Ultrasound-Guided Fetal Surgeries: Techniques and Applications

Ultrasound-guided fetal surgeries are among the least invasive options for fetal interventions. The key to successfully completing these procedures lies in achieving a clear ultrasound view of the target, aligned with the chosen uterine entry point. This entry path must steer clear of maternal organs, such as the bowel, bladder, and maternal vasculature. Occasionally, passage through the placenta is intentional, but it's preferably avoided. These interventions take place in an operating room to facilitate anesthesia support, ensure better visualization, and provide access to additional instruments should complications arise.

In this chapter, we discuss shunt placement for lower urinary tract obstruction and fetal primary pleural effusion. We then elaborate on two major techniques for selective fetal reduction. Lastly, the prenatal treatments for cardiac anomalies, placental chorioangioma, and vein of Galen malformation are explored. Intrauterine fetal transfusion, another ultrasound guided fetal procedure is addressed in a separate VISUOG chapter.
 

Lower urinary tract obstruction and vesico-amniotic shunt:
Q64.2 Congenital posterior urethral valves
Q64.3 other atresia and stenosis of urethra and bladder neck
Q64.5 Congenital absence of bladder and urethra
Q64.9 Congenital malformation of urinary system, unspecified
O35 Maternal care for known or suspected fetal abnormality and damage
O35.9 Maternal care for (suspected) fetal abnormality and damage, unspecified
 

Fetal pleural effusion and thoraco-amniotic shunt:
P28 other respiratory conditions originating in the perinatal period
P28.8 Other specified respiratory conditions of newborn
O35 Maternal care for known or suspected fetal abnormality and damage
O35.9 Maternal care for (suspected) fetal abnormality and damage, unspecified
 

Selective fetal reduction
O31 Complications specific to multiple gestation
O31.1 continuing pregnancy after abortion of one fetus or more
O31.8 other complications specific to multiple gestation
O43.0 Placental transfusion syndromes
 

Vein of Galen malformation
Q28.2 Arteriovenous malformation of cerebral vessels
O35.0 Maternal care for (suspected) central nervous system malformation in fetus
 

Placental chorioangioma 
O43.1 Malformation of placenta – placental angioma 
 

Cardiac intervention
Q23.0 Congenital stenosis of aortic valve
Q23.4 Hypoplastic left heart syndrome
Q22.0 Pulmonary valve atresia
Q22.6 Hypoplastic right heart syndrome

Lower urinary tract obstruction (LUTO)

Fetal lower urinary tract obstruction (LUTO) is a collection of congenital anomalies that occurs in about 2.2 per 10,000 live births (1). It is characterized by an obstruction of the fetal urethra, leading to enlargement of the fetal bladder, as well as hydronephrosis and hydroureters (Figures 1 and 2). LUTO can lead to severe consequences, including significant morbidity and mortality due to impaired renal function and underdeveloped lungs (pulmonary hypoplasia).

To manage fetal LUTO, a surgical intervention called the vesico-amniotic shunt (VAS) is employed. This procedure diverts urine from the bladder into the amniotic cavity. VAS offers a potential therapeutic option for selected cases, aiming to alleviate the obstruction and preserve proper pulmonary development (2). VAS is often recommended for patients with severe forms of LUTO, such as posterior urethral valves or urethral atresia, where the obstruction impedes the normal flow of urine from the bladder. To achieve favorable outcomes, careful selection of appropriate patients and ensuring accurate prenatal diagnosis are crucial (3).
 

Fetal pleural effusion
Fetal pleural effusion refers to the buildup of fluid in the pleural space surrounding a developing lungs of fetus. This condition can be detected through prenatal ultrasound examinations. Understanding the root causes of fetal pleural effusions, ensuring timely prenatal diagnosis, and adopting appropriate management strategies are vital for optimizing outcomes for affected fetuses. Various factors can contribute to fetal pleural effusions, including chromosomal abnormalities, genetic disorders, infections, structural cardiac abnormalities, or isolated instances, termed primary or idiopathic pleural effusions. These factors can disrupt the normal balance between pleural fluid production and absorption, leading to fluid accumulation in the pleural cavity. Supplementary diagnostic examinations, such as fetal MRI, genetic testing, and infectious diseases panel, might be necessary to identify the underlying causes.

