■ Diffuse Changes

Diffuse thyroid changes are associated with changes in the size and/or structure of the organ. The enlarged thyroid may show a normal, hyperechoic, or hypoechoic structure, whereas the diffuse structural changes in a normal-sized thyroid are hypoechoic, with few exceptions (e. g., radiation-induced hypothyroidism). Aside from goiters composed of multiple confluent hypoechoic nodules, these

Enlarged Thyroid Gland

diffuse hypoechoic changes always have an inflammatory, immunogenic, or autoimmune etiology.

Micro-, macroand normal-sized follicles as well as blood vessels determine the normal echo structure of the thyroid gland. Changes in the dominant follicle type lead to changes in this echo structure. It is best to evaluate the thyroid structure in relation to the surrounding

Fig. 14.6a and b Lateral to the thyroid gland (TH) are the internal jugular vein (VJ)—in this case markedly dilated with slow flow due to cardiac congestion—and, posterolaterally, the common carotid artery (AC).

Fig. 14.7 Superior thyroid artery (A) in the upper part of the thyroid gland (TH). M = musculature.

f Fig. 14.8 Inferior thyroid artery (ATI) at the lower pole of the thyroid gland (TH). AC = common carotid artery; M = anterolateral neck muscles.

musculature; otherwise the evaluation is subject to substantial errors. The normal thyroid tissues are more echogenic than the surrounding muscles (Fig.14.4). Several factors determine the echogenicity of the thyroid: the dominant follicle type (see Table 14.2, p. 492), vascularity, inflammation, and any regressive changes that have occurred.

Thyroid Gland

Diffuse Changes

Enlarged Thyroid Gland

Small Thyroid Gland

Hypoechoic Structure

Hyperechoic Structure

Circumscribed Changes

Differential Diagnosis of Hyperthyroidism

Diffuse Parenchymatous Goiter Diffuse Colloid Goiter

Hypertrophic Hashimoto Thyroiditis Hyperthyroidism due to Graves Disease Subacute de Quervain Thyroiditis

Invasive Sclerosing Thyroiditis (Riedel Goiter) Goiter in Acromegaly

Amyloidosis

Diffuse Colloid Goiter

Once hyperplasia of the thyroid has established a hormonal equilibrium, additional colloid storage occurs, causing an irregular increase in the size of the follicles. These macrofollicles and their colloid contents alter the structure of the gland, increasing its echogenicity (Fig.14.10). Sonographically, then, the diffuse colloid goiter appears as an enlarged thyroid gland with a homogeneous hyperechoic structure. This ultrasound finding, with a normal TSH level, justifies the initiation of treatment without further diagnostic tests.

Treatment of Diffuse Goiter

Iodine therapy,2 400 (to 500) g/day for 1 year, then the following maintenance

Pregnant or lactating women

230–260 g/day

Fig. 14.10 Diffuse colloid goiter: enlarged, hyperechoic thyroid (SieScape panoramic image).

Hashimoto thyroiditis is a type of autoimmune thyroid disease and the leading cause of acquired thyroid hypofunction. A rare hypertrophic form of this disease is distinguished from an atrophic form. Thyroiditis is a general term that refers to inflammation of the thyroid gland. Hashimoto thyroiditis, a chronic lymphocytic form with and without goiter is the most common cause of hypothyroidism in the United States and results in Hashimoto thyroiditis, atrophic autoimmune thyroiditis, and primary myxedema.

Sonographic features. In both the rare hypertrophic form and the atrophic form of autoimmune Hashimoto thyroiditis, ultrasound demonstrates a homogeneous, very echopenic organ that appears isoechoic to the surrounding muscles and has a bulky, often asymmetrical shape. Color duplex examination reveals an intense, speckled hypervascular pattern that is chiefly responsible for the hypoechoic structure (Figs.14.11, 14.19, 14.20).

This condition is also commonly known as Graves disease. The term “immunogenic hyperthyroidism” expresses both the autoimmune etiology of the disease and the hyperthyroid state. The hyperthyroidism is frequently associated with extrathyroid manifestations such as endocrine ophthalmopathy and pretibial myxedema. Younger women are predominantly affected. Graves disease is the most frequent cause of hyperthyroidism in adolescents. Diagnosis is generally based on the clinical presentation and laboratory findings (autoantibody detection).

Sonographic features. Ultrasound shows a marked volume increase (up to 90 mL) and symmetrical enlargement of the thyroid. The enlargement includes the isthmus, and this is considered a significant criterion for the disease. The thyroid acquires a rounded, balloonlike appearance (Fig.14.12). The volume dwindles during remissions and increases during recurrences. Because of the rich blood supply, the thyroid shows a diffuse decrease in echogenicity with densely packed hypoechoic areas, resulting in a hypoechoic internal structure.3

Diagnosis of Graves Hyperthyroidism

Clinical features. The typical clinical symptoms present as the classic triad of goiter, exophthalmos, and tachycardia, described by Karl von Basedow in 1840 and Robert Graves in 1835.

