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Diagnosis of Vasa Previa with Endovaginal Color Doppler and

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Diagnosis of Vasa Previa with Endovaginal Color Doppler and Powered By Docstoc
					                    Diagnosis of Vasa Previa with
                   Endovaginal Color Doppler and
                    Power Doppler Sonography:
                                           Report of Two Cases

                 Eric E. Sauerbrei, MD, FRCPC, Gregory L. Davies, MD, FRCSC, FSOGC




Vasa previa is a rare anomaly of chorionic develop-                existed at this time. Subsequent transabdominal sono-
ment in which unprotected umbilical arteries and                   grams (without color Doppler sonography) were obtained
veins traverse the lower uterine segment at or near                at 18, 23, 26, 28, and 31 weeks’ gestation. The patient
the internal cervical os, ahead of the presenting fetal            reported vaginal bleeding before each of these except at 28
part. Vasa previa is associated with one of the fol-               weeks. At 23 weeks’ gestation, the umbilical cord was per-
                                                                   sistently positioned between the presenting fetal part and
lowing: velamentous cord insertion, marginal cord
                                                                   the cervix (i.e., funic cord presentation). The internal cervi-
insertion, or bilobed placenta (e.g., succenturiate pla-           cal os was clear of placenta, but two short linear echoes
cental lobe). Perinatal mortality is high owing to ves-            were noted nearby (Fig. 1). The significance of these was
sel rupture after spontaneous or iatrogenic rupture of             not appreciated at the time.
membranes. Diagnosis prior to the onset of labor                      At 36 weeks’ gestation, a transvaginal sonogram with
could prevent fetal morbidity and mortality. We                    color Doppler and power Doppler sonography defini-
report two cases in which the diagnosis was made                   tively diagnosed vasa previa (Fig. 1). The spectral
antepartum with endovaginal color Doppler and                      Doppler findings confirmed the fetal cardiac rate in the
power Doppler sonography.                                          artery that covered the internal cervical os. The patient
                                                                   was delivered by elective cesarean section on the basis of
                                                                   these findings and the continued vaginal bleeding.
                                                                      Vasa previa was confirmed at cesarean section. The pla-
                           CASE 1
                                                                   centa had a velamentous cord insertion with blood ves-
                                                                   sels noted within the membranes. The male infant
The patient was referred initially for a dating sonogram at        weighed 2355 g and the Apgar scores were 9 at 1 min and
13 weeks 3 days of gestation, at which time the placenta           9 at 5 min.
was anterior and low. No history of vaginal bleeding

                                                                                              CASE 2

                                                                   The patient was referred initially with vaginal bleeding at
  Received December 2, 1997, from Imaging Services, Kingston       19 weeks’ gestation. The transabdominal sonogram
General Hospital, Kingston, Ontario. Revised manuscript accepted   demonstrated a low placenta and possibly marginal pla-
for publication February 20, 1998.
  Address correspondence and reprint requests to Eric Sauerbrei,   cental veins at the internal cervical os. Transabdominal
MD, c/o Imaging Services, Kingston General Hospital, 76 Stuart     sonograms at 21 and 23 weeks’ gestation also suggested a
Street, Kingston, ON K7L 2V7, Canada.                              marginal placenta previa.

 1998 by the American Institute of Ultrasound in Medicine • J Ultrasound Med 17:393–398, 1998 • 0278-4297/98/$3.50
394      VASA PREVIA                                                                      J Ultrasound Med 17:393–398, 1998




   At 25 weeks’ gestation, the transabdominal sonogram                 Vasa previa can be lethal if undiagnosed. The
with power and spectral Doppler interrogation suggested             perinatal mortality is over 50%2 because of the risk
vasa previa (Fig. 2). At 28 weeks’ gestation, the endovagi-         of rupture of the unprotected fetal blood vessels
nal color Doppler sonogram confirmed the presence of                and subsequent fetal exsanguination. However, the
vasa previa (Fig. 2).                                               condition is uncommon (approximately 1 in 3000
   Elective cesarean section was performed at 33 weeks’
                                                                    to 1 in 5000 pregnancies),2,3 and thus it not always
gestational age. The fetus was female (1956 g) with Apgar
scores of 4 at 1 min and 6 at 5 min. Inspection of the pla-         considered.
centa and membranes revealed three or four medium                      Conventional obstetrical sonography is not effec-
sized vessels traversing the membranes. Sections of the             tive in diagnosing vasa previa or its most common
placenta show thinned areas with intervillous fibrin depo-          predisposing condition, velamentous cord insertion.
sition, consistent with placenta membranacea.                       Heinonen and coworkers4 performed sonography on
                                                                    80 patients with velamentous cord insertion but
                                                                    detected only one case prenatally. Eddleman and col-
                        DISCUSSION                                  leagues3 reviewed 82 cases of velamentous cord
                                                                    insertion, of which three were complicated by vasa
Vasa previa implies that unprotected umbilical arter-               previa. Routine nontargeted obstetrical ultrasonog-
ies and veins traverse the lower uterine segment at or              raphy failed to detect any cases of velamentous cord
near the internal cervical os. This may occur in vela-              insertion, including the three cases of vasa previa.
mentous insertion or marginal insertion of the umbil-               The rate of velamentous cord insertion in this series
ical cord into the placenta or in a bilobed placenta or             was 1 in 200 and the prevalence of vasa previa was
succenturiate placental lobe. Velamentous cord inser-               1 in 5467. Raga and coauthors1 demonstrated in a
tion is more common in multifetal pregnancies.1                     report of two twin pregnancies that transabdominal

