MRI findings in multifetal pregnancies complicated by twin reversed arterial perfusion sequence (TRAP)

Rare Case of Twin Reversed Arterial Perfusion Acardius Acephalus Subtype Seen in a Community-Based Hospital

Background  TRAP sequence occurs in monochorionic pregnancies consisting of one normal fetus and a non-viable fetus. The pump twin has an increased risk of developing high-output cardiac failure. Case  32-year-old G4P2012 with TRAP syndrome in current pregnancy presented to triage at 26 weeks with contractions and spotting. She had undergone RFA for selective reduction at another facility. Placental abruption was suspected and patient underwent a cesarean section. Twin A was delivered alive although she subsequently succumbed due to complications of prematurity. Conclusion  This case highlights the importance of early detection and consistent prenatal care in the management of TRAP sequence. Further research of interventions associated with improved outcomes should be encouraged.

Fetal magnetic resonance imaging, ultrasound, and echocardiography findings in twin reversed arterial perfusion sequence

BACKGROUND

Twin reversed arterial perfusion (TRAP) sequence is a rare complication of monochorionic multiple gestation pregnancies, in which the pump twin provides hemodynamic support to a nonviable co-twin (acardius). Fetal magnetic resonance imaging (MRI) is used to detect pump twin abnormalities, particularly brain ischemia, prior to fetal intervention to interrupt umbilical blood flow to the acardius.

OBJECTIVE

To summarize the imaging findings of TRAP sequence pregnancies in a large series.

MATERIALS AND METHODS

A single-center retrospective review was performed of all TRAP sequence pregnancies referred for fetal MRI (2004-2021). Fetal MRI, ultrasound, and echocardiography data were collected.

RESULTS

Eighty-eight TRAP sequence pregnancies with MRI were included (mean gestational age, 19.8±2.8 weeks). Demise of the pump twin was noted in two pregnancies at the time of MRI. By MRI, 12% (10/86) of live pump twins had abnormalities, including 3% (3/86) with brain abnormalities and 9% (8/86) with extra-cranial abnormalities. By echocardiography, 7% (6/86) of pump twins had structural cardiac abnormalities. Three acardius morphological subtypes were identified by MRI: acephalus (55%, 48/88), anceps (39%, 34/88), and amorphous (7%, 6/88). The mean ultrasound acardius to pump twin ratio A/P ratio, calculated for each twin pair as the ratio of the acardius trunk (and head, if present) plus limb volume to the pump twin estimated fetal weight) differed among the three acardius subtypes (P=.03). The mean A/P ratio moderately correlated with pump twin cardiothoracic ratio and combined cardiac output (Pearson's r=0.45 and 0.48, respectively, both P<.001).

CONCLUSION

Fetal MRI of TRAP sequence pregnancies found anomalies in a substantial number of pump twins. The three acardius subtypes differed in A/P ratio, which moderately correlated with the pump twin cardiothoracic ratio and combined cardiac output.

"The Strange Case of Dr Pump and Mr Acardiac": The Twin Reversed Arterial Perfusion (TRAP) Sequence in Two Monochorionic Monoamniotic (MCMA) Twin Pregnancies-Diagnosis, Prognosis and Management: Review of Literature

The Twin Reversed Arterial Perfusion (TRAP) Sequence is an extremely rare complication of monochorionic twin pregnancies, with one severely malformed twin (the "acardiac") lacking autonomous placental blood supply and being perfused by the co-twin (the "pump"), through arterio-arterial (and sometimes also veno-venous) vascular anastomoses located on the placental surface. The prognosis is poor: mortality is 100% in the acardiac twin because of its severe malformations and about 50-55% in the pump twin, mainly due to heart failure and prematurity. So, the goal of perinatal management of the TRAP twin pregnancy is to deliver a healthy and near-term pump twin without heart failure or fetal hydrops. Intuitively, the earlier the diagnosis, the better the outcome. Herein, we report two cases of monochorionic monoamniotic (MCMA) twin pregnancies complicated by the TRAP Sequence, which are of interest since the objective of early diagnosis was achieved by means of transvaginal and 3D ultrasound, two techniques which revealed themselves as being useful to this purpose but are underused in the literature. The second aim of this study is to provide an overview of literature data about the diagnosis, prognosis establishment, and management of this rare condition, which are still debated and unclear due to negligible poor-quality evidence.