The severity of this condition can vary. It ranges from mild cases that may resolve spontaneously, moderate cases that can be monitored without intervention, to severe cases that require medical treatment. Severe forms can lead to significant consequences, such as notable morbidity and mortality, because they can compress the heart and large vessels, compromising pulmonary function (4). The treatment choice hinges on the underlying cause and its potential impact on the fetus's health. In some instances, interventions like fetal thoracentesis might be essential. Close monitoring and collaboration with a team of healthcare professionals experienced in fetal medicine are crucial to assess the condition and determine the best approach for the fetus's well-being (5).

General concept of shunt placement
For managing severe and recurrent fetal pleural effusions, a surgical intervention known as the thoraco-amniotic shunt (TAS) is used. This procedure drains fluid from the fetal thoracic cavity into the amniotic cavity. TAS offers a promising therapeutic option for specific cases, aiming to relieve pressure in the thoracic cavity, enhance cardiac function, foster lung development, and improve neonatal outcomes (6).

As a preliminary step, both TAS and VAS procedures can be preceded by a bladder tap and chest tap, respectively. These preliminary measures allow for the examination of fluid re-accumulation in the respective spaces and facilitate analysis of the fluid content (3). The placement of a VAS or TAS entails a minimally invasive percutaneous ultrasound-guided shunt insertion.

For patients with LUTO, the initial step requires amnioinfusion to create a potential space for the shunt's distal end. This stage can pose challenges, as it necessitates precise placement of the needle tip into the amniotic space to prevent infusing fluid outside it (extra-membranous) or into the fetal tissue. Unlike VAS, TAS placement does not require amnioinfusion since pleural effusions typically accompany polyhydramnios rather than oligohydramnios.

Throughout the procedure, the introducer is guided into the desired fetal space (either bladder or pleura). The proximal pigtail end is then deployed. The introducer is subsequently retracted to the amniotic space and positioned slightly offset from the fetal body wall. For VAS, the shunt is optimally positioned in the lower portion of the fetal bladder (Figure 3). Conversely, for TAS, it is directed through the intercostal space, preferably medially or inferiorly to the scapula in the midline, to ensure efficient drainage and minimize the risk of dislodgment (Figure 4, Video 1). The entire procedure of VAS placement is depicted in Video 2. The intramuscular injection of fetal anesthetic agent is also shown in Video 3.

The success of the shunt is primarily evaluated by observing the decompression of fluid from the drained space. For VAS, improvement in amniotic fluid volume can be seen, while for TAS, resolution of fluid accumulation in other body compartments and improved cardiac function may be observed (Figure 5). Prenatal and postnatal monitoring, coupled with fetal MRI, assist in evaluating the shunt's efficacy.

Potential complications during the procedure can encompass misplacement of the shunt with the distal end being dislodged into the maternal uterine wall or abdomen, the possibility of injuring maternal or fetal organs or vessels, and the shunt winding around and constricting fetal limbs (7, 8). Post-operative complications might entail shunt dislodgment (Figure 6) (9), obstruction necessitating further interventions, preterm labor, placental abruption, infection, and premature membrane rupture. Close follow-up and prompt intervention are necessary to address these complications.

This section discusses selective reduction in the context of monochorionic pregnancies. Selective fetal reduction is a medical procedure performed during a multiple pregnancy to decrease the number of fetuses, aiming to enhance the chances of a healthy outcome for both the pregnant person and the remaining fetuses. Indications for selective reduction in monochorionic twins can include, but are not limited to, structural or genetic fetal anomalies, selective fetal growth restriction (sFGR), Twin-twin transfusion syndrome (TTTS), and twin anemia polycythemia (TAPS). Additionally, selective reduction may be considered as a treatment for twin reversed arterial perfusion syndrome (TRAP) to reduce the acardiac twin and improve the outcome of the pump twin.