Figure 1 Case 1. A, Sagittal transabdominal sonogram,               A
23 weeks’ gestation. The umbilical cord (U) was persistently
positioned between the fetus and the cervix (i.e., funic cord
presentation). The significance of the two short linear echoes
(short arrows) was not appreciated at the time of the sonogram.
Shortest arrows indicate cervical canal. B, Sagittal endovagi-
nal sonogram with color Doppler sonography, 36 weeks’ ges-
tation. A blood vessel (V) is observed at the position of the
internal cervical os. U, Umbilical cord positioned between the
internal cervical os and the fetus (F). Small arrows indicate
position of cervical canal. C, Sagittal endovaginal sonogram
with spectral Doppler interrogation, 36 weeks’ gestation. The
Doppler cursor is placed in the blood vessel at the internal cer-
vical os. The spectral Doppler graph demonstrates fetal arter-
ial blood flow with a rate of 137 beats per minute. The mater-
nal heart rate was 86 beats per minute (the time interval
between successive marks at the bottom of the graph is 0.2 s).
B                                                                   C
J Ultrasound Med 17:393–398, 1998                                                                   SAUERBREI AND DAVIES                 395




Figure 2 Case 2. A, Sagittal transabdominal sonogram, 25 weeks’ gestation. Midline scan depicts the cervix and the internal cervical
os (arrow). No soft tissue is noted overlying the internal cervical os. B, Sagittal transabdominal sonogram with power Doppler inter-
rogation, 25 weeks’ gestation. Same scan plane as in A. Power Doppler sonography demonstrates flow in a blood vessel (a) at the posi-
tion of the internal cervical os along the inner aspect of the uterus. The blood vessel immediately caudal to this blood vessel (a) is locat-
ed inside the myometrium. C, Sagittal transabdominal sonogram with spectral Doppler interrogation, 25 weeks’ gestation. The
Doppler cursor is placed in the blood vessel at the position of the internal cervical os (a in B). The spectral Doppler graph (at the bot-
tom of image) demonstrates fetal arterial blood flow with a rate of 150 beats per minute. The Doppler analysis of the blood vessel
inside the myometrium demonstrated the maternal heart rate of 78 beats per minute (the time interval between successive marks at
the base of the graph is 0.2 s). D, Sagittal endovaginal sonogram with color Doppler interrogation, 28 weeks’ gestation. Color Doppler
sonography demonstrates a blood vessel (large arrows) coursing along the uterine wall to the level of the internal cervical os. Note the
path of the cervical canal (small arrows). E, Sagittal endovaginal sonogram with spectral Doppler interrogation, 28 weeks’ gestation.
The Doppler cursor is placed in the blood vessel at the internal cervical os. The spectral Doppler graph demonstrates fetal arterial
blood flow with a rate of 150 beats per minute (the time interval between successive marks along the bottom of the graph is 0.2 s).




A                                                                        B




C                                                                        D




E
396       VASA PREVIA                                                                        J Ultrasound Med 17:393–398, 1998




