Diagnostic ultrasound ( PDFDrive )

CHAPTER 44 Cervical Ultrasound and Preterm Birth 1499
P
P
*
*
A
B
FIG. 44.6 Uterine Contractions. (A) TAS longitudinal image shows contraction (*) leading to a falsely elongated cervical canal (calipers), which
measures 7.4 cm. (B) After relaxation of the contraction, the cervix (calipers) measures 4.2 cm. P, Placenta.
60
*
*
Cervical length (mm)
50
40
30
20
10
99 th
97 th
95 th
90 th
75 th
50 th
25 th
10 th
5 th
3 rd
1 st
FIG. 44.7 Pseudodilation Caused by Uterine Contractions. Transabdominal
longitudinal scan shows a lower uterine segment contraction
(*) leading to a false appearance of dilated cervical canal. The closed
cervix (calipers) measures 3.5 cm.
0 1617181920212223 242526272829303132 33343536
Gestational age (weeks)
FIG. 44.8 Reference Ranges for Cervical Length Across Gestation.
First to 99th percentiles are indicated. (With permission from
Salomon LJ, Diaz-Garcia C, Bernard JP, Ville Y. Reference range for
cervical length throughout pregnancy: non-parametric LMS-based model
applied to a large sample. Ultrasound Obstet Gynecol. 2009;33[4]:
459-464. 33 )
is caused by a lower uterine segment contraction with partial
(Fig. 44.7) or complete approximation of the anterior and posterior
myometrium with the resultant false appearance of a “funnel”
above the closed cervix. he classic tips to recognize this appearance
is the artiicially elongated length of the cervix (>5 cm),
the normal cervix lying caudal with respect to the pseudodilation,
and the transient nature of this appearance.
Normal Cervix
Sonographically, the cervix appears as a distinct, sot tissue
structure containing midrange echoes. he endocervical canal
oten appears as an echogenic line surrounded by a hypoechoic
zone attributed to the endocervical glands (see Fig. 44.4B).
Occasionally, the endocervical canal may appear hypoechoic and
minimally dilated along its entire length. Benign nabothian cysts
can be seen within the cervical sot tissues.
Numerous studies have evaluated cervical length in normal
pregnancy. he typical cervix increases its length in the irst
trimester because of elaboration of the glandular content of the
cervix. 27 Salomon et al. 33 published a reference curve of cervical
length through gestation using TVS based on a large sample
(Fig. 44.8). Based on this study, at about 20 weeks’ gestation,