When multiples share a placenta, reducing a single fetus requires specific methods to avoid harming the remaining fetus. This process involves stopping the blood supply to the reduced fetus, which can be achieved through various energy-transforming procedures: 

Radiofrequency ablation (RFA)
RFA, or radiofrequency ablation, is a minimally invasive procedure used to reduce the number of fetuses in a pregnancy. It deactivates targeted fetal tissue using thermal energy from radiofrequency waves. The procedure is typically carried out under the guidance of ultrasound imaging. An ultrasound-guided needle electrode is inserted into the target fetus, facilitating real-time visualization of the procedure. The electrode then connects to a radiofrequency generator, which emits waves to produce heat. This heat aims to ablate the targeted tissue, often focusing on the fetal umbilical cord or other vital structures. The procedure is depicted in Video 4.

Radiofrequency ablation for selective fetal reduction offers several benefits. These include its minimally invasive nature, the precision with which specific fetal structures can be targeted, and the potential to preserve the amniotic sac and placenta for the remaining fetuses (10). Furthermore, RFA can be performed relatively early in the pregnancy, serving as an option to mitigate risks associated with higher-order multiple pregnancies.
 

Bipolar cord coagulation
This is an alternative method utilized for selective fetal reduction. The procedure entails using bipolar forceps to coagulate and block the blood flow within the umbilical cord of the targeted fetus, resulting in the cessation of blood circulation and eventual fetal demise (11). The procedure is typically conducted under the guidance of ultrasound imaging. Bipolar forceps, equipped with two electrically conductive tips, are introduced into the amniotic cavity and guided to the umbilical cord of the targeted fetus. The forceps are then positioned to grasp and coagulate the blood vessels of the cord, thereby interrupting the blood supply to the fetus. Compared to RFA, bipolar coagulation may be more technically challenging but is preferred in some cases, such as monoamniotic pregnancies, to prevent intertwin cord entanglement. 

It is crucial to emphasize that both RFA and bipolar coagulation for selective fetal reduction or treatment of the TRAP sequence should only be performed by experienced healthcare professionals specialized in fetal interventions. The procedure necessitates careful patient selection, thorough counseling, and consideration of potential risks and benefits. While RFA and bipolar coagulation for fetal selective reduction are generally considered safe and effective, they carry potential complications. These include the risk of infection and bleeding at the insertion site for the pregnant patient, potential injury to adjacent maternal structures, including the uterus, and placental abruption. Fetal complications affecting the remaining fetuses, such as injury or premature labor, should also be considered. There is also a chance of failure to achieve the desired reduction. It is essential for individuals considering these procedures to have open and detailed discussions with their healthcare provider to fully understand these potential complications, their likelihood, and the individualized risks involved to make informed decisions about their care. 

Ethical considerations surrounding selective fetal reduction are also relevant since it involves the selective termination of potentially viable pregnancies. Ethical discussions, informed consent, and appropriate psychological support should be provided to the parents throughout the decision-making process.

Intrauterine treatment for the vein of Galen malformation (VOGM) is a specialized medical approach aimed at managing this rare congenital vascular anomaly affecting the brain. VOGM is characterized by an abnormal connection between the arteries and veins in the brain, leading to a high-flow arteriovenous malformation.

In certain cases, intrauterine treatment may be considered for VOGM to address potential complications and improve the long-term outcome for the affected fetus. However, it's important to note that intrauterine treatment for VOGM is not widely available and is typically performed under a research protocol at specialized medical centers by a multidisciplinary team, which includes fetal medicine specialists, pediatric neurologists, and interventional radiologists (12). 

