Twin Reverse Arterial Perfusion Syndrome (TRAPS) is a rare complication of monochorionic twin pregnancies, characterised by the presence of an acardiac twin, with the characteristic imaging finding being a grossly malformed twin with absence of a normal cardiac structure on ultrasound.
Description
Twin Reverse Arterial Perfusion Syndrome (TRAPS), also known as Acardiac Twinning, is a rare complication of monochorionic twin pregnancies (i.e. only seen in monozygotic twin pregnancy). It is characterised by one twin (the ‘pump’ twin) having a normally developing heart and the other twin (the ‘acardiac’ twin) having an underdeveloped or absent heart. Blood flow to the acardiac twin is provided in a reversed manner by the pump twin, leading to gross malformations in the acardiac twin.
Pathogenesis
TRAPS occurs due to abnormal placental vascular connections, leading to reverse blood flow from the pump twin to the acardiac twin. The arterial blood from the pump twin enters the acardiac twin, leading to abnormal development of the latter, particularly the absence of functional cardiac tissue. This reversed arterial perfusion results in the pump twin providing circulation for both twins, which can lead to heart failure.
Subtypes
The acardiac twin in TRAPS can manifest in various forms, including:
- Acardius Acephalus: Most common type, where the head and upper body are absent.
- Acardius Anephus: A trunk is present, but limbs are absent.
- Acardius Amorphous: No recognisable body parts are present.
- Acardius Myelacephalus: Partial upper body and neural tissue present.
Epidemiology, Risk Factors & Associations
- Occurs in approximately 1 in 35,000 pregnancies.
- Monochorionic twin pregnancies are the primary risk factor.
Clinical Features
- Pump twin: Risk of cardiac overload and heart failure, hydrops foetalis.
- Acardiac twin: Absence of cardiac activity and gross malformations.
Complications
- For the pump twin: Risk of cardiac failure, hydrops foetalis, and intrauterine death due to the increased circulatory load.
- For the acardiac twin: Incompatible with life due to severe malformations.
Pathological Features
Histopathology
- Macroscopic: The acardiac twin shows gross malformations, including limb anomalies, body wall defects, craniofacial abnormalities and absent or rudimentary heart.
- Microscopic: No specific findings.
Serology
- No specific serological markers.
Biochemistry
- No specific biochemical markers.
Radiological Features
General Features
- The typical imaging finding is the presence of a grossly malformed twin with the absence of normal cardiac structure on ultrasound.
Ultrasound
- B-mode: The acardiac twin shows severe malformations, often with absent or rudimentary cardiac structures. The pump twin is usually normal but may show signs of cardiac overload.
- Colour Doppler: Shows reverse flow from the umbilical artery of the pump twin to the acardiac twin.
Diagnosis
The diagnosis of TRAPS is made primarily based on ultrasound findings showing a monochorionic twin pregnancy with one normally developing twin and one grossly malformed twin without a functional heart.
Differential Diagnosis
- Twin-to-Twin Transfusion Syndrome (TTTS): Can be differentiated by the presence of two viable foetuses in TTTS, whereas in TRAPS, one foetus is grossly malformed and nonviable.
Management
Management of TRAPS can be challenging and often involves procedures to stop the blood flow to the acardiac twin, such as radiofrequency ablation or ligation of the umbilical cord. Close monitoring of the pump twin is essential to manage potential cardiac overload and heart failure. Management should be performed under the guidance of a specialist in maternal-fetal medicine.