color Doppler sonography can be useful in detect-                      In six of seven case reports (Table 1), postpartum
ing velamentous cord insertion. Vasa previa was                      examination of the placenta and membranes
not present in these two pregnancies.                                demonstrated several blood vessels overlying the
  A review of the English literature revealed four                   internal os of the cervix, and in one of seven cases,
case reports in which transabdominal color                           a single large-bore vessel constituted the vasa pre-
Doppler sonography was used to diagnose or                           via. In our two reported cases, postpartum exami-
confirm the presence of vasa previa.5–8 In two other                 nation revealed several aberrant vessels within the
case reports, transvaginal color Doppler sono-                       membranes. The two patients reported here were
graphy was used to diagnose vasa previa,9,10 and in                  diagnosed because vaginal sonography with color
another case,11 transvaginal sonography confirmed                    Doppler interrogation was used to define exactly
the presence of vasa previa after digital vaginal                    the relationship of the placental margin, the internal
examination detected the fetal artery at the internal                cervical os, and the vessels at the margins of the pla-
cervical os.                                                         centa. In our practice, if the placenta is low but the
  In these seven case reports (Table 1), three                       fetal presenting part obscures the placental margin
patients had vaginal bleeding and four patients had                  and internal cervical os, we gently displace the pre-
no vaginal bleeding. The diagnosis was made                          senting fetal part out of the lower uterine segment
between 24 weeks 4 days and 39 weeks’ gestation                      while scanning through the bladder in the midline
(mean of 30 weeks). In three of seven cases the pre-                 sagittal plane. We also utilize color Doppler sonog-
disposing anomaly was a bilobed placenta or suc-                     raphy to assess the marginal blood vessels (mar-
centuriate lobe, in three other cases velamentous or                 ginal placental veins) in relation to the internal
marginal cord insertion, and in the seventh a suc-                   cervical os. If there is any question at that point, we
centuriate lobe and velamentous cord insertion. In                   consider a transvaginal sonogram to allow better
our two reported cases the predisposing anomalies                    definition of the anatomy. We perform this
were velamentous insertion and placenta mem-                         procedure only in consultation with the referring
branacea.                                                            obstetrician in whose opinion it is safe to proceed.


Table 1: Case Reports of Vasa Previa (English Literature)
                                   Vaginal Bleeding   Gestational
                        Number         as Initial       Age (wk)        TAS +     TVS +                         Number
Reference               of Cases     Presentation     at Diagnosis      CDU       CDU       Pathology           of Vessels

Harding et al5 (1990)      1             Yes            24 wk 4 d         1                 Succenturiate       One large-
                                                                                            lobe                bore vessel
Nelson et al6 (1990)       1             No                26             1                 Velamentous         Four major
                                                                                            cord insertion      vessels
Hsieh et al7 (1991)        1             No                30             1                 Succenturiate       Many fetal vessels
                                                                                            lobe
Arts et al11 (1993)        1             Yes               39                       1*      Succenturiate       Several vessels
                                                                                            lobe; velamentous
                                                                                            cord insertion
Meyer et al9 (1993)        1             No                27             1          1      Marginal            Large vein and
                                                                                            cord insertion      small artery
Hata et al10 (1994)        1             No                30             1          1      Velamentous         Vessels extending
                                                                                            cord insertion      across the
                                                                                                                internal os
Fleming et al8 (1996)      1             Yes            32 wk 2 d         1                 Bilobed             Several vessels
                                                                                            placenta
Sauerbrei and Davies       2             No                36             1          1      Velamentous         Several vessels
                                                                                            cord insertion
                                         Yes               28             1          1      Placenta            Several vessels
                                                                                            membranacea

*Blood vessels first palpated at digital vaginal examination. Sonography then used to confirm finding.
TAS, Transabdominal sonogram; TVS, transvaginal sonogram; CDU, Color Doppler ultrasonography.
J Ultrasound Med 17:393–398, 1998                                                      SAUERBREI AND DAVIES              397