Twin reverse arterial perfusion: Timing of intervention

Twin reverse arterial perfusion (TRAP) sequence is a severe anomaly in monochorionic twins where one twin has profound corporeal underdevelopment and acardia. The normal "pump" co-twin provides blood flow to the acardiac twin through placental anastomoses which may lead to cardiac failure and pump twin demise as well as preterm delivery from severe polyhydramnios. Treatments include radiofrequency ablation, bipolar cord coagulation, and intrafetal laser with each aimed at occluding blood flow to the acardiac twin. However, none of these modalities has proven superior in terms of either pump twin survival or minimization of complications, including preterm premature rupture of membranes, preterm birth, or unexpected co-twin demise. The optimal timing of treatment is also unknown, without clear indications for intervention versus expectant management. Very early treatment of TRAP (i.e., <16 weeks) has been proposed to reduce first-trimester demise; however, this approach remains experimental. Further investigation is required to determine the best treatment and timing of intervention for TRAP.

Hypothesized pathogenesis of acardius acephalus, acormus, amorphus, anceps, acardiac edema, single umbilical artery, and pump twin risk prediction

Background

Acardiac twinning complicates monochorionic twin pregnancies in ≈2.6%, in which arterioarterial (AA) and venovenous placental anastomoses cause a reverse circulation between prepump and preacardiac embryos and cessation of cardiac function in the preacardiac. Literature suggested four acardiac body morphologies in which select (groups of) organs fail to develop, deteriorate, or become abnormal: acephalus (≈64%, [almost] no head, part of body, legs), amorphus (≈22%, amorphous tissue lump), anceps (≈10%, cranial bones, well‐developed), and acormus (≈4%, head only). We sought to develop hypotheses that could explain acardiac pathogenesis, its progression, and develop methods for clinical testing.

Methods

We used qualitatively described pathophysiology during development, including twin‐specific AA and Hyrtl's anastomoses, the short umbilical cord syndrome, high capillary permeability, properties of spontaneous aborted embryos, and Pump/Acardiac umbilical venous diameter (UVD) ratios.

Results

We propose that each body morphology has a specific pathophysiologic pathway. An acephalus acardius may be larger than an anceps, verifiable from UVD ratio measurements. A single umbilical artery develops when one artery, unconnected to the AA, vanishes due to flow reduction by Hyrtl's anastomotic resistance. Acardiac edema may result from acardiac body hypoxemia combined with physiological high fetal capillary permeability, high interstitial compliance and low albumin synthesis. Morphological changes may occur after acardiac onset. Pump twin risk follows from UVD ratios.

Conclusion

Our suggested outcomes agree reasonably well with reported onset, incidence, and progression of acardiac morphologies. Guidance for clinical prediction and testing requires ultrasound anatomy/circulation study, from the first trimester onward.

A Taiwan's experience: A case report and review of literature of successful early intrauterine treatment with radiofrequency ablation in twin reversed arterial perfusion (TRAP) sequence

Acardiac twin or twin reversed arterial perfusion (TRAP) sequence is a rare medical complication of Monozygotic twins. Taiwanese Obstetricians usually treat TRAP sequence conservatively. Occasionally, repeated amnio-reduction is performed to decompress the polyhydramnios caused by the TRAP sequence, even though there was no correction of the pathophysiologic mechanism. Radiofrequency ablation is a minimally invasive, percutaneous technique that can effectively obliterate blood supply to an acardiac twin to preserve and protect the pump twin. This recent technique has never been used before for the treatment of the TRAP sequence in Taiwan. This article reported the first-hand experience of acardiac twin management with RFA in Taipei Chang Gung Memorial Hospital.

Morphology, intrafetal vascular pattern, and umbilical artery Doppler indices of acardiac twins

BACKGROUND

Twin reversed arterial perfusion (TRAP) sequence consists of acardiac twin (A) paradoxically perfused by pump twin (P) through an umbilical artery (UA). We proposed characterization of acardiac twins with intrafetal vascular pattern (IVP), and assessed its correlation with morphology and UA Doppler indices.

