Selective laser photocoagulation

Selective laser photocoagulation of communicating vessels in patients with an anterior placenta

An anterior placenta presents additional technical challenges in patients undergoing percutaneous SLPCV for severe TTTS. The challenges consist of finding a placenta-free area in the anterior uterine wall through which the trocar can be inserted and being able to assess all vascular communications from that entry site. Finding a placenta-free area in the anterior wall may be difficult, particularly if the placenta is widely extended. 

In addition, anterior placentas may also ‘wrap around’ the lateral walls, precluding free access to the amniotic cavity. Approaches to the treatment of patients with anterior placentas that cannot be addressed with a straight operating endoscope have included performing a wide laparotomy with forward flipping of the uterus and entry into the amniotic cavity from the posterior wall (De Lia, pers comm); performing a mini-laparotomy and inserting a bent cannula;23 use of flexible-steerable operating endoscopes. In 2001 we published on two techniques to address patients with anterior placentas. 

Technique 1: flexible, steerable endoscope 

Technique 1 uses a flexible endoscope through a single port. Under ultrasound guidance, a placentafree area is identified in the anterior uterine wall. A 3 mm trocar is inserted percutaneously in the amniotic cavity of the recipient twin through a minimal skin incision. The placenta is surveyed with diagnostic endoscopes 2.7 mm in diameter, of varying angles of vision: 25° or 70° (angledview endoscopes; Richard Wolf, Inc., Vernon Hills, IL) pointing the deflected angle of vision towards the placenta. All communicating vessels are identified as described above. 

The diagnostic endoscope is then exchanged for a 45 cm flexible- steerable 0° operating endoscope (Richard Wolf) with a 1 mm operating channel. The angle of flexion of the endoscope is 90° in two directions without the laser fiber and approximately 70° when a 400 ?m laser fiber is within the operating channel. The previously identified vessels are photocoagulated by flexing the tip of the endoscope towards the placenta (see Figure 9.5). The placenta is assessed again with the rigid 25° or 70° endoscope to evaluate adequacy of the photocoagulation procedure. 

Technique 2: two-port, side-firing laser fiber 

After the placenta has been surveyed with the angled-viewed endoscopes, a separate 2 mm port is inserted into the amniotic cavity of the recipient twin through an additional placenta-free area of the anterior uterine wall. Entry of this second port is monitored externally with ultrasound, and endoscopically from within the amniotic cavity. A 600 ?m side-firing laser fiber (Surgical Laser Technologies, Montgomery, PA) which fires at a 70° angle is inserted through this port. The fiber is placed beneath the target vessels under endoscopic guidance with the angled-view endoscopes, and the vessels are photocoagulated (see Figure 9.8). 

Assessment of the photocoagulated areas is done with the angled-view endoscopes. Seventytwo patients were treated at our center from July 1997 to December 1999. Thirty-five patients (48.6%) had an anterior placenta. At least one fetus survived in 80% of patients with an anterior placenta (28 of 35) and 75.6% of those with a posterior placenta (28 of 37). This difference was not statistically significant (p > 0.5, df = 1, ?-square test, SPSS 9.0 for Windows, Chicago, IL), although the power of the study was low (power = 4%, nQuery Advisor 3.0, Statistical Solutions Inc., Dublin, Ireland). A total of 1450 patients would be necessary to rule out the null hypothesis with a power of 80% at the 0.05 level. Sixty percent (21 of 35) of patients were treated with technique 1 and 40% (14 of 35) with technique 2. 

At least one fetus survived in 76% (16 of 21) of patients treated with technique 1, and in 86% (12 of 14) of those treated with technique 2. This difference was also not statistically significant (p = 0.67, two-tailed Fisher exact test) (power 6%, with 285 patients required to rule out the null hypothesis with a power of 80% at the 0.05 level). The mean operating time for patients with a posterior placenta in that study was 64.4 minutes (range 22–188, SD 35.51), compared with 81.14 minutes (range 20–172, SD 37.12). 

Patients with an anterior placenta had a significantly longer operating time than patients with a posterior placenta (p = 0.02, Student’s t test). Surgical pathology analysis of the placentas showed only 6 of 72 patients (8.3%) had patent vascular anastomoses, but 5 of those 6 patients belonged to the anterior placenta group. One of these 6 patients had persistent TTTS that required serial amniocenteses and delivery at 26 weeks with 1 fetus surviving, 2 had double intrauterine fetal demise, 1 miscarried, and 1 interrupted the pregnancy due to the development of ventriculomegaly in the donor twin. 

The remaining patient had resolution of the syndrome and delivered two healthy babies at 35 4/7 weeks’ gestation; placental analysis in this patient showed a very small (filiform) patent anastomosis. [Currently, we rarely resort to techniques 1 or 2. Instead, we use the trocar-assisted technique as described above, for patients with anterior placentas that are not amenable to treatment simply with the straight operating endoscope (Figure 9.15a).] Two additional particular issues may arise in patients with anterior placentas. 

First, the donor twin may be stuck against the anterior uterine wall between the chosen placenta-free area and the vascular equator (Figure 9.15b). In this case, circumventing the donor twin to reach the equator may prove difficult or impossible, and another placenta-free area must be sought. A second potential issue may arise from vascular communications located between the site of trocar entry and the tip of the trocar, because the trocar sheath must advance a certain distance into the amniotic cavity in order to maintain access. 

Intraoperatively, it is possible to determine if an incomplete assessment of an anterior placenta has been done, because of the inability to follow all vessels to their terminal end. If the syndrome does not resolve in such cases, repeat laser, serial amniocenteses, or, in extreme cases, umbilical cord ligation may be offered to complete the therapy.