Placenta Accreta Spectrum: The Role of Interventional Radiology in Multidisciplinary Management

Abstract

Placenta accreta spectrum is increasing in prevalence and poses significant risks to obstetric patients. This article defines characteristics, diagnosis, management, and outcomes of placenta accreta spectrum, highlighting interventional radiology's role in its management as part of a multidisciplinary approach.

Placenta accreta spectrum (PAS) describes a dangerous obstetric condition wherein there is abnormal attachment of the placenta to the gravid uterus. The placenta normally adheres to the uterine wall and separates after birth. In PAS, the placenta deeply penetrates the myometrium, preventing normal detachment, and may invade adjacent organs, such as the bladder, in severe cases. ¹ The favored hypothesis why this abnormal attachment occurs is that a defect in the endometrial–myometrial interface leads to a failure of normal decidualization in the region of a uterine scar, resulting in deep anchoring villi and trophoblast invasion. ¹ PAS consists of three subtypes defined by the depth of the abnormal placental penetration. About 60% of cases of PAS are diagnosed as placenta accreta, with chorionic villi adhering to the myometrium; 26% of cases are classified as placenta increta, with the chorionic villi invading the myometrium; placenta percreta is the rarest and most severe, comprising 13% of PAS diagnoses, with chorionic villi completely penetrating the myometrium, and often invading adjacent organs ( Fig. 1 ). ¹

Fig. 1.

The spectrum of placental uterine invasion in placenta accreta spectrum. (Created with BioRender.com.)

Risk Factors

Since the 1960s, rates of PAS have increased 60-fold from 1 in 30,000 pregnancies to 1 in 533 pregnancies, presumably due to increased uterine instrumentation. ² Clinical risk factors for the development of PAS include previous uterine surgeries (such as cesarean delivery, myomectomy, and curettage), placenta previa, history of retained placenta, and multiparity. The potential contribution of these risk factors may be related to a component of hypoxia induced by scar tissue, which thus stimulates trophoblastic invasion. ³

Diagnosis

Ultrasound (US) is commonly utilized in the diagnosis of PAS. Common features of PAS identified by US include a low-lying placenta (including total previa), and imaging can show an absence of normal anechoic or hypoechoic myometrium seen in what is known as the junctional zone. ⁴ With PAS, the placenta will show a heterogeneous echotexture with possible subplacental vascular spaces indicating abnormal placental invasion. Enlarged parauterine veins can also be seen using Doppler imaging. ⁵

Magnetic resonance imaging (MRI) is vital to diagnosis and planning interventions. On MRI, patients with PAS may have an abnormal uterine contour. T2-weighted images may depict thinning of the myometrium and placental invasion or disruption of the junctional zone. ⁴ The term “junctional zone” was introduced in 1983 to describe a high-signal portion of the uterus at the interface between the low-signal endometrium and the intermediate-signal myometrium on MRI. ⁶ MRI is ideal for distinguishing placenta increta from percreta, as visualization of placental invasion into surrounding tissues is more easily distinguished on MRI than with US. ⁷ Early diagnosis allowing for advanced planning for how to best manage the condition is essential in reducing risks to the patient.

Complications

PAS can cause significant complications during pregnancy, delivery, and postpartum. Women who have had previous cesarean deliveries should consider scheduled cesarean deliveries in subsequent pregnancies, which can help reduce the risk of complications associated with PAS. ⁸ Additionally, early prenatal care and monitoring can help identify and manage any potential complications. The condition increases the risk of postpartum hemorrhage (PPH), which can be life-threatening for both the mother and fetus. Should PAS result in significant maternal hemorrhage, the mortality risk increases 18-fold, with mortality rates as high as 7%, with 90% of patients requiring transfusion and 40% requiring more than 10 units of packed red blood cells (pRBCs). ^{9 10} In one study, the median perioperative blood loss for patients with antenatally confirmed PAS was found to be 3 L. In the same study, 41.7% of those women had an estimated blood loss (EBL) of ≥5 L, and they found no reliable predictors of massive blood loss in women with PAS. ¹¹ One study reported blood loss as high as 17 L requiring 27 units of pRBCs. ¹² Infection is common, with 28% of patients suffering from a postpartum infection with a conservative management approach in which the placenta remains in situ. ⁵ Additionally, PAS has been reported in several case studies as a cause of unscarred uterine rupture, which can even occur in the first trimester. ^{13 14}

