Diagnostic ultrasound ( PDFDrive )

724 PART III Small Parts, Carotid Artery, and Peripheral Vessel Sonography
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FIG. 19.44 Focal Areas of Subacute Thyroiditis. (A)
Longitudinal power Doppler image of the thyroid gland shows
two poorly deined hypoechoic areas (arrows) caused by
subacute thyroiditis at ine-needle aspiration. (B) Longitudinal
image of a different patient shows poorly deined hypoechoic
area (arrows). (C) This area has returned to normal on
follow-up examination 4 weeks later after medical therapy.
infection and afecting children. Sonography can be useful in
select patients to detect the development of a frank thyroid abscess.
he infection usually begins in the perithyroidal sot tissues. On
ultrasound images, an abscess is seen as a poorly deined,
hypoechoic heterogeneous mass with internal debris, with or
without septa and gas. Adjacent inlammatory nodes are oten
present.
Subacute granulomatous thyroiditis or De Quervain disease
is a spontaneously remitting inlammatory disease probably
caused by viral infection. he clinical indings include fever,
enlargement of the gland, and pain on palpation. Sonographically,
the gland may appear enlarged and hypoechoic, with normal or
decreased vascularity caused by difuse edema of the gland, or
the process may appear as focal hypoechoic regions 147,148 (Fig.
19.44). Although usually not necessary, sonography can be used
to assess evolution of de Quervain disease ater medical therapy.
he most common type of thyroiditis is chronic autoimmune
lymphocytic thyroiditis, or Hashimoto thyroiditis. It typically
occurs as a painless, difuse enlargement of the thyroid gland in
a young or middle-aged woman, oten associated with hypothyroidism.
It is the most common cause of hypothyroidism in
North America. Patients with this autoimmune disease develop
antibodies to their own thyroglobulin as well as to the major
enzyme of thyroid hormonogenesis, thyroid peroxidase. he
typical sonographic appearance of Hashimoto thyroiditis is difuse,
coarsened, parenchymal echotexture, generally more hypoechoic
than a normal thyroid 144 (Fig. 19.45). In most cases the gland is
enlarged. Multiple, discrete hypoechoic micronodules from 1
to 6 mm in diameter are strongly suggestive of chronic thyroiditis;
this appearance has been called micronodulation (see Fig. 19.45,
Video 19.7). Micronodulation is a highly sensitive sign of chronic
thyroiditis, with a positive predictive value of 94.7%. 149 Histologically,
micronodules represent lobules of thyroid parenchyma that
have been iniltrated by lymphocytes and plasma cells. hese
lobules are surrounded by multiple linear echogenic ibrous
septations (Fig. 19.46). hese ibrotic septations may give the
parenchyma a “pseudolobulated” appearance. Both benign and
malignant thyroid nodules may coexist with chronic lymphocytic
thyroiditis, and FNA is oten necessary to establish the inal
diagnosis 150 (Figs. 19.47 to 19.49). As with other autoimmune
disorders, there is an increased risk of malignancy, with a B-cell
malignant lymphoma most oten arising within the gland.
he vascularity on color Doppler imaging is normal or
decreased in most patients with the diagnosis of Hashimoto
thyroiditis (see Fig. 19.45). Occasionally, hypervascularity similar
to the “thyroid inferno” of Graves disease occurs. One study