NORMAL = 26

Imaging the
gravid CX :
HELPFUL
HINTS
Volume 18 Number 3 September 2001
ULTRASOUND
In Obstetrics & Gynecology
The Official Journal of
the International Society of Ultrasound
in Obstetrics and Gynecology
VOLUME 18
Faye C. Laing, M.D.
Department of Radiology
Division of Body Imaging
Georgetown Univ Hospital
Professor of Radiology
Georgetown Medical School
Washington, DC
Special theme:
Cervical Assessment and
Preterm Labor
LENGTH OF CERVIX - 24 WEEKS GA
Percentile:
10 25 50 75
NORMAL = 26-50 mm
DIGITAL EXAM
• Anatomic problems
• Subjective evaluation
• Risk of Infection
• Potential to rupture
membranes
LENGTH OF CERVIX
Iams et al. NEJM 1996;334,:569
CERVICAL LENGTH DETERMINATION*
30 Wks GA
N = 126
Mean
Digital US
EXAMINING THE CERVIX
Vaginal
• SONOGRAPHIC EVALUATION
18+6
41+10
50%(mm)
18
39
Transabdominal
25%(mm)
15
34
Translabial
10%(mm)
10
30
Transvaginal
*Anderson et al: Am J Obstet Gynecol 163:859;1990
1
TRANSABDOMINAL EXAMINATION
•
•
Most Common Method
Least Accurate
TRANSABDOMINAL LIMITATIONS
•
Bladder too full
•
Bladder too empty
•
Cervix obscured
TRANSABDOMINAL: LIMITATION
• Increases
measured
length of Cx
• False +
Placenta
Previa
Bladder too full
Is this cervix
normal ??
No!! It was
compressed by
overly distended
bladder.
TRANSABDOMINAL: LIMITATION
• Acoustic
shadowing
• Loss of
acoustic
window
Bladder too empty
Is this cervix
dilated ??
No!!
TL scan shows
normal cervix.
Empty bladder
was the problem.
2
Is there a way to
improve cervix
visualization using
a TA approach??
Cervix obscured with
curved transducer.
Problem resolved with
a sector transducer
TRANSABDOMINAL : KEY POINTS
•
Coned Down Cervical View
•
Look more than once
•
Bladder “relatively” empty
•
Patients history is important!!
•
Translabial / Transvaginal Scan
Is this a
dilated cervix
??
No!!
Cx is WNL on TL scan.
Cervix is obscured
in a pt with a resolving
LUS contraction.
TRANSLABIAL SCANNING
Mahony: In Nyberg et al.
Transvaginal Ultrasound. 171;1990
Rotate to a
sagittal scan
Start with a
coronal scan
3
TRANSLABIAL / TRANSVAGINAL US
•
CERV. EFFACEMENT/DILATATION
INDICATIONS
•
History preterm labor
Cervical effacement/dilatation
•
? cervical incompetence
Placenta previa
•
PROM
•
Post cerclage placement
T
Y
“T”
Trust Your Vaginal Ultrasound
V
HART,Z11
U
Zilianti et al. JUM 14:719,1995
Hx: 16 wks GA & Mild Cramping
“Y”
MARTINEZ Z38
4
“V”
“U”
CERVICAL LENGTH
1.5 cm = 50% effacement
1.0 cm = 75% effacement
Mahony et al. JUM 9:717, 1990
PROBABILTY of PRETERM DELIVERY
PRETERM BIRTH BEFORE 36 WEEKS*
CLINICAL
P
R
O
B
of
D
E
L
I
V
E
R
Y
30mm
CERVICAL LENGTH (mm)
Iams et al. NEJM 1996;334,:569
US
Dilatation Effacement Cerv
>2cm
>50%
<30mm
Sensitivity 62%
83%
100%
Specificity 39%
39%
45%
PPV
40%
48%
55%
NPV
61%
78%
100%
* Iams et al: Obstet Gynecol 84:40;1994
5
“HOURGLASS” CERVIX
“HOURGLASS” CERVIX
HANKINS, Z26
CX
VAGINA
Vagina
“HOURGLASS” CERVIX
IS THIS CERVIX NORMAL ??
RICHARD, Z11.