Management of Placenta Accreta Spectrum

Conventional Management

With such a high mortality and morbidity, appropriate management of PAS is essential. Peripartum hysterectomy with the placenta left in situ is the standard treatment for PAS disorders, but it has significant rates of morbidity and mortality. ⁵ Standard surgical management involves immediate closure of the uterus following cesarean delivery, while ensuring that the placenta does not spontaneously detach, followed by hysterectomy (commonly known as a c-hyst). It is important to note that forced removal of the placenta is strongly discouraged, as this highly increases the chance of catastrophic hemorrhage. ⁵ Even at large tertiary-care centers, catastrophic hemorrhage can still occur following cesarean hysterectomy. ¹⁵ A cesarian hysterectomy also, of course, results in the end of fertility for the patient. In conservative treatment aimed at preserving the uterus and fertility, a cesarean delivery is performed with the placenta left in situ, sometimes followed by medical management with methotrexate to hasten placental involution. ¹⁶ As this strategy involves retained placenta, this can lead to increased risks of infection, with an additional risk of a delayed-onset hemorrhage. ¹⁷

Role of Interventional Radiology in the Management of PAS

Utilization of interventional radiology (IR) as part of a multidisciplinary approach to manage patients with PAS varies from institution to institution, and may depend on the expertise and experience of the surgical team. Patients with PAS will frequently undergo scheduled cesarian delivery at 34 to 36 weeks, which provides the opportunity for multidisciplinary planning with the IR, obstetrics/gynecology, and possibly the gynecologic oncology teams to best serve the patient with an appropriate treatment plan. If there is high clinical concern for PAS or evidence of PAS on imaging, IR may be included in a multidisciplinary discussion to determine what adjunctive techniques might be appropriate to reduce the risk of catastrophic hemorrhage. Prior to cesarian delivery, arterial balloon occlusion catheters can be placed, with the intent to reduce blood flow to the uterus during hysterectomy, reducing EBL and allowing for a dry surgical field. Uterine artery embolization (UAE) can also be utilized. In situations where these interventions are not performed prior to surgical management, these procedures can both be performed on an emergent basis to limit blood loss.

Interventional Radiology and PAS: Management Techniques

Balloon Occlusion Catheter Placement

Technique and Outcomes

The placement of a balloon occlusion catheter(s) is performed by IR in a variety of settings depending on the management plan and clinical scenario, including in the angiography suite, in a hybrid operating room, with a C-arm or utilizing intravascular US (IVUS) in the operating room, or even in the delivery room in emergent situations. Ideally, arterial occlusion balloon placement is performed by an IR shortly before delivery. Compared to angioplasty balloons, occlusion balloons are softer, more compliant, and therefore less likely to damage vessel walls. Placement of occlusion balloons into the bilateral internal iliac arteries (IIAs) is the most researched, but has shown the least benefit in a recent meta-analysis when compared to occlusion balloon placement in the abdominal aorta (AA) or UAE. ¹⁸ Placement of occlusion balloons into the bilateral IIA is achieved via bilateral common femoral arterial access under fluoroscopic guidance, with occlusion balloons placed over the aortic bifurcation and into the contralateral IIA. The balloon inflation volume required to achieve successful occlusion, as indicated by stasis of contrast distal to the balloon, is recorded. The balloon is then labeled with the volume required for occlusion, and a syringe is attached with a stopcock to the balloon port, to allow inflation when appropriate during the surgery. It is important to secure the balloons and mark them where they exit the sheath to ensure that there is no movement of the balloon prior to surgery, and also to identify cases of inadvertent dislodgement. It is important that movement of the patient be minimized following balloon placement to prevent dislodgement, which makes placement of the balloons while the patient is in the operating room, and possibly already under anesthesia, appealing. The IIA occlusion balloons can then be inflated and deflated as needed during the operation, enabling the surgeons to work in a dry surgical field with control of hemorrhage, and also test whether hemostasis has been successfully achieved with balloon deflation.

