Diagnostic ultrasound ( PDFDrive )

1244 PART IV Obstetric and Fetal Sonography
Normal Sonographic Features of
the Fetal Chest
he fetal lungs are identiied by ultrasound as homogeneously
echogenic tissue surrounding the heart, separated by the
hypoechoic, dome-shaped diaphragm from the abdominal organs
(Fig. 36.1A and B). he fetal ribs are highly echogenic, curved
bony structures arising near the spine and extending anteriorly
to encompass more than half the thoracic circumference. Lung
echogenicity varies during gestation, in general increasing in
echogenicity as lung development progresses.
Assessment of lung volume is important for evaluation of
fetuses at risk for pulmonary hypoplasia, particularly in cases
of congenital diaphragmatic hernia (CDH), pleural efusions,
prolonged oligohydramnios, and skeletal deformities. Methods
to assess pulmonary size include measurement of the thoracic
circumference, 3 lung area (deined as internal thoracic area minus
cardiac area in diastole on a transverse four-chamber view 4 ),
and three-dimensional lung volumetry with ultrasound or
MRI. 5-7
he fetal lungs, thorax, and heart grow at similar rates, such
that the normal cardiothoracic ratio remains constant in the
Li
Lu
Li
Lu
A
B
Right
Left
C
Left
D E Right
F
G H I
FIG. 36.1 Normal Fetal Chest. (A) Sagittal view of torso at 13 weeks. Note liver (Li), lungs (Lu), and diaphragm (arrow). (B) Four-chamber
view of the heart surrounded by the homogeneous echogenic lungs at 18 weeks. (C) Coronal and (D) sagittal views of chest at 18 weeks show
the dome-shaped hemidiaphragms (arrow) separating the lungs (Lu) from intraabdominal organs and the relative hypoechoic appearance of the
liver (Li). (E) and (F) Axial and sagittal views of fetal chest (arrow) at 37 weeks. (G) Normal appearance of fetal thymus (arrowheads) at 37 weeks’
gestation. (H) Coronal T2-weighted MRI shows normal lungs and diaphragm at 37 weeks. (I) Axial T2-weighted MRI of thymus (arrows) anterior
to heart. The thymus is relatively hypoechoic to the surrounding lungs on ultrasound and intermediate signal on MRI.