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\begin{document}

\title{Vasa previa or not? A special parachute type of placenta caused dispute
in ultrasonography diagnosis: A case report.}



\author[1]{Ling Hong}%
\author[1]{Jiahan Wu}%
\affil[1]{Ningbo Women and Children's Hospital}%


\vspace{-1em}



  
  \date{May 26, 2024}


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\textbf{Vasa previa or not? A special parachute type of placenta caused
dispute in ultrasonography diagnosis: A case report.}

Hong Ling\textsuperscript{1}, Wu Jiahan\textsuperscript{1}.

1 Department of Obstetrics and Gynecology, Ningbo Women and Children
Hospital, Ningbo 315010, China

Corresponding Author

Wu Jiahan

No. 339 Liuting Street, Haishu District, Ningbo, Zhejiang Province,
China.

Telephone number +86 13805840722~ e-mail 3014078594@qq.com

Co-author

Hong Ling

No. 339 Liuting Street, Haishu District, Ningbo, Zhejiang Province,
China.

Telephone number +86 13655742069~ e-mail 409180445@qq.com

\textbf{shortened running title:} Vasa previa or not? MRI for parachute
placenta

\textbf{Abstract}

We present here a case of vasa previa with a special parachute placenta.
During two times of ultrasonic scanning, there was dispute for the
existence of vasa previa. Then the patient was referred to magnetic
resonance imaging(MRI) scanning, and a parachute type of placenta and a
previa vessel were identified. The patient subsequently underwent an
elective cesarean section after 34 weeks of gestation, giving birth to a
healthy child with an uneventful post-partum course. The cesarean
section avoided laceration of the vasa previa which would probably bring
fetal life threatening complication due to acute fetal blood loss. The
identification and exclusion of vasa previa are essential to ensure
appropriate and timely treatment. If there's contradictory
ultrasonography results, MRI may offer some assistance in diagnosis.

\textbf{Key words}

vasa previa, parachute type of placenta, magnetic resonance imaging(MRI)

\textbf{Introduction}

Vasa previa is defined as placental vessels supported only by membranes,
overlie the cervix, lie between the cervix and the presenting fetal
part\textsuperscript{{[}1{]}}. The prevalence of vasa previa is
approximately 1 in 2500, but much higher among patients with low lying
placenta, in vitro fertilization(IVF), or abnormal placental morphology,
such as bipartite or succenturiate lobe placentas in the lower uterine
segment\textsuperscript{{[}2{]}}. These previa vessels are vulnerable
not only to compression, which may lead to fetal anoxia, but also to
laceration, which can lead to acute fetal blood loss or
exsanguination\textsuperscript{{[}3{]}}. That results in poor pregnancy
outcomes if not diagnosed prenatally\textsuperscript{{[}4{]}}.

\textbf{Case}

Our case was a 36-year-old Asian women, gravida 2 para 0. Before 32
weeks of gestation, the patient had gone to the local clinical institute
as scheduled for prenatal examinations. Everything went smoothly during
her process of pregnancy by then. At 33 weeks of gestation, the patient
was found low lying placenta in that local institute by ultrasonography,
and was referred to our hospital, a municipal tertiary institute.

An ultrasonography Specialty Register gave the transabdominal ultrasonic
scan initially, and described as follows, ``The placenta locates at the
anterior wall of the uterine cavity, the distance between the placenta
lower margin to the cervical internal os is 18mm. The insertion site of
the umbilical cord is at the posterior wall of the uterine cavity,
several vessels supported only by membranes insert into the placenta
edges, including one vessel goes along the interior surface of the
uterine fundus entering the placenta upper pole, and another vessel goes
along the lower uterine segment entering the placenta lower pole near
the cervix''(Figure.1 \textbf{a} ). Though a little puzzled as the
insertion site of the umbilical cord and the placenta location were at
posterior and anterior walls respectively, the diagnosis was obviously
vasa previa. According to the guidelines, we should accomplish the
cesarean section at 34 to 35 weeks\textsuperscript{{[}5{]}}.

However, the patient insisted on obstetricians' reconsidering
possibility of vaginal delivery since the vessel entering the placenta
lower pole didn't go exactly over the cervical internal os. 3 days
later, we offer second time of ultrasonic examination. This time, an
ultrasonography Consultant gave both transabdominal scan and
transvaginal gray scale with color Doppler, and described as follows,
``Yes, the umbilical cord insertion is at posterior wall and the
placenta locates at the anterior wall. But no obvious sign of vessel
overlying the cervix''. That result might overturn the previous
diagnosis of vasa previa. So should we still schedule the cesarean
section at 34 weeks of gestation?

In order to further understand the relationship between the patient's
umbilical cord and placenta, we referred her to MRI scan. The
radiologists didn't give any confirmation about umbilical vessels,
because they're usually specialists focusing on diagnosis of placenta
increta, since vasa previa identification is commonly in sonographers'
field. But our obstetricians found a isolated vessel supported only by
membrane going along the lower uterine segment and entering placenta
lower pole near the cervix, just as the ultrasonography Specialty
Register had described(Figure.1 \textbf{b} and \textbf{c} ). The
umbilical cord truly inserted at posterior wall of the uterine cavity,
and Wharton's jelly lost from there with a great number of isolated
vessels traveling through membranes connected to the anterior wall
placenta(Figure.1 \textbf{c} and \textbf{d} ).

