Ultrasound assessment

TTTS. Ultrasound assessment of deep communications and/or superficial anastomoses

There are a few reports on the use of ultrasound to assess deep communications or superficial anastomoses.24 Most studies have been performed on patients without TTTS and anterior placentas, as color Doppler insonation of the placental parenchyma is easier in these patients. 

Deep vascular communications 

The presumed diagnosis of deep placental vascular communications involves color Doppler identification of an arterial vessel coming in one direction, and a venous drainage of the same cotyledon going in an opposite direction (Figure 7.17). While such approach may indeed identify deep vascular communications, it is by no means reliable. 

In-vivo endoscopic assessment of placental vascular anastomoses shows that the course of the vessels on the placental surface is unpredictable. As a result, the participating artery and vein, while seemingly in opposite directions, may actually belong to the same fetus. This notion is precisely why prior statements regarding the endoscopic ability to identify placental vascular anastomoses based on the angle of incidence between the artery and vein were disqualified. 

In extreme cases, non-shared cotyledons may show one of the vessels curving on the surface of the placenta making a complete ‘U-turn’ (Figure 7.18). Sonographically, this would appear as an artery and a vein traveling in opposite directions, suggesting the presence of an AV anastomosis, when, in reality, this is a normally and individually perfused cotyledon. Because of the poor sensitivity of ultrasound in delineating the path of placental vessels, the diagnosis of deep vascular communications is, in our opinion, suspect. 

Superficial vascular anastomoses 

The identification of superficial anastomoses, in particular, of AA anastomoses, has been previously reported.25 As with AV communications, this is best attempted in patients with an anterior placenta. AA anastomoses can be suspected with color Doppler by noting the direction of blood flow towards the transducer from both ends of the vessel. Pulsed Doppler interrogation of the vessel may reveal a characteristic additive waveform resulting from the summation of the two heart beats within the same vessel. 

The identification of VV anastomoses has not been described. The sensitivity for the identification of AA anastomoses has been reported to be as high as 85%.25 However, this figure represents the cumulative sensitivity over several ultrasound examinations in the same patient up to the third trimester. 

In our experience, identification of AA anastomoses is both insensitive and extremely time-consuming, even in patients in which a 50% incidence of AA anastomoses can be predicted (e.g. atypical stage III donor). We have not found any difference in the prognosis of patients treated with laser relative to the presence or absence of AA anastomoses. Thus, the quest for the sonographic identification of AA anastomoses may be of limited diagnostic interest. 

CONCLUSION 

Systematic ultrasound assessment of patients with TTTS allows establishing an adequate diagnosis and prognostic factors. Careful attention to sonographic details is necessary to avoid Figure 7.17 Color Doppler identification of an arterial vessel coming in one direction, and a venous drainage of the same cotyledon going in the opposite direction. (See also color plate section, page xxiv.) common pitfalls. Preoperative mapping is important in the planning of any invasive procedure, particularly in the case of laser therapy.