Keywords
twin–twin transfusion syndrome - polyhydramnios - microseptostomy - monochorionic
- multifetal gestation
A 30-year-old, gravid 4, parity 2012 presented for care in the first trimester with
a confirmed monochorionic, diamniotic twin gestation. Biweekly ultrasounds were initiated
for twin–twin transfusion syndrome (TTTS) surveillance. Between 16 and 20 weeks, both
fetuses demonstrated normal growth and amniotic fluid volumes. Fetal anatomic evaluation
did not identify any congenital malformations. At an estimated gestational age of
20 weeks 3 days, polyhydramnios was noted for both fetuses, with the maximum vertical
pocket (MVP) being 10.1 cm for fetus A and 10.3 cm for fetus B. Additionally, the
bladder in fetus A could not be visualized, and the bladder of fetus B was subjectively
enlarged. Persistent absent end diastolic flow (AEDF) in the umbilical artery was
noted on Doppler sonography for fetus B. Both fetuses demonstrated appropriate growth
and were concordant for gestational age.
At 215/7 weeks, the bladder of twin A was still not visualized, polyhydramnios had significantly
worsened for both fetuses (MVP 15.0 and 15.4 cm for fetus A and B, respectively),
and persistent reversed end diastolic flow (REDF) in the umbilical artery was noted
for fetus B. The patient was referred to a fetal treatment center secondary to the
concern for a nonclassic presentation of TTTS. Ultrasound findings were confirmed,
and the possibility of TTTS was discussed.
At 223/7 weeks, the patient underwent amniocentesis and subsequent 1-L amnioreduction with
injection of indigo carmine into the amniotic sac of fetus A. Amniocentesis and amnioreduction
were then performed for fetus B. Spontaneous communication between the two amniotic
sacs was confirmed when dye was noted to be present in the amniotic fluid removed
from fetus B ([Fig. 1]). Of note, the membranes had previously appeared intact on multiple prior sonographic
evaluations, and so the etiology was felt to be a spontaneous, idiopathic microseptostomy.
Fig. 1 (A) The amniotic fluid of twin A was initially noted to be clear, though indigo carmine
was injected into the sac at the conclusion of the procedure. However, (B) indigo
carmine was present in the amniotic fluid of twin B during the amniocentesis for that
twin, as evidenced by the color, demonstrating the presence of a microseptostomy despite
no gross communication being present either on ultrasound or even pathologic evaluation
of the membranes postdelivery.
Follow-up ultrasound evaluation at 225/7 weeks demonstrated no change in postprocedural fluid volumes and persistent REDF
for fetus B; however, a small cycling bladder was now seen for fetus A. Repeat evaluation
at 231/7 weeks revealed AEDF in the ductus venosus of fetus B. The patient was presented with
the option of either serial amnioreduction for maternal comfort or selective reduction
of fetus B and opted for intermittent amnioreduction and returned to her local provider.
Repeat examination at 235/7 weeks demonstrated worsening of the TTTS with a recurrence of polyhydramnios (MVP
15.9 and 15.5 cm for fetus A and B, respectively) and nonvisualization of the bladder
of fetus A. Fetus B had persistent REDF and an enlarged heart with decreased contractility.
The patient was informed of the guarded prognosis and opted to return to the referral
center the next day, where she was subsequently diagnosed with a dual demise and underwent
labor induction. The subsequent placental pathology demonstrated a total of four arterial-venous
anastomoses, two present in each direction. The fetal membranes appeared visually
intact on gross examination. The final karyotype was normal and the fetal autopsy
was also consistent with a diagnosis of TTTS with evidence of chronic vascular overload
in twin B (plethoric appearance, cardiomegaly, and dilated bladder) and anemia in
twin A (pallor, reduced bladder and heart size).
Discussion
The presence of polyhydramnios and oligohydramnios in a set of monochorionic twins
is both pathognomonic for and lies at the heart of the sonographic definition of TTTS.[1] However, TTTS can both present in monoamniotic gestations or persist after intentional
septostomy.[2] Thus in the setting of a communication between the amniotic cavities of the two
fetuses, the underlying pathophysiology of TTTS can exist and worsen in the absence
of a classic polyhydramnios and oligohydramnios appearance.
With a known monoamniotic gestation or after an intentional septostomy, the provider
is aware of the communication between the amniotic cavities and thus the potential
that the donor may not manifest oligohydramnios. In the presented case, however, the
patient had not previously undergone an invasive procedure and a communication could
not be identified sonographically. Though uncommon, spontaneous septostomies have
been reported in diamniotic twin gestations,[3] even resulting in cord entanglement at the time of delivery.[4] Yoshimura et al and Chmait et al previously reported cases of TTTS in which the
donor twin manifested either polyhydramnios or normal amniotic fluid volumes secondary
to the occurrence of a spontaneous septostomy.[5]
[6] In these cases, the septostomy had been apparent either prior to delivery or at
the time of fetoscopy. In the presented case, the providers were aware of the potential
for the unusual TTTS presentation to have been the result of a spontaneous septostomy,
and thus several careful attempts were made by different providers to identify one.
No septostomy, however, was ever directly visualized prior to delivery or even on
gross examination of the placenta itself. The fact that indigo carmine was able to
transfer from the sac of one twin to the other demonstrated the presence of spontaneous
microseptostomies that were too small to visualize. The sonographic appearance, unfortunate
clinical course, and placental pathologic findings all otherwise supported the diagnosis
of TTTS.
In conclusion, practitioners managing patients with monochorionic-diamniotic twin
gestations should be aware of the potential for nonclassic sonographic manifestations
of TTTS secondary to the occurrence of spontaneous microseptostomies. This is true
even if one is unable to directly visualize such septostomies sonographically, because
small amniotic defects may elude detection, as in the current case. If the appearance
of the fetuses is otherwise consistent with TTTS, the presence of an undiagnosed septostomy
has the potential to generate diagnostic confusion and potentially delay the onset
of appropriate therapy. The presence or absence of microseptostomies can be determined
through the use of indigo carmine.
