The cause of this “stony hard” thyroid enlargement is poorly understood, but it shows similarities to other fibrosclerosis such as the retroperitoneal fibrosis in Ormond disease. In this type of goiter, inflammation spreads from an extrathyroid source to involve the thyroid gland and other tissues in the neck. It belongs in the broader category of immune thyroiditis because it is associated with lymphocytic infil-

trates and leads to scarring and the formation of hyaline connective tissue.

Sonographic features. The diffuse, intense hypoechoicity reflects both the presence of hypoechoic connective tissue and the inflamed condition of the thyroid, which shows a balloonlike enlargement similar to that in Graves disease (Fig.14.18).

Thyroid Gland

Diffuse Changes

Enlarged Thyroid Gland

Small Thyroid Gland

Hypoechoic Structure

Hyperechoic Structure

Circumscribed Changes

Differential Diagnosis of Hyperthyroidism

Acquired Autoimmune Thyroiditis (AIT): Atrophic Lymphocytic Thyroiditis (Juvenile)

Acquired Autoimmune Thyroiditis (AIT)

in Polyglandular Autoimmune Syndrome (PAS) Lithiumor Amiodarone-Induced Thyroiditis Neonatal Hypothyroidism

Postoperative Thyroid/Unilateral Aplasia Radioiodine-Treated Thyroid Radiation-Induced Hypothyroidism

Concept of Acquired Autoimmune Thyroiditis

oidism that is associated with type 1 diabetes and most commonly occurs in chil-

In the type II form of PGA, AIT and type 1 diabetes are accompanied by hypogonadism, myasthenia, vitiligo, and alopecia.

In type III PGA, type 1 diabetes is accompanied by an AIT or by adrenal insufficiency with Hashimoto AIT.

●Chronic thyroiditis (juvenile) with transient hyperthyroidism.

●Postpartum thyroiditis (see below).

●Other forms of AIT such as lithium-, amiodaroneor interferon-induced thyroiditis are probably separate entities that do not fall under the heading of Hashimoto thyroiditis.

Atrophic thyroiditis is responsible for most cases of silent hypothyroidism in adults, followed by hypothyroidism after a thyroid resection. The atrophic form is far more common than the classic Hashimoto thyroiditis associated with a goiter (see above).

Sonographic features. Ultrasound shows a markedly small thyroid, often asymmetrical, with a homogeneous grainy or patchy hypoechoic texture containing fine, hyperechoic areas of scarring. The scars may produce contour irregularities (Fig.14.19a, Fig.14.20a).

Color duplex examination shows a fine or coarse pattern of vascular signals that may still be very pronounced or already diminished owing to scarring (Fig. 14.19b, Fig.14.20b).

Scans at the end stage of myxedema may still show residual areas of thyroid tissue, whose volume is less than that of a normal thyroid lobe (Fig.14.21).

Fig. 14.19 Chronic atrophic initial stage-autoimmune Hashimoto thyroiditis. M = sternocleidomastoid muscle; I = isthmus with a section of muscle; TR = trachea.

a Transverse scan shows a hypoechoic background texture with small, hyperechoic inclusions, probably due to focal scarring.

b Longitudinal scan on the left side.

During surgical resection of the thyroid gland (strumectomy), the poles are exposed and the posterior portions of the gland are dissected free in the area of the recurrent nerve. The isthmus is resected first, followed by the other parts of the gland, leaving a remnant of thyroid tissue measuring approximately 2–4 cm × 2 cm × 2 cm. Nodular areas are resected completely.

Thus, a subtotal strumectomy leaves behind a greatly diminished residual gland that can be identified and measured sonographically (Fig.14.23).

When a total strumectomy is performed for thyroid carcinoma, all portions of the gland are resected after the recurrent nerve has been

dissected free. Ultrasound does not demonstrate a thyroid remnant in these cases.

In both operations, the parathyroid glands posterior to the upper and lower poles of the thyroid are left intact.

Unilateral aplasia is occasionally detected incidentally in adults (previous surgery should be excluded).