ANDERSON, Z 21
Z21 CHARLES, RT
No!!
Fundic pressure
decreases Cx length
by 15mm!!
Intact Membranes in Vagina
IS THIS CERVIX NORMAL ??
Johnson Z26.
IS THIS CERVIX NORMAL ??
+ COMPRESSION
No!!
In 2 minutes it’s length
spontaneously
decreased 34 mm!!
- COMPRESSION
No!!
It is being compressed
by the vaginal
transducer!!
6
IS THIS CERVIX NORMAL ??
FERREIRA Z19
It looks OK because
of a foot in the
endocervical canal !!
No!!
IS THIS CERVIX DILATED ??
PITFALLS : FALSE NEGATIVE
(LOOKS LONGER THAN IT IS)
•
Over distended bladder
•
Lack of fundic pressure
•
Intermittent dilatation
•
Vaginal probe compression
•
Fetal part in cervical canal
IS THIS CERVIX DILATED ??
MORALES, Z15
.
MORALES, Z15
No!!
A distended
bladder mimics a
dilated cervix.
SNEAKY SUBTLE CX DILATATION:COMPARE
VILLAR Z34
?
?
A vaginal cyst mimics a dilated cervix.
PITFALLS : FALSE POSITIVE
WHY IS THIS CERVIX SHORT ??
DILATED
It is obscured by rectal gas
PSEUDO-DILATED
Problem resolved: Use Vaginal Transducer
7
WHAT IS THE LENGTH OF THE CERVIX ??
• Mimics of endocervical fluid
Bladder
Paracervical fluid
Vaginal / Nabothian cyst
Lack of cervical mucous
DECAROLIS, Z12.
28mm
Linear measure
PITFALLS : FALSE POSITIVE
(LOOKS SHORTER THAN IT IS)
42mm
Curved measure
EVALUATING ? CERVICAL DILATATION
•
Transabdominal =
Poor
•
Translabial
=
Better
•
Transvaginal
=
Best
• Rectal gas (Translabial)
• Rectal gas (“ “ “ “ “ )
• Curved cervix
CERCLAGE
TRANSABDOMINAL CERCLAGE
COMPETENT
CERCLAGE
INCOMPETENT
CERCLAGE
8
DIAGNOSING PLACENTA PREVIA
• Sensitivity = 100%
• Specificity < 100% (False + relate to):
Technical Factors
Degree of previa
Gestational age
TROPHOTROPISM
• Responsible for “migration”
Proliferation of villi in region
of better endometrial blood
supply
•
Six Weeks Later
TROPHOTROPISM
Atrophy of villi in region of
poorer endometrial blood supply
•
VELAMENTOUS CORD in FRONT of CX
= VASA PREVIA
*
UMBILICAL CORD
Normal
FETAL
VESSELS
INTERNAL
OS
Velamentous
PLACENTA
Marginal
http://192.215.104.222/obgyn/cobra/cobra/TEXT/PROTOCOL/vasa2.htm
9
DIAGNOSING VASA PREVIA
Observe
normal PCIS
• Beware of migrating placenta
previa!!
• Color Doppler to look for PCIS
How can
Vasa Previa
be excluded
??
• Unsupported cord vessels (within
the membranes) crossing in front of
the cervix is diagnostic
Use Color to
Evaluate Cord
Velamentous Cord
Is this
Vasa Previa ??
Pulse Doppler
confirms
Vasa Previa
Vasa Previa
Pulse Doppler
Possibly----Is this
Vasa Previa ?? Note area in front of confirms
cx is now visible Vasa Previa
10
IMPORTANT DIGRESSION: Do you see a Previa?
YANG, Z36
NO!!
YES !!
“Coax” Presenting Part Away from CX
Could this be
Vasa Previa ??
Larger field of view
This is sneaky!! Nl
PCIS excludes VP!!
Dx was obligate cord
presentation
FALSE POSITIVE VASA PREVIA
Could this be
Vasa Previa ??
No!!
Venous flow is from
marginal vein.
•
Obligate cord presentation
•
Marginal vein
•
Cervical varices
EVALUATING ? PLACENTA PREVIA
•
Transabdominal
= Good
•
Translabial
= Best
•
Transvaginal
= Good
(not necessary)
11