**4. Aetiology**

*Goiter - Causes and Treatment*

**2. Epidemiology**

**3. Risk factors**

4.European Thyroid Association guidelines for ultrasound malignancy risk

This chapter thus provides a comprehensive coverage of the topic with an

Thyroid nodules are a common finding in general population. This is likely due to the increased use of diagnostic imaging for purposes unrelated to the thyroid. The prevalence of thyroid nodules in a population depends on the screening method used and the presence of risk factors for nodule development. The prevalence of thyroid nodules by palpation was found to be 4.2% in a population-based study in Framingham. The prevalence in females and males was 6.4 and 1.5%, respectively [5]. Clinically nonpalpable nodules are frequently identified on ultrasonography and are termed "incidentalomas." The prevalence of thyroid nodules as detected by high resolution ultrasound can be as high as 67% [6]. The prevalence in this Californian study also had an asymmetrical distribution with 72 and 41% prevalence in females and males respectively. 22% patients had solitary nodules, whereas 45% had multiple nodules. In another Italian study by Bartollota et al., the prevalence of thyroid nodules by ultrasonography was 33.1%. Thus it becomes a difficult dilemma on what to do with incidentally detected thyroid nodules which

Also the number of detected nodules increases with age, with the highest prevalence in the seventh decade. Autopsy studies provide the true prevalence of the incidence in a population. An autopsy study in Mayo clinic revealed a prevalence of around 50% even in patients with no history of thyroid disease [7, 8]. This makes it even more complicated that many individuals would complete their lifespan

The prevalence of thyroid nodules is 4 times more common in females than in males. Gender disparity is postulated to occur secondary to influence of oestrogen and progesterone, as demonstrated by increased risk associated with pregnancy and multiparity [9]. The prevalence of thyroid nodules increases with age. Nodules occur more commonly in areas of iodine deficiency. Cigarette smoking can also predispose to development of nodular goitre. This can occur secondary to inhibition of iodine uptake and organification by thiocyanate, which is derived from cyanide in cigarette smoke, hence mimicking iodine deficiency [10]. Obesity has also been demonstrated to be associated with increased risk of goitre and thyroid nodules [11, 12]. Serum IGF-1, being a potent mitogenic factor, was postulated to be associated with development of thyroid nodules. A positive association was observed between serum IGF-1 levels and prevalence of thyroid nodules in males in a study by Volzke et al. In a study by Ying Jian Liu et al., serum IGF-1 levels were not found to be significantly different in patients with hot nodules, cystic cold and solid cold nodules. However, in subgroup analysis, patients with thyroid adenoma on FNA were found to be having significantly higher serum IGF1 levels compared to the control group comprising of healthy adults. However no such association was demonstrated in a study by Hsiao et al. [13–15]. On the other hand, alcohol intake has been associated with decreased prevalence of goitre and thyroid nodules [16].

stratification of thyroid nodules in adults: The EU-TIRADS [4].

optimal approach in management of a thyroid nodule.

are not malignant and not well-characterised.

without any intervention for their thyroid nodules.

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Thyroid nodular disease comprises of a wide range of disorders. Colloid nodules, cysts and thyroiditis comprise of 80% of cases, whereas benign follicular neoplasms and thyroid carcinomas account for 10–15% and 5% cases respectively [20]. These causes have been summarised in **Table 1**.


**Table 1.**

*Aetiology of thyroid nodules.*