METHODS

We prospectively evaluated 21 cases of TRAP sequence. Morphology (acardia vs hemicardia) and IVP (simple vs complex) of acardiac twins were characterized with ultrasound and color Doppler. Twins weight ratio (A/P Wt) and UA Doppler indices of acardiac and pump twins including (1) difference of systolic/diastolic ratio (UA ∆S/D), (2) difference of resistance index (UA ∆RI), and (3) ratio of pulsatility index (UA PI A/P) were calculated.

RESULTS

The median (min, max) gestational age at diagnosis was 18 (11, 27) weeks. Acardia (n = 14) were associated with simple IVP (n = 16) (P < .05). After exclusion of acardia with complex IVP (n = 1), the A/P Wt, UA ∆S/D, UA ∆RI, and UA PI A/P of acardia with simple IVP (n = 13), hemicardia with simple IVP (n = 3), and hemicardia with complex IVP (n = 4) were not significantly different (P > .05).

CONCLUSIONS

Most of acardiac twins were acardia with simple IVP. Morphology and IVP of acardiac twins were not associated with UA Doppler indices.

Fetal MRI: A pictorial essay

Ultrasonography (USG) is the primary method for antenatal fetal evaluation. However, fetal magnetic resonance imaging (MRI) has now become a valuable adjunct to USG in confirming/excluding suspected abnormalities and in the detection of additional abnormalities, thus changing the outcome of pregnancy and optimizing perinatal management. With the development of ultrafast sequences, fetal MRI has made remarkable progress in recent times. In this pictorial essay, we illustrate a spectrum of structural abnormalities affecting the central nervous system, thorax, genitourinary and gastrointestinal tract, as well as miscellaneous anomalies. Anomalies in twin gestations and placental abnormalities have also been included.

Guidelines for scanning twins and triplets with US and MRI

Multiple-fetus gestations have an increased risk of discordant anomalies, aneuploidy and growth restriction compared to singleton pregnancies. In addition, twins sharing the same placenta are at risk for developing specific conditions that are potentially amenable to surgical management. In those scenarios, patients might need to be evaluated not only with US but with fetal MRI as well. This paper outlines basic guidelines to consider when imaging complicated multiple-fetus gestations during the 2nd and 3rd trimesters.

Twin Reversed Arterial Perfusion Sequence: A Rare Entity

Twin reversed arterial perfusion (TRAP) sequence is an extremely rare complication of monochorionic multi-fetal pregnancy, occurring once in 35,000 births. This condition is characterized by a malformed fetus without a cardiac pump being perfused by a structurally normal (pump) twin via an artery-to-artery anastomosis in a reverse direction. We report a case of a primigravida, who came for routine antenatal checkup to our hospital at 31 weeks gestational age. Ultrasound imaging and magnetic resonance imaging revealed twin monochorionic intrauterine pregnancy with a viable, normal-appearing first twin and amorphous structured second twin connected by umbilical vessels. The patient was monitored with weekly ultrasonography, echocardiography, and Doppler ultrasound examination to ascertain the well-being of the pump twin. She delivered successfully at term a normal live baby and an acardius acephalus fetus. Plain X-ray of the acardius acephalus fetus confirmed the absence of cephalic structures. The perinatal mortality of the pump twin ranges from 35 to 55%; hence, it is essential to diagnose the presence of a pump twin at an early gestational age through improved imaging techniques, so that intervention can be planned early in the pregnancy for a better outcome of the pump twin.

The developing role of fetal magnetic resonance imaging in the diagnosis of congenital cardiac anomalies: A systematic review

Advances in the fetal magnetic resonance imaging (MRI) over the last few years have resulted in the exploring the use of fetal MRI to detect congenital cardiac anomalies. Early detection of congenital cardiac anomalies can help more appropriately manage the infant's delivery and neonatal management. MRI offers anatomical and functional studies and is a safe adjunct that can help more fully understand a fetus' cardiac anatomy. It is important for the obstetricians and pediatric cardiologists to be aware of the recent advancements in fetal MRI and it`s potential utility in diagnosing congenital cardiac anomalies.