Diagnostic ultrasound ( PDFDrive )

CHAPTER 48 The Pediatric Head and Neck 1643
TABLE 48.2 Volume of Thyroid Gland
and Thickness of Each Lobe a
Height
(cm)
No. of
Subjects
Volume
(cm)
RLT
(cm) b
LLT (cm) b
≤99 16 2.3 ± 0.7 0.8 ± 0.17 0.8 ± 0.18
100-109 34 3.3 ± 1.0 0.8 ± 0.19 0.8 ± 0.21
110-119 35 4.1 ± 1.1 0.9 ± 0.17 0.9 ± 0.19
120-129 45 4.9 ± 1.1 0.9 ± 0.18 0.9 ± 0.20
130-139 36 6.3 ± 2.0 0.9 ± 0.25 1.0 ± 0.25
140-149 42 7.4 ± 2.2 1.0 ± 0.23 1.0 ± 0.23
150-159 59 8.5 ± 2.3 1.1 ± 0.23 1.0 ± 0.24
≥160 20 10.9 ± 2.5 1.2 ± 0.24 1.2 ± 0.25
a As a function of body height.
b Mean ±1 standard deviation.
LLT, Left lobe thickness; RLT, right lobe thickness.
With permission from Ueda D. Normal volume of the thyroid gland in
children. J Clin Ultrasound. 1990;18(6):455-462. 85
FIG. 48.25 Thyroid Hemiagenesis. Normal right lobe and isthmus
of the thyroid are identiied, but the left lobe is absent. Note that the
left carotid vessel lies in the anatomic area of the left lobe.
hypothyroidism, and transient elevated thyrotropin. 88,89 Rarely
(0.2% of cases), thyroid hemiagenesis can occur, with failure
of development in either lobe, the let being absent in 60% of
cases 88,90 (Fig. 48.25). On ultrasound, if no thyroid gland can be
identiied in the expected location, imaging should be performed
superiorly in the midline to the base of the tongue because ectopic
thyroid tissue may be present anywhere along the embryologic
descent. Ectopic thyroid tissue is lingual and thus suprahyoid
in 90% of cases, lying close to the hyoid bone and deep to the
muscles of the tongue. 90 Ultrasound imaging in the neonate with
ectopic thyroid typically shows a well-deined ovoid structure
equal in echotexture to normal thyroid tissue and hyperemic on
color Doppler (Fig. 48.26). In older children treated for hypothyroidism
in the presence of ectopic tissue, the gland may appear
hypoechoic with no vascularity. 91 Some children with ectopic
tissue are euthyroid and have a mass at the base of the tongue.
It is important to identify this tissue as thyroid because removal
in the absence of other thyroid tissue will result in a hypothyroid
individual. When ultrasound is unable to identify ectopic thyroid
tissue, a nuclear medicine scan, given the high sensitivity, may
be employed. 91,92 Scintigraphic studies are also useful in assessing
thyroid function when apparently normal thyroid tissue is
identiied on ultrasound. 89
hyroglossal duct cyst, representing 70% of all congenital
neck masses, is the most common midline cyst and developmental
anomaly identiied on ultrasound. 43,90,93 he anatomy of the
thyroglossal duct follows the pathway of embryology from the
foramen cecum of the tongue, along the inferior and posterior
surface of the midline hyoid, to the pyramidal lobe of the thyroid.
Persistence of the duct, which is lined by secretory epithelium,
results in cyst or sinus formation. he classic presentation of a
thyroglossal duct cyst is that of an asymptomatic mass adjacent
to the hyoid bone, although the cyst can be located at any point
of descent. 49,94 Anatomically, most are located in a midline or
parasagittal position, particularly to the let of midline. he
thyroglossal duct cyst may move with swallowing, and if suprahyoid,
the lesion will classically elevate with tongue movement. 43
Congenital istulas in association with these cysts are infrequent
but can occur ater inlammation. 95
he classic sonographic appearance of a thyroglossal duct cyst
is noted in less than half of cases and includes a thin-walled,
anechoic unilocular cyst (Fig. 48.27). Typically, however, these
cysts are caused by high protein content rather than inlammation
so they are hypoechoic or heterogeneous, some appearing
pseudosolid and mimicking ectopic tissue 95-97 (Fig. 48.28).
Posterior acoustic enhancement is present in most cysts, and
absence of color Doppler low can be helpful in the diagnosis.
However, demonstration of a normal thyroid gland while imaging
a thyroglossal duct cyst is recommended to exclude the diagnosis
of ectopic tissue. Up to one-third of patients with these cysts
will develop superimposed infection and demonstrate imaging
indings of thick walls, internal septation, and heterogeneous
echotexture from debris. 95,98 here is a slightly increased
risk of cancer, primarily papillary, and calciication or a sot
tissue mass in the presence of a cyst should raise suspicion of
malignancy. 82,93,99 herapy is surgical resection with the Sistrunk
procedure, which involves excision of the cyst, the remnant
tract, and part of the hyoid bone. Recurrent thyroglossal duct
cysts occur ater a Sistrunk procedure in approximately 11%
of patients. 100
Diferential diagnosis for cystic lesions in the infrahyoid space
includes thyroglossal duct cyst, dermoid, epidermoid, branchial
cyst, lymphatic malformation, laryngocele, necrotic adenopathy,
teratoma, and thymic cyst.
Inlammatory Thyroid Disease
Acute bacterial infection of the thyroid is rare because the gland
is highly resistant to infection by virtue of its high iodine
content. 101,102 If present, infection is usually caused by staphylococci,
streptococci, or anaerobic bacteria. On sonography, the
gland demonstrates heterogeneous, poorly deined echotexture.
If the let lobe of the thyroid is abnormal, a congenital piriform
sinus, type III or IV branchial apparatus remnant, should be