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Diagnosis of arterio-arterial anastomosis in monochorionic twin by three-dimensional power Doppler ultrasonography

Monochorionic gestations have 3–10 times higher morbidity and mortality rates than dichorionic gestations, in the presence of vascular anastomoses [1]. Twin-to-twin transfusion syndrome (TTTS) complicates 10–15% of monochorionic gestations and, if not treated, has a survival rate of only 20% [2]. Superficial anastomoses, mainly the arterio-arterial anastomosis (AAA), connect twin circulation at the level of the chorionic layer and allow a bidirectional flow. Arterio-venous anastomoses (AVA) are located at the level of cotyledons and allow a unidirectional flow [3]. AAAs seem to protect monochorionic gestations against the onset of TTTS, as bidirectional anastomoses compensate for the hemodynamic imbalance given by unidirectional anastomoses. That is shown by the small frequency of AAAs in monochorionic placentae of TTTS cases [4]. AAA can be identified in prenatal by means of pulsed Doppler observing the characteristic bidirectional interference pattern [5]. There is no description in medical literature on the use of threedimensional ultrasonography (3DUS) with power Doppler (3D power Doppler) in prenatal diagnosis of AAA. We present a case of monochorionic and diamniotic twin gestation with the onset of TTTS on the 29th week. AAA was suspected, by pulsed Doppler, and later confirmed in postnatal by means of a dye-contrast injection. We emphasise the main findings of AAA at 3D power Doppler. A 30-year-old patient, primigravida, has performed a transvaginal ultrasound at the 8th week that showed a monochorionic and diamniotic twin gestation. Later, ultrasonographic examinations showed adequate growth of both fetuses, with normal fluid volume. On the 29th week, obstetric ultrasound showed estimated fetal weight discordance (Fetus 11⁄4weight percentile 95 and Fetus 21⁄4weight percentile 6, according to Hadlock et al.’s table [6]) with normal fluid volume in both amniotic sacs. Using Doppler, it was found that Fetus 2 had centralization hemodynamics [PI MCA (median cerebral artery)/PI UA (umbilical artery) 51,0] in arterial evaluation, and venous evaluation (ductus venous) was normal. On the 32nd week, there was an impairment of Doppler velocimetry parameters, and US Doppler showed reversed-end diastolic flow. Severe growth restriction of Fetus 2 (weight percentile 3) was also found, and the volume of amniotic fluid was still normal, though on the lowest level of normality (percentile 5, according to Moore and Cayle’s table [7]). A real-time sweep was performed at the level of the chorionic layer of the placenta using color Doppler, and a vessel communicating with both umbilical cords was found. Pulsed Doppler mode identified the bidirectional pattern