Another pattern to recognize as a benign nodule is the “spongiform nodule” also described in the literature as honeycomb or puff pastry appearance. All of these descriptors refer to the multiple small cystic spaces separated by thin septations which is shown in Fig. 5.3. These are considered highly likely benign and occur secondary to hyperplasia. Occasionally, bright echogenic foci may be found in these nodules. This finding needs to be closely interrogated, as the small cystic areas may have a bright linear interface at the posterior back wall of the cystic area which is benign and not to be confused with the malignant microcalcifications found within the stroma of a solid thyroid nodule.

Another classic benign pattern is diffuse tiny hypoechoic nodules . Figure 5.4 demonstrates this classic appearance of Hashimoto’s thyroiditis also known as chronic lymphocytic thyroiditis. These nodules range in size from 1 to 6 mm which pathologically is related to a lymphoplasmacytic infiltrate and lymphoid follicles and may have intervening echogenic bands of tissue, which correspond to fibrosis pathologically. The gland is usually symmetrically involved. This appearance has a 95% positive predictive value for Hashimoto’s thyroiditis [1, 5]. Vascularity is not helpful as it may be normal, increased, or decreased. Nodules are also commonly associated with Hashimoto’s thyroiditis. Careful evaluation of each nodule is warranted as studies have shown an increased risk of papillary thyroid carcinoma around 16% as well as an association with primary thyroid lymphoma [6, 7]. Figure 5.5 demonstrates a widely accepted, but rarely seen, benign nodule pattern found in Hashimoto’s thyroiditis the giraffe pattern or giraffe hide. This is described as geographic areas of increased echogenicity which are bounded by thin intervening bands of hypoechogenicity similar to the color pattern seen on giraffes. The echogenic nodule seen in Fig. 5.6 is a variation of this benign process. Sometimes referred to as a “white knight,” this nodule pathologically represents a benign regenerative nodule of Hashimoto’s thyroiditis [2].There are also a few patterns associated with malignancy. The most common and well-known malignant pattern is that of a hypoechoic solid nodule with microcalcifications or punctate echogenic foci. This is shown in Fig. 5.7. The vast majority of papillary thyroid cancers are hypoechoic with a high sensitivity but low specificity as many benign nodules are also hypoechoic. Microcalcifications have a low sensitivity but high specificity. This has been shown in several meta-analyses [8, 9]. Combining these two features yields a combination that increases specificity for papillary thyroid carcinoma. The echogenic foci are secondary to tiny calcifications which may be psammoma bodies and/or amorphous calcium deposits. The psammoma bodies are likely secondary to necrotic cells causing calcium to laminate around this nidus. The amorphous calcifications may occur secondary to degeneration or fibrosis. Both are present in papillary thyroid carcinoma.

Another pattern associated with malignancy is a hypoechoic solid nodule with coarse calcification centrally as seen in Fig. 5.8. This example demonstrates a well-demarcated rim of a hypoechoic nodule with central dense calcification felt to be suggestive of medullary carcinoma. [1] However, as medullary carcinoma accounts for only 3–5% of all thyroid carcinoma, macrocalcifications are more commonly seen in papillary carcinoma, and this is likely secondary to conglomeration of microcalcifications [10]. It is important to note that the coarse calcification is also common in benign nodules and multinodular goiter which is dystrophic in etiology. Therefore, this combination of a hypoechoic nodule with coarse calcification is the worrisome pattern, and coarse calcification alone is not worrisome on its own.

These patterns have been shown to be specific when present, but not sensitive enough to pick up all malignancies or stratify all nodules. Therefore, many groups have sought to implement classification schemes to include more appearances and characteristics which have been called thyroid imaging reporting and data systems (TI-RADS).