Discussion
The purpose of this case report is
to draw the attention of the obstetrical practitioner to the importance
of detailed transvaginal ultrasound examination including colour doppler
to prevent accidents caused by unusual vasa praevia rupture.
The guidelines of the International Society of Ultrasound and Gynecology
(ISUOG) for the second trimester examination mention the position of the
placenta [2]. If the lower placental edge reaches or overlaps the
internal os, a follow-up examination in the third trimester is
recommended. The guideline mentions that detailed examination for vasa
praevia may not need to be performed if the position and morphology of
the placenta are normal.
Prince reported a case of vasa praevia with anomalous umbilical cord
formation [3]. In this case, vasa praevia was not diagnosed
prenatally. Routine screening by transabdominal ultrasound in the second
and third trimester showed an anterior placenta not covering the
cervical os. Further examination for vasa praevia was not performed.
Fortunately, vaginal delivery was possible without serious complications
for the neonate. This case is similar to our case in having an
unexpected course of foetal vessels which resulted in vasa praevia. In
such cases, transvaginal ultrasound without colour doppler may not be
able to detect vasa praevia. The accuracy of transvaginal ultrasound in
the diagnosis of vasa praevia was previously reported to be high when
performed in combination with colour Doppler [4]. Initially,
obstetricians usually perform transvaginal ultrasound without colour
doppler. If the placenta and/or
umbilical cord vessels are not detected near the internal cervical os by
ultrasound without colour doppler, further examinations including colour
doppler may not be performed. In
our case, ultrasound with colour doppler was performed in order to
exclude for abnormal insertion of the umbilical cord before introduction
of a transcervical foley catheter for cervical ripening. A few foetal
vessels indicating vasa praevia were only detected after we performed
ultrasound with colour doppler, an incidental and fortunate diagnosis.
After diagnosis of vasa praevia, caesarean section before rupture of
foetal vessels is thought to be required for good prognosis of the
neonate. If foetal vessels are running on the anterior lower segment of
the uterus, obstetricians should be careful to avoid intraoperative
rupture of foetal vessels. Aoki et al. reported
a case of vasa praevia in which
the cord vessels were running on the anterior lower uterine segment
[5]. They made a horizontal incision on the uterine fundus to avoid
rupture of the cord. In future pregnancies after horizontal incision on
the uterine fundus, the risk of uterine rupture or placenta accreta are
higher relative to that of an incision in the lower uterine segment.
However, in their case they concluded that incision in the lower uterine
segment would have had a higher risk of rupture of cord vessels and loss
of massive foetal blood. We also predicted that the cord vessels were
running on the anterior lower uterine segment in our case. Both the
placental position and the site of umbilical cord insertion were above
the low transverse incision scar. A few foetal vessels were meandering
and running over the internal cervical os. We thought that safe delivery
via low transverse incision was feasible by putting the foetal vessels
at the lateral part of the incision scar. The precise diagnosis of vasa
praevia and assessment of the course of the cord vessels is essential
for a safe delivery. A change in the site of uterine incision may be
required. If the selected incision is not a normal low transverse
incision, an increased risk in future pregnancies should be considered.
Both the patient and her father had moyamoya disease. Although genetic
testing was not performed, familial disease was suspected. RNF213, the
gene related to angiogenesis and vascular inflammation was identified as
a susceptibility gene for moyamoya disease [6]. Recent research on
moyamoya disease has shown that RNF213 variants are associated not only
with moyamoya disease but also with intracranial atherosclerosis and
systemic vascular diseases, such as peripheral pulmonary artery stenosis
and renal artery stenosis [7]. Vasculopathy of umbilical and
placental vessels has not been reported. The main cause as to why vasa
praevia occurred in our case is not clear. However, a specific gene such
as RNF213 may be related to anomalous formation of umbilical cord
vessels which cause vasa praevia.