Anastomoses

Anastomoses within the sac of the donor twin

Vascular communications may be found within the sac of the donor twin in approximately one-thrid of patients with TTTS. 

In these patients, the anastomoses may take one of several forms: 

• Terminal end visible. In these patients, the terminal end of the vessels and, thus, the actual site of the anastomosis, can be seen. Branching prior to the anastomosis may or may not exist, but does not interfere with access to the terminal end. 

• Terminal end not visible. In these patients, the terminal end of the vessel is not visible, whether because of extensive branching of the recipient vasculature within the sac of the donor, or because of donor interference. 

Depending on the presenting form, anastomoses within the sac of the donor may be photocoagulated in one of three ways: 

1. Lasering within the sac of the recipient twin. This is done, provided that photocoagulation within the sac of the recipient twin does not compromise any individually perfused areas of the recipient twin. This is usually reserved for patients in situations where the terminal end is visible and there are no branches within the sac of the donor before the anastomosis (Figure 9.13a). 

2. Lasering within the sac of the donor twin. This is done if lasering within the sac of the recipient twin would result in photocoagulation of recipient-perfused areas within the sac of the donor twin. This would typically occur in cases of numerous anastomoses within the sac of the donor or with extensive branching and inaccessibility to the actual terminal end. For this, an amnioinfusion of the sac of the donor twin is first done, followed by trocar insertion into the sac of the donor twin. We prefer to use a similar-size trocar and endoscope, to allow full disclosure of the anastomoses. Since the anastomoses have been identified and mapped from within the sac of the donor, a dual camera approach can be used with an assistant to monitor the process (Figure 9.13b,c). 

3. Selective photothermolysis. In this technique, with the endoscope in the sac of the recipient twin, the laser beam is aimed at the visible terminal end of the vessel in the sac of the donor twin and the YAG laser is fired through the membrane against the vessel (Figure 9.13d). Photocoagulation of the vessel takes place without injury to the membrane. The physical principle of this technique is the absorbance of YAG laser energy by color. Since the membranes are transparent, the laser beam goes through the membrane without being absorbed. It is important to note here that injury to the membrane may occur if bleeding within the sac of the donor has occurred previously, as even hemosiderin deposits would be enough to produce absorption of the laser energy.