The normal thyroid gland is a fairly homogenous structure, but nodules often form within its substance. These nodules may be only the growth and fusion of localized colloid-filled follicles, or more or less discrete adenomas, or cysts. Nodules larger than 1 cm may be detected clinically by palpation. Careful examination discloses their presence in at least 4% of the general population. Nodules less than 1 cm in diameter and not clinically detectable unless located on the surface of the gland, are much more frequent. The terms adenomatous goiter, nontoxic nodular goiter, and colloid nodular goiter are used interchangeably as descriptive terms when a multinodular goiter is found.
The incidence of goiter, diffuse and nodular, is very much dependent on the status of iodine intake of the population. In areas of iodine deficiency, goiter prevalence may be very high and especially in goiters of longstanding, multinodularity developes frequently (see Chapter 20). The incidence of multinodular goiter in areas with sufficient iodine intake has been documented in several reports. In a comprehensive population survey of 2,749 persons in northern England, Tunbridge et al.1 found obvious goiters in 6.9% with a female/male ratio of 13:1.Single and multiple thyroid nodules were found in 0.8% of men and 5.3% of women, with an increased frequency in women over 45 years of age. Routine autopsy surveys and the use of sensitive imaging techniques produces a much higher incidence. In three reports nodularity was found in 30% to 60% of subjects in autopsy studies, and in 16% to 67% in prospective studies of randomly selected subjects on ultrasound.2 In Framingham the prevalence of multinodular goiter as found in a population study of 5234 persons over 60 years was 1%.3. Recent results from Singapore shows a prevalence of 2.8%.4 In an evaluation in 2,829 subjects, living in southwestern Utah and Nevada (USA between 31 and 38 years) of age, 2.3% had non-toxic goiter, including, 18 single nodules, 3 cysts, 38 colloid goiters and 7 without a histological diagnosis. No mention was made of multinodular goiters, although some might have been present in the colloid and unidentified group.5 In general, in iodine sufficient countries the prevalence of multinodular goiter goiter is not higher than 4 %.6