the high prevalence of thyroid nodules in the general population, thyroid malignancy is rare. Although no imaging modality can accurately predict the nature of every nodule, high-resolution US is the most sensitive, easily available and cost-effective diagnostic test available to detect thyroid nodules, measure their dimensions and identify their structure. The presence of calcifications, irregular spiculated outline, hypoechogenicity in a solid nodule, chaotic intranodular vascularity and an elongated shape are well-known US features of malignancy in thyroid nodules. Cervical lymph node metastasis and extrathyroidal extension of a thyroid nodule are highly specific for malignancy but seen infrequently. Spongiform nodules, purely or predominantly cystic nodules, nodules with well-defined hypoechoic halo and echogenic as well as isoechoic nodules are usually benign. None of the US characteristics have 100% accuracy in detecting or excluding malignancy. Fine-needle biopsy is currently the best triage test for pre-operative evaluation of a thyroid nodule. There is no significant difference in the risk for malignancy between palpable and non-palpable nodules and size is not a reliable indicator for their malignant potential. The best tool for risk stratification for malignancy in thyroid nodules is US and guided biopsy of nodules with suspicious imaging features. This is especially relevant in patients with multinodular goitre.

Keywords: Thyroid nodule, ultrasound, risk stratification, thyroid biopsy

Introduction

Over the last 2 decades, replacing the palpating fingers with an ultrasound (US) probe has resulted in an epidemic of thyroid nodules. Sub-centimetre thyroid nodules are not usually detected at palpation. In comparison, high-resolution US accurately demonstrates nodules as small as 1–2 mm. Hence, the prevalence of thyroid nodules in the general population goes up from 8% to 76% when evaluated with US instead of clinical examination[1–3]. Even at autopsy, the prevalence of thyroid nodules is high with multiple thyroid nodules seen in 37.3% and solitary nodules found in 12.2% of random autopsies[4]. Thyroid nodules are ubiquitous but thyroid malignancy is rare with just 1 of 20 clinically detected nodules being malignant. This corresponds to approximately 2 to 4 cases per 100,000 people per year, constituting only 1% of all cancers and 0.5% of all cancer deaths[5]. This justifies against the use of screening US for thyroid nodules in the general population. Controversy exists in many areas of management of thyroid nodules, including the most cost-effective approach in their diagnostic evaluation. Practice guidelines from several expert groups such as the American Association of Clinical Endocrinologists, the American Thyroid Association and the Society of Radiologists in Ultrasound attempt to address them. However, there is still a lack of consensus on certain key areas.

Evaluation of thyroid nodules

A thyroid nodule is defined as a discrete lesion within the thyroid gland that is radiologically distinct from the surrounding thyroid parenchyma[6] (Fig. 1). Pathologically, they are classifiable into 5 types with distinct histologic features: hyperplasic, neoplastic, colloid, cystic and thyroid nodules[7]. Fundamental to their evaluation is differentiating medical from surgical disease and identifying the odd malignant one. Clinical information may often give a clue to this. Nodules increasing in size are suspicious for malignancy, but lesions with rapid increase in size over a few hours are likely to be haemorrhagic. Haemorrhagic changes are more commonly encountered in malignant than benign nodules[8]. A benign multinodular goitre (MNG) grows in size over the years but malignancy typically grows in weeks. Rapid