Diagnostic ultrasound ( PDFDrive )

CHAPTER 50 The Pediatric Chest 1723
AV
Inverted
A B C
FIG. 50.34 Paget-Schroetter Syndrome. (A) Gray-scale, (B) color low, and (C) spectral Doppler waveform images show subclavian vein
thrombosis with absence of color low and absence of Doppler signal secondary to a thoracic outlet syndrome in a 17-year-old female equestrian.
(Courtesy of Dr. Charles A. James, Arkansas Children’s Hospital, Little Rock, AK.)
Lymphovascular Malformation
Lymphatic malformations 51 (Fig. 50.35) are composed of dilated
lymphatic sacs of variable size, which may appear unilocular or
multilocular. Lymphatic malformations may undergo hemorrhage,
in which case the lesion appears as a uniformly echogenic mass
or multiple cysts containing echogenic debris. Septations in cystic
lesions are better identiied by ultrasound than by CT or magnetic
resonance imaging (MRI).
MEDIASTINAL MASSES
CT and MRI are the primary modalities for evaluation of
mediastinal masses detected by chest radiography. Suprasternal
sonography 52 can be useful for detecting small and large mediastinal
masses, particularly lymphoma. Mediastinal sonography
for masses should include major vessels or cardiac chambers in
the ield of view so that mass and vessel echogenicity can be
compared directly. his prevents the pitfall created by reducing
the gain setting in response to the hyperechoic appearance of
adjacent lung. he reduced gain setting gives a falsely anechoic
appearance to a solid mass. Juxtaphrenic paravertebral masses
may be detected with a subxiphoid or transdiaphragmatic
approach.
Mediastinal ultrasound can also determine whether chest
masses extend into the neck. Retrosternal thyroid mass extension
detection by ultrasound is helpful for surgical planning. Ultrasound
allows characterization of masses as solid or cystic. Doppler
imaging may be helpful in evaluating whether a chest mass is
vascular in origin. Malignant chest masses demonstrate a lowimpedance,
high–diastolic-low Doppler signal. 53 Color Doppler
ultrasound before percutaneous biopsy can rule out vascular
lesions that would preclude biopsy.
A widened superior mediastinum detected on chest radiography
can be evaluated initially by sonography. Detection of a
normal but prominent thymus rather than a mediastinal mass
precludes the need for CT. he thymus is normally located in
the superior mediastinum anterior to the great vessels in the
superior mediastinum, from the superior edge of the manubrium
to the fourth costal cartilage. he thymus is mildly hypoechoic
relative to liver, spleen, and thyroid. It shows some echogenic
strands. A ine granular echotexture gives the thymus a “starry
sky” appearance (see Fig. 50.31). A ibrous capsule gives the
thymus a smooth, well-deined margin.
Thymic Index
hymic index is the product of thymic width measured on
transverse images and the area of the largest lobe measured on
a longitudinal image 54-56 (Table 50.1). he thymic index has
acceptable correlation with actual thymus weight and volume.
he measurement is performed during expiration to obtain a
standardized size. hymic index is greater in children with active
atopic dermatitis than in healthy controls 57 (Fig. 50.36). Larger
thymic index at birth is associated with lower infant mortality
rate. 58 hymic size varies with age, and normal thymic index
values have been established 54-56 (Table 50.2).
Abnormal Location of Thymus Mimicking
Mass Lesion
Superior herniation of thymus into the neck is a rare entity in
which there is intermittent migration of the broadest part of the
normal thymus out of the thorax into the suprasternal region.
Real-time ultrasound shows that the mass moves into the neck
during Valsalva maneuver, with an increase in the intrathoracic
pressure, and has typical echotexture of thymus, thereby avoiding
unnecessary biopsy and surgery. 59 Cervical ectopic thymus is
an uncommon variant. A hypoechoic mass with characteristic
thymic ultrasound echotexture is identiied along the track of
the thymopharyngeal duct. 60,61 he thymus can protrude into
the chest wall as a bulging mass because of a congenital sternal
defect. Real-time ultrasound can demonstrate movement of
herniated thymus during respiratory cycles.
Anterior Mediastinal Masses
Benign abnormalities of the thymus in children include thymic
cyst, intrathymic hemorrhage, thymolipoma, and thymoma. he
thymus may also be involved by a hemangioma, lymphatic