Diagnostic ultrasound ( PDFDrive )

1642 PART V Pediatric Sonography
1
2
scm
4
3
FIG. 48.24 Normal Thyroid. Transverse sonogram of the thyroid
gland demonstrates homogeneous, increased echotexture compared
with the sternohyoid and sternothyroid (sm) muscles. Normal right lobe,
left lobe, and isthmus (i). Trachea (T) is midline and esophagus (E) is
posterior to left lobe. Common carotid artery (C) is present along the
peripheral margin.
FIG. 48.23 Deep Cervical Fascial Layers of Infrahyoid Space. Axial
diagram: 1, supericial; 2, middle (visceral); 3, deep; 4, carotid; scm,
sternocleidomastoid muscle.
trachea. 83 he common carotid arteries and internal jugular veins
are present on the lateral edges, and the cervical esophagus is
midline or to the let of the trachea. he thyroid gland contains
two lobes and is connected by an isthmus. In 50% of patients,
a pyramidal lobe extends superiorly from the isthmus. Four
parathyroid glands lie along the posterior surface of the thyroid
lobes.
Ultrasound is performed with the patient supine and the neck
slightly hyperextended. A high-frequency linear array transducer
(10-15 MHz) is necessary. 84 A standof pad may be helpful.
Longitudinal and transverse imaging of the entire thyroid tissue
should be performed. Doppler imaging may be considered in
the examination of masses or nodules. Adjacent neck structures,
especially the jugular chain and supraclavicular nodes, should
be imaged.
On ultrasound, the normal thyroid gland is homogeneous
and hyperechoic compared with adjacent muscle (Fig. 48.24).
he lobes of tissue are triangular on transverse and elliptical on
sagittal images. he size of the thyroid gland changes with age;
Tables 48.1 and 48.2 list normal values. 85,86
Congenital Thyroid Lesions
Although some congenital thyroid lesions extend into both the
suprahyoid and the infrahyoid space, the pathology is described
here as it is inherent to the thyroid.
Because untreated hypothyroidism can result in severe mental
retardation and delayed bone development, there is a nationwide
program in the United States for neonatal screening. Congenital
hypothyroidism is present in 1 per 4000 infants and is twice as
common in girls as in boys. 87,88 Causes include agenesis, dysgenesis,
and goiter from inborn error of metabolism, maternal
thyrotoxicosis, or maternal ingestion of iodine, antithyroid
medication, or lithium. 29,87 About 85% of cases are caused by
dysgenesis (structural defects of the thyroid gland), either
TABLE 48.1 Normal Dimensions of the
Thyroid Gland a
No. of Subjects
(Male-to-Female
Ratio)
Thickness
(cm) b
Width
(cm) b
CORRECTED GESTATIONAL WEEKS
30-33 5 (4: 1) 0.8 ± 0.1 1.1 ± 0.3
33-37 19 (13: 6) 1.1 ± 0.3 c 1.4 ± 0.3 d
HEIGHT (cm)
45-50 42 (20: 22) 1.4 ± 0.2 c 1.7 ± 0.2 c
50-70 42 (27: 15) 1.4 ± 0.1 1.8 ± 0.2
70-90 8 (6: 2) 1.4 ± 0.1 1.9 ± 0.1
90-100 8 (3: 5) 1.4 ± 0.1 1.8 ± 0.2
100-110 34 (12: 22) 1.5 ± 0.3 2.1 ± 0.3
110-120 35 (20: 15) 1.7 ± 0.3 2.3 ± 0.3
120-130 45 (23: 22) 1.8 ± 0.4 2.4 ± 0.3
130-140 36 (21: 15) 1.9 ± 0.5 2.7 ± 0.2
140-150 42 (20: 22) 2.1 ± 0.4 2.8 ± 0.3
150-160 59 (25: 34) 2.2 ± 0.4 2.8 ± 0.4
160-170 16 (14: 2) 2.4 ± 0.4 3.0 ± 0.4
a As a function of corrected gestational weeks in premature neonates
and as a function of height from neonates to adolescence.
b Mean ±1 standard deviation.
c Compared with 30-33 weeks: p < .01.
d Compared with 30-33 weeks: p < .05.
With permission from Ueda D, Mitamura R, Suzuki N, Yano K, Okuno
A. Sonographic imaging of the thyroid gland in congenital
hypothyroidism. Pediatr Radiol. 1992;22(2):102-105. 86
hypoplasia or ectopia. 88 Sonography is the best imaging modality
in congenital hypothyroidism because it correctly deines presence
of the thyroid gland, which may be classiied as large, normal,
small, or absent. 89 Large glands are typically goitrous. Normalsized
glands in children with congenital hypothyroidism have
been observed in patients with pseudohypoparathyroidism,
trisomy 21, hypopituitarism, maternal antibody–induced