Diagnostic ultrasound ( PDFDrive )

694 PART III Small Parts, Carotid Artery, and Peripheral Vessel Sonography
he sternohyoid and omohyoid muscles (strap muscles) are
seen as thin, hypoechoic bands anterior to the thyroid gland
(see Fig. 19.2). he sternocleidomastoid muscle is seen as a
larger oval band that lies lateral to the thyroid gland. An important
anatomic landmark is the longus colli muscle, located posterior
to each thyroid lobe, in close contact with the prevertebral space.
he recurrent laryngeal nerve and the inferior thyroid artery
pass in the angle among the trachea, esophagus, and thyroid
lobe. On longitudinal scans, the recurrent laryngeal nerve and
inferior thyroid artery may be seen between the thyroid lobe
and esophagus on the let and between the thyroid lobe and
longus colli muscle on the right. he esophagus, primarily a
midline structure, may be found laterally and is usually on the
let side. It is clearly identiied by the target appearance of bowel
in the transverse plane and by its peristaltic movements when
the patient swallows.
FIG. 19.4 Normal Thyroid Vascularity on Power Doppler
Ultrasound.
FIG. 19.5 Normal Inferior Thyroid Vein. Longitudinal power Doppler
image shows a large inferior thyroid vein with associated normal venous
spectral waveform.
CONGENITAL THYROID
ABNORMALITIES
Congenital conditions of the thyroid gland include aplasia of
one lobe or the whole gland, varying degrees of hypoplasia, and
ectopia (Fig. 19.6). Sonography can be used to help establish
the diagnosis of hypoplasia by demonstrating a diminutive gland.
High-frequency ultrasound can also be used in the study of
congenital hypothyroidism (CH), a relatively common disorder
occurring in about 1 in 3000 to 4000 live births. Determining
the cause of CH (dysgenesis, dyshormonogenesis, or pituitary
or hypothalamic hypothyroidism) is clinically important because
prognosis and therapy difer. Early initiation of therapy can
prevent mental retardation and delayed bone development. 10,11
Measurement of thyroid lobes can be used to diferentiate
aplasia (absent gland) from goitrous hypothyroidism (gland
enlargement). Radionuclide scans are more oten used to detect
ectopic thyroid tissue (e.g., in a lingual or suprahyoid
position).
NODULAR THYROID DISEASE
Many thyroid diseases can manifest clinically with one or more
thyroid nodules. Such nodules represent common and controversial
clinical problems. Epidemiologic studies estimate that
A
B
FIG. 19.6 Congenital Thyroid Abnormalities. (A) Hypoplasia of right thyroid lobe. C, Carotid artery; Tr, tracheal air shadow. (B) Ectopic
(sublingual) thyroid gland. Transverse ultrasound image inferior to the base of the tongue shows a U-shaped parenchymal structure.