   With the patient’s hips and knees flexed and the                   presenting fetal part may be gently displaced
pelvis elevated with pads, the vaginal probe is                       from the lower uterine segment to allow opti-
inserted while observing the structures in front of the               mal visualization.
cervix (i.e., vagina, urethra, bladder base). We thus            3.   If the umbilical cord persistently occupies the
see the relationship of the probe surface and cervical                lower uterine segment in front of the present-
canal at all times. The probe eventually comes to rest                ing fetal part (funic cord presentation), color
against the anterior aspect of the cervical body. At                  Doppler sonography may be useful in detect-
this point, a midline sagittal sonogram outlines the                  ing the exact site of the cord insertion and its
cervical canal, the internal cervical os, the edge of the             relation to the internal cervical os.
placental tissue, and the marginal placental veins.              4.   If conventional sonography demonstrates a
Color Doppler sonography with or without power                        ridge or linear echo or membrane near the
Doppler sonography enhances visualization of the                      cervix, color Doppler sonography should be
marginal veins. If placental tissue or marginal veins                 used to assess for blood vessels in this area.
cover the internal cervical os or abut on the edge of            5.   If sequential sonograms have demonstrated
the os, these are considered to be clinically significant             “migration” of the placenta away from the
(i.e., placenta previa or marginal placenta previa,                   cervix, color Doppler sonography should be
respectively). If we cannot visualize these structures                used to assess for blood vessels near the cervix.
satisfactorily, we will gently displace the presenting           6.   In a multifetal pregnancy, the prevalence of
fetal part out of the lower uterine segment to allow                  velamentous cord insertion is increased and
optimal visualization. In these ways optimal visual-                  color Doppler sonography may be employed
ization can be obtained in virtually every instance.                  to establish the sites of insertion of the umbil-
Using these strategies in our two patients, we                        ical blood vessels.
detected arteries covering the internal cervical os.           We find that transvaginal color Doppler is signifi-
The spectral Doppler sonogram confirmed that these          cantly more sensitive than transabdominal color
were fetal arteries with heart rates of approximately       Doppler sonography in detecting blood flow in blood
150 beats per minute. Similarly, the images con-            vessels near the cervix. The reasons for this include
firmed that these were fixed at the os and not free         the shorter distance between probe and blood vessels,
within the amniotic fluid.                                  the lack of intervening sound-scattering media (such
   Power Doppler sonography is more sensitive than          as maternal abdominal wall, uterine wall, placenta,
conventional color Doppler ultrasonography for              and fetal structures), and the intrinsic superior sensi-
nonpulsatile low flow in veins and thus is useful to        tivity of Doppler interrogation with the vaginal
assess for marginal placental veins and fetal veins.        probe. Because it is easy to miss vasa previa with opti-
However, good quality color Doppler sonography is           mized transabdominal color Doppler sonography, we
excellent in depicting the pulsatile blood flow in fetal    would proceed to transvaginal sonography in high
arteries, including those in vasa previa.                   risk (i.e., high risk for vasa previa) circumstances if
   When should color Doppler or power Doppler               this is safe and feasible clinically.
sonography be used to assess for possible
velamentous cord insertion or vasa previa? The
following constitute the most common high-risk                                      REFERENCES
circumstances:
  1. If the patient has a bilobed placenta or succen-
                                                            1.    Raga F, Ballester MJ, Osborne NG, et al: Role of color flow
     turiate placental lobe, transabdominal color                 Doppler ultrasonography in diagnosing velamentous
     Doppler or power Doppler sonography                          insertion of the umbilical cord and vasa previa: A report
     should be used to search for intramembra-                    of two cases. J Reprod Med 40:804, 1995
     nous fetal blood vessels connecting the two            2.    Young M, Yule N, Barham K: The role of light and sound
     placental bodies.                                            technologies in the detection of vasa praevia. Reprod
  2. If the cord insertion into the central portion of            Fertil Dev 3:439, 1991
     the placenta is not visible with conventional          3.    Eddleman KA, Lockwood CJ, Berkowitz GS, et al:
     sonography, color Doppler sonography may                     Clinical significance and sonographic diagnosis of vela-
     be used to assess for eccentric cord insertion or            mentous umbilical cord insertion. Am J Perinatol 9:123,
                                                                  1992
     velamentous cord insertion. If the detected
     cord is in the lower uterine segment, its rela-        4.    Heinonen S, Ryynanen M, Kirkinen P, et al: Perinatal
                                                                  diagnostic evaluation of velamentous umbilical cord
     tionship with the cervix must be defined. If                 insertion: Clinical, Doppler, and ultrasonic findings.
     the persisting fetal part obscures this area, the            Obstet Gynecol 87:112, 1996
398       VASA PREVIA                                                                       J Ultrasound Med 17:393–398, 1998




5.    Harding JA, Lewis DF, Major CA, et al: Color flow            9.   Meyer WJ, Blumenthal L, Cadkin A, et al: Vasa previa:
      Doppler—-A useful instrument in the diagnosis of vasa             Prenatal diagnosis with transvaginal color Doppler flow
      previa. Am J Obstet Gynecol 163:1566, 1990                        imaging. Am J Obstet Gynecol 169:1627, 1993
6.    Nelson LH, Malone PJ, King M: Diagnosis of vasa previa       10. Hata K, Hata T, Fujiwaki R, et al: An accurate antenatal
      with transvaginal and color flow Doppler ultrasound.             diagnosis of vasa previa with transvaginal color Doppler
      Obstet Gynecol 76:506, 1990                                      ultrasonography. Am J Obstet Gynecol 171:265, 1994
7.    Hseih F-J, Chen H-F, Ko T-M, et al: Antenatal diagnosis of   11. Arts H, van Eyck: Antenatal diagnosis of vasa previa by
      vasa previa by color flow mapping. J Ultrasound Med              transvaginal color Doppler sonography. Ultrasound
      10:397, 1991                                                     Obstet Gynecol 3:276, 1993
8.    Fleming AD, Johnson C, Targy M, et al: Diagnosis of vasa
      previa with ultrasound and color flow Doppler: A case
      report. Nebraska Med J 81:191, 1996

				
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