At first, we considered there might be a very tiny placenta at the
posterior wall and then connected by naked vessels to the much larger
succenturiate lobe at the anterior wall. Immediately, an obstetric
Specialty Register pointed out there was hardly any space for placental
tissue existing between the amnion and the uterine muscle at posterior
wall. Ultimately, we got the conception that it was a special
``parachute'' type of placenta, with no placental tissue at the
posterior wall, just several isolated vessels diverging from umbilical
posterior wall insertion site, like strings connecting to the parachute
canopy, to the anterior wall placenta.

We performed a cesarean section at 34 weeks and 3 days of gestation. At
the time of surgery, the incision at lower uterine segment was gradually
and carefully deepened until the decidua reached. Then rapidly cut
through the placenta that covered the lower anterior wall of the uterine
cavity, and got the fetus out immediately. A healthy female fetus was
delivered with Apgar scores 9,10 and birth weight 2450g. The placenta
was sequentially checked to confirm diagnosis of vasa previa on the spot
at delivery, and postoperatively by pathology gross
examination(Figure.1\textbf{e} ) before pathological sectioning. The
postoperative course of the patient and the infant was uncomplicated and
they were discharged 3 days later in a healthy condition.

\textbf{Discussion}

Vasa previa can be classified into two types. Type I vasa previa refers
to velamentous insertion of the cord with resultant vasa previa, and
Type II indicates interconnecting vessels between two lobes of placenta
in a bipartite placenta or connecting vessel with a succenturiate lobe
of the placenta\textsuperscript{{[}6{]}}. The parachute placenta with
vasa previa in our case was a little special. The previa vessel
originated for the cord directly like the Type I. But that vessel
doesn't carry the major umbilical blood flow, as it was only a small
branch of the three main umbilical vessels(one umbilical vein and two
umbilical arteries). In this aspect, it was more like Type II vasa
previa. Our case could be considered as a transitional type between Type
I and Type II.

The American College of Obstetricians and Gynecologists recommends the
use of color Doppler in patients who are at a high risk for vasa
previa\textsuperscript{{[}7{]}}. The reasons we considered that the
second time of ultrasonic examination hadn't detected the vasa previa
may include the follows, but not limited to.

First, the most common sections for pelvic ultrasonography are standard
horizontal, sagittal, coronal, and oblique sections originate from the
standard ones\textsuperscript{{[}8{]}}. However, from the MRI we know
the previa vessel was from the patient's right posterior to left
anterior. If the previa vessel long axis was not just in the ultrasound
section, it would not form a curve image but merely a tiny cross
section. In that circumstance, the color Doppler could only see a round
red or blue signal in small diameter. And this patient's placental lower
margin was also close to the cervical internal os, the previa vessel
signal might disguise itself among the placenta blood flows.

Second, even if the transvaginal probe actually rotated and stayed at
the previa vessel long axis direction of left-anterior to
right-posterior, the ultrasonic definition of transvaginal gray scale
might not be high enough to distinguish the
vessel\textsuperscript{{[}9{]}}. In that circumstance, the color Doppler
could help. But color Doppler scanning should be turned on before the
transvaginal probe rotation. Also the lower uterine segment hadn't
formed well because of low lying placenta. Thus, the previa vessel was
not just over the cervical internal os, but posterior to the relatively
thick cervix in transvaginal scanning, bringing more difficulty to
identify it.

Third, as mentioned above, our case was between Type I and Type II, and
the previa vessel only carried a small portion of the umbilical blood
flow. Thus, the blood flow in that previa vessel even might not be
continuous but intermittent. Thereby, if there was just no obvious blood
flow at the time gap during ultrasonic scanning, the vasa previa could
still not be identified\textsuperscript{{[}10{]}}.

MRI can be an alternative in identifying vasa previa, if the ultrasound
scanning results are contradictory\textsuperscript{{[}11{]}}. MRI has
some advantages in this field\textsuperscript{{[}12{]}.} First of all,
it is tomography\textsuperscript{{[}13{]}}. So the image definition for
spatial structures and soft tissues will be able to detect a really thin
vessel. Second, the image can be reconstructed in three
dimensions\textsuperscript{{[}14{]}}. Therefore, any direction of the
previa vessels' courses can be confirmed, not like the ultrasonography
that needs the previa vessel's long axis within the certain scanning
section to see the vessel curve. Meanwhile, the disadvantage of MRI in
this field is unawareness of the blood flow direction, unlike the
ultrasonography with color Doppler\textsuperscript{{[}15{]}}.

In conclusion, vasa previa results in poor pregnancy outcomes if not
diagnosed prenatally. Ultrasonography, especially transvaginal scan with
color Doppler is commonly used as diagnostic method. But if there's
contradictory ultrasonography results, MRI may offer some assistance in
diagnosis.

\textbf{Disclosure of interests}

None. All the authors have no conflict of interest.

\textbf{Contribution to authorship}

Wu Jiahan offered the prenatal care visits for the patient, analyzed the
patient's MRI and ultrasonography results, and wrote the case report.
Hong Ling, assisted in planning the treatment and the cesarean section,
also took the pictures.

\textbf{Details of patient's consent}

The patient has submitted written informed consent for this case report
publication.

\textbf{Funding}

2019 Medical and Health Research Project of Zhejiang Province(2019ZH008)

\textbf{Details of ethics approval}

This report is approved by the Ethics Committee of Ningbo Women and
Children Hospital(approval number 2021No.28, Date 2021.05.25).

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