Laboratory findings. The hyperthyroidism is confirmed by in-vitro suppression tests showing low TSH and elevated free T4 and T3. Since isolated T3 hyperthyroidism can occur, a T4 determination is insufficient in itself.

TRAbs. Autoantibodies against the TSH receptor (TRAbs) exert a TSH-like effect that directly stimulates the thyrocytes and pro-

Color Doppler examination. Given the hypervascularity that underlies the characteristic echo structure, color Doppler reveals intense color-flow signals throughout the organ, creating a pattern described as a “thyroid inferno”3 or “vascular inferno” (Fig.14.13, Fig.14.14).

duces a diffuse hyperplasia and hypertrophy of the thyroid follicular epithelium. TRAbs are positive in 90% of patients with Graves disease. They are still positive in 46% of cases following radioiodine therapy and in 2% following excision of a goiter.4

Anti-TPO. Besides TRAbs, low titers of antithyroid peroxidase antibodies (anti-TPO, formerly microsomal antibodies) are found in 76% of cases.

The diagnosis is definite when signs of endocrine ophthalmopathy are seen. Other than thyroid ultrasound, there is no need for further testing.

The internal hypervascularity does not correlate with functional status, however;5 it is due chiefly to inflammation. But the density of the color pixels does correlate strongly with the need for thyrostatic treatment. Another indication for color duplex examination is follow-up, because thyroid blood flow is

significantly higher in patients with a recurrence, and therefore vascularity becomes an important prognostic indicator. The peak flow velocity is also markedly increased to more than 100 cm/s (normal flow velocity 20–40 cm/s) (Fig.14.15). This is best demonstrated by Doppler sampling of the inferior thyroid artery.

Differentiation from autoimmune thyroiditis.

Autoimmune thyroiditis has a similar hypoechoic structure, but Graves goiter is distinguished by a coarser hypoechoic pattern, a more rounded shape due to concomitant isthmic enlargement, and more intense vascularity with a high arterial flow velocity. Autoimmune thyroiditis also shows marked hypoechoicity, but the vascularity on color duplex examination is less pronounced and has a finer texture.

Autonomous nodules. Autonomous nodules in a hyperthyroid Graves goiter, or Graves disease developing on the basis of a nodular goiter (Marine–Lenhart syndrome ( 14.4 p–r), may occur. Autonomous nodules and adenomas do not participate in the autoimmune changes in the Graves thyroid; this confirms their auton-

Fig. 14.14 Graves disease: patchy hypoechoic thyroid gland (TH), isoechoic to the muscle (M) (B-mode image corresponding to Fig. 14.13b).

omous growth and identifies them as true neoplasms in Graves goiters. At the same time, areas of regressive fibrosis may appear as focal lesions.

Diagnosis. The balloon-like shape, grainy hypoechoic texture, and intense vascularity are such typical sonographic features that, when hyperthyroidism is detected, ultrasound can

Fig. 14.15 Color Doppler with spectral analysis in Graves disease. The peak systolic flow velocity in the inferior thyroid artery (ATI) is greatly increased, measuring 1.55 m/s.

establish the diagnosis of Graves goiter even without serology.

Ultrasound yields a correct diagnosis in 74% of patients with Graves disease,6,7 radionuclide scanning in 96%. Given this high sensitivity of ultrasound and the reliability of serological testing, radionuclide scanning is indicated in Graves disease only in cases where ultrasound has additionally detected focal changes.

De Quervain thyroiditis is an acute or subacute viral thyroiditis. Histologically, this form of thyroiditis is distinguished by giant-cell–like granulomas and by scarring in the healing stage. This can also be demonstrated by ultrasoundguided fine-needle aspiration cytology.

Sonographic features. Sonographically, the thyroid enlargement is based mainly on an increase in AP diameter. The isthmus does not appear as prominent as in Graves disease. With regard to echo texture, this type of goiter is distinguished by its intensely hypoechoic structure with a coarse patchy, focal, or diffuse texture (Fig.14.16, Fig.14.17).

Symptoms of de Quervain Thyroiditis

Patients manifest the clinical signs of a viral infection (adenovirus, myxovirus, paramyxovirus) with general malaise, fever, an enlarged thyroid with local tenderness, and laboratory tests positive for inflammation. Patients often describe pain radiation to the neck region. Brief cortisone therapy

Color Doppler sonography. In color Doppler, de Quervain thyroiditis shows inside the hypoechoic parts little or no vascularity, which positively distinguishes it from Graves disease.

can bring dramatic improvement, but most cases resolve spontaneously over a period of weeks or months.

Hyperthyroidism (up to 50%) is often the dominant initial finding.

Contrast-enhanced ultrasound (CEUS) likewise demonstrates reduced vascularity. Unilateral focal lesions may occur (Fig.14.17b; see also

Fig.14.38, Fig.14.39).