Diagnostic ultrasound ( PDFDrive )

1136 PART IV Obstetric and Fetal Sonography
A B C
D
E
F
FIG. 33.3 Normal Neck. (A) Coronal sonogram of 21-week fetus showing pyriform sinuses, closed glottis, and subglottic trachea. (B) Coronal
view showing open glottis. (C) Axial view of the neck showing carotid and jugular vessels (arrowheads), trachea (long arrow), and vertebral body
(short arrow). (D) Axial view of neck shows thyroid (arrows). The carotids medially and the jugular veins laterally (open arrows) are posterior to the
thyroid. The trachea (T) is in the midline, and behind it a vertebral body with a small central developing ossiication center (O). The spinal cord (C)
is in the vertebral arch. (E) and (F) Magnetic resonance imaging coronal (E) and sagittal (F) views of normal glottis, vocal cords, and subglottic
trachea in a different, 27-week fetus.
causes such as underlying brain maldevelopment or injury or,
rarely, a space-occupying lesion. If the fetal head is suiciently
large, cephalopelvic disproportion can occur at delivery, leading
to failure of labor to progress and the need for cesarean
delivery.
Abnormal Shape
Abnormal head shape takes many forms. An abnormally long
and narrow (oblong) cranium is described as dolichocephaly
and is more frequently seen in fetuses in breech position and in
the setting of oligohydramnios. An abnormally round head is
termed brachycephaly, which may be caused by premature fusion
of the coronal sutures. A lemon-shaped skull, with indentation
of the frontal bones, is oten seen in association with open neural
tube defects and the Chiari II malformation of the hindbrain,
but it may also be seen in normal fetuses 18,19 (Fig. 33.4). A
strawberry-shaped skull—lattening of the occiput and narrowing
of the bifrontal portion of the cranium—may be seen in association
with trisomy 18. 20 A cloverleaf-shaped skull is seen with
some dwarfs, especially thanatophoric dysplasia, and in some
fetuses with craniosynostosis.
Craniosynostosis
Craniosynostosis describes a heterogeneous group of disorders
in which there is premature fusion of one or several of the cranial
sutures. Although abnormal head shape may be diagnosed in
utero, this diagnosis oten does not become evident until ater
birth. It occurs in about 1 per 2500 births. Recent research suggests
that the pathophysiology of craniosynostosis is related to abnormal
molecular signaling by ibroblast growth factors, 21-23 leading to