Diagnostic ultrasound ( PDFDrive )

1254 PART IV Obstetric and Fetal Sonography
Left
A
Right
B
C
Right
Left
D
FIG. 36.8 Congenital High Airway Obstruction Syndrome (CHAOS) at 19 Weeks. (A) Axial and (B) and coronal views of the chest show
diffusely enlarged, echogenic lungs bilaterally with eversion of the hemidiaphragms (arrows) and ascites (arrowhead). (C) and (D) Axial and coronal
T2-weighted MR images show increased lung volume and luid-illed airways (arrows). (Courtesy of Katherine Fong, MD, University of Toronto.)
he heart usually assumes a more central and anterior position
than normal and is oten compressed as the size of the lungs
increases. 110 Frequently, there are associated indings of ascites
and other signs of hydrops. he mechanism of ascites may be
from compression of the heart and great vessels by the enlarged
lungs. 120 Either polyhydramnios or oligohydramnios may be
present.
he lungs are distended and appear homogeneously echogenic
because of increased luid and increased lung growth induced
by the upper airway obstruction. 110 he increased number of
tissue-luid interfaces produces the hyperechoic appearance of
the lungs. Lung volume can increase up to 15 times the expected
size. he hyperplastic lungs are edematous but otherwise histologically
normal. 110
MRI can be used to identify the region of obstruction and
assist in decisions regarding in utero intervention and intrapartum
procedures. Characteristic indings include increased lung volume,
difuse increase in lung intensity on T2-weighted images, and a
dilated luid-illed trachea and bronchi. 116 Extrinsic causes of
tracheal compression can be evaluated. 118
More than 50% of fetuses with laryngeal obstruction have
associated abnormalities, most oten in the renal system and