Diagnostic ultrasound ( PDFDrive )

1652 PART V Pediatric Sonography
A
B
FIG. 48.40 Type II Branchial Cyst. (A) Transverse side-by-side image of the right and left sides of the neck. There is a unilocular, anechoic,
encapsulated cystic lesion with through transmission in the left neck medial to the left sternocleidomastoid muscle. (B) Coronal computed tomography
scan demonstrates the elliptical cyst (arrow) medial to the sternocleidomastoid muscle and lateral to the pharynx, type III of the second branchial
apparatus anomalies.
FIG. 48.41 Type III Branchial Apparatus Cyst. There is a unilocular
complex hypoechoic cyst in the lower neck adjacent to the thyroid
cartilage, suggesting hemorrhage or infection. No low was present on
color Doppler.
Ectopic Thymus
he thymus gland arises in the sixth week of gestation as outpouchings
of primarily the third and a small portion of the
fourth pharyngeal pouches. 93 Caudal elongation leads to the
formation of tubular structures known as the thymopharyngeal
ducts. By the ninth week, migration due to attachment to the
pericardium is followed by obliteration of the duct from the
angle of the mandible, along the carotid sheath, to the level of
the superior mediastinum. he resulting migrating solid masses
fuse to form thymus tissue anatomically located below the thyroid
gland. 150 Superior cervical extension of the thymus is normal in
children and young adults, seen in nearly 66% of these patients
anywhere along the course of descent. 146,150,151 he ectopic thymus
can be diferentiated from other masses via sonography because
of isoechogenicity and sometimes continuity with normal thymus,
sharp angulated margins, parallel septa, pliability, lack of mass
efect, and absence of central hilum with color Doppler imaging 43,150
(Fig. 48.43).
With persistence of the thymopharyngeal duct or progressive
cystic degeneration of the thymic tissue, a thymic cyst may
occur. 99,130 Most thymic cysts occur in the irst decade of life,
with a male and let-sided predominance. 152 Approximately 50%
of cervical cysts are in continuity with a mediastinal mass. 43,153
On ultrasound, the lesions are typically large, unilocular or
multilocular cysts intimately associated with the carotid space,
oten splaying the carotid artery and jugular vein 144,153 (Fig. 48.44).
Intralesional debris can occur in the presence of hemorrhage or
infection. 101 here are no reports of associated neoplasm, but
surgical resection is the treatment of choice. 93,152
Dermoid and Epidermoid Lesions
Dermoid and epidermoid lesions represent 7% of head and neck
lesions and 25% of midline cervical anomalies. 93,98 hese lesions
develop when there is inclusion of ectodermal tissue during the
fusion of the branchial arches. 146,154 Dermoid cysts contain two
germ layers, both ectoderm and mesoderm, whereas epidermoid
cysts consist of only one germ layer, ectoderm. 99,140 Although
the majority of these masses are found around the orbit or adjacent
to the nose, approximately 11% of these cysts occur in the loor
of the mouth in the submandibular space. 93 With regard to imaging
of the neck, most occur as a painless, slow-growing midline neck
mass in the loor of the mouth, or less oten in the thyroidal or
suprasternal area. 43 Ultrasound of these lesions mimics a “pseudosolid”
appearance, demonstrating a well-circumscribed,
thin-walled unilocular mass with internal echoes and minimal
posterior echo enhancement 152 (Fig. 48.45). Sometimes, there
may be mixed echoes owing to internal fat or posterior shadowing
in the presence of calciication. 152 Surgical resection is