The intrauterine treatment for VOGM employs embolization. This procedure, conducted under ultrasound guidance, involves accessing the malformation through a needle inserted into the abdomen and uterus of pregnant patient. Using imaging guidance, small embolic agents or coils are introduced into abnormal vessels of the malformation to reduce blood flow and redirect it to healthier areas of the brain (Figure 7, Video 5 and 6).
The goal of intrauterine treatment for VOGM is to prevent or minimize the development of high cardiac output failure, hydrocephalus, and other associated complications. The procedure is typically performed during the second or third trimester of pregnancy, when the fetus is more developed and better able to tolerate the intervention.

Chorioangiomas are benign vascular tumors that develop in the placenta during pregnancy (Figure 8). These tumors can lead to complications such as fetal anemia, hydrops fetalis, and preterm labor. To address chorioangiomas, a coagulation procedure is employed with the aim of disrupting the blood flow within the tumor to reduce its size. The method used for coagulating chorioangiomas depends on their location, size, and characteristics. These methods include:

•    Laser Coagulation: In certain cases, large chorionic feeding vessels can be observed fetoscopically traveling from the umbilical cord's placental insertion site towards the chorioangioma. Laser energy is delivered through a fiber-optic cable inserted into the tumor via the uterus. This laser energy heats and destroys the blood vessels within the chorioangioma, leading to its coagulation. In some instances, laser coagulation can be performed using fetoscopy to directly coagulate the chorioangioma's feeding chorionic vessels (13). 

•    RFA: This method involves using radiofrequency waves to produce thermal energy, which is then directed into the chorioangioma. The thermal energy heats the tumor tissue, resulting in coagulation and subsequent shrinkage of the chorioangioma (14, 15). 

•    Embolization: This procedure entails injecting substances, such as microspheres or particles, into the blood vessels that supply the chorioangioma. These substances block the blood flow, inducing tumor ischemia and eventual coagulation (16, 17). 

Intrauterine cardiac interventions involve medical procedures conducted on a fetus's heart while it remains in the uterus (18). These interventions are typically recommended when significant cardiac abnormalities or structural defects are detected during prenatal screening or diagnosis. The primary objective of these interventions is to enhance fetal cardiovascular function, improve postnatal outcomes, and potentially reduce the need for more invasive procedures after birth. Various types of intrauterine cardiac interventions can be performed, depending on the specific cardiac abnormality and the expertise of the medical team. The types of cardiac lesions for which prenatal intervention is currently available include:

•    Aortic stenosis with evolving hypoplastic left heart syndrome. The procedure of aortic valvuloplasty by transvalvular balloon inflation is shown in Video 7. 
•    Pulmonary atresia with intact ventricular septum and evolving right ventricular hypoplasia 
•    Hypoplastic left heart syndrome with intact atrial septum (HLHS with IAS) (19)

Aortic and pulmonary valvuloplasties are considered in cases of aortic and pulmonary stenosis, respectively. The goal of fetal intervention in these circumstances is to avoid a univentricular circulation after birth given the morbidity and mortality associated with single ventricle palliation. In contrast, the goal of cardiac intervention for HLHS with IAS is to relieve atrial restriction in order to improve immediate perinatal survival. This may be accomplished by inflating a balloon across the atrial septum and, if desire, by placing a stent in the atrial septum to maintain patency.

All fetal cardiac interventions are performed by a multidisciplinary team, comprising fetal medicine specialists, pediatric cardiologists, and interventional radiologists. They are needle-based interventions guided by advanced imaging techniques, such as ultrasound and fetal echocardiography.

Intrauterine cardiac interventions come with certain risks and considerations that need thorough evaluation. These might include complications related to the procedure itself, the possibility of preterm labor, premature rupture of membranes, and potential harm to the fetus. Hence, before proceeding with these interventions, it is crucial to engage in careful patient selection, offer comprehensive counseling, and conduct a thorough assessment of potential risks and benefits. While intrauterine cardiac interventions are promising in specific cases, they are still relatively new and specialized. Ongoing research and technological advancements are continually refining the techniques and expanding the scope of these interventions. Proper evaluation of long-term outcomes and meticulous follow-up care are essential to assess the effectiveness and impact of intrauterine cardiac interventions on both fetal and postnatal well-being.

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