In contrast to bilateral IIA balloon placement, AA occlusion balloons require a single, unilateral common femoral arterial access site. Compared to IIA balloons, AA balloons tend to have better outcomes with respect to reduction of EBL. ¹⁹ IVUS can be used in lieu of or in addition to fluoroscopy to place an AA occlusion balloon. This allows more accurate measurement of the vessel diameter to allow for ideal balloon size selection to achieve adequate occlusion. The IR can use IVUS without fluoroscopy to determine appropriate positioning of the balloon by identifying the renal arteries as a landmark and placing the balloon just below the level of the renal arteries ( Fig. 2 ). IVUS placement of AA occlusion balloons is advantageous because ideal sizing and positioning can be achieved without ionizing radiation. In addition, the portable IVUS unit can be utilized in virtually any setting, which means that the patient can be positioned and anesthetized in the ideal operating location for the surgical team. An example from our institution is shown in Fig. 2 , depicting IVUS utilized for an AA balloon placement. This patient was 33 years old and had placenta percreta diagnosed on MRI. Preoperative infrarenal AA occlusion balloon placement was performed by IR using IVUS, which identified a minimum aortic diameter of 15.3 mm. An 8-Fr sheath was placed into the right common femoral artery, and a 16 mm × 4 cm Atlas balloon (Bard Inc, New Providence, NJ) was utilized to achieve occlusion. The balloon was inflated two times for a total of 44 minutes of inflation time during the cesarian hysterectomy. A pulse oximeter on the toe confirmed 100% oxygen saturation following each deflation of the balloon. An EBL of 8 L was observed even with utilization of the AA balloon. An Angio-Seal device (Terumo Interventional Systems, Tokyo, Japan) was used to close the access site.

Fig. 2.

A 33-year-old patient with high suspicion for placenta accreta spectrum. IR was consulted for AA balloon placement prior to cesarian hysterectomy. IVUS was utilized for placement of the AA balloon. ( a–c ) MRI pelvis of the gravid uterus demonstrates evidence of the placenta invading into surrounding organs, including the sigmoid colon (white arrowhead, a ), anterior superior bladder (thin white arrow, b ), and abutting the right internal and external iliac arteries (thick white arrow, c ). ( d ) The renal arteries are shown on IVUS (white arrows). ( e ) The abdominal aorta is measured inferior to the renal arteries using IVUS (green circle); in this case, the abdominal aorta was found to have a minimum diameter of 15.3 mm.

To place an AA balloon occlusion catheter using IVUS or fluoroscopy, access to the right or left common femoral artery is achieved. A guidewire is then advanced into the aorta. A balloon of the appropriate size, as determined by IVUS or fluoroscopy, is advanced over the wire to the infrarenal AA—a balloon approximately 14 mm in diameter is usually appropriate to achieve occlusion. Angiography can be utilized to determine the location of the renal arteries. If utilizing fluoroscopy, the balloon is then inflated, contrast is injected to ensure complete occlusion and lack of contrast passing distal to the balloon, and the volume used and the location of the balloon where it exits the sheath is marked. Should the balloon need to be inflated during surgery, it must be deflated periodically to allow perfusion. An important advantage of AA balloon placement is that it avoids blood flow via collaterals to the surgical field, which can occur with bilateral IIA occlusion. ²⁰ An example of a prophylactic AA occlusion balloon placement at our institution using fluoroscopy is shown in Fig. 3 . In this 37-year-old patient with confirmed placenta accreta, obstetrician scheduled a cesarean hysterectomy at 34 weeks. They assembled a multidisciplinary team including IRs, and planned for AA occlusion balloon placement. During the operation, the balloon was inflated once for a total of 20 minutes. EBL was 1 L. An Angio-Seal device was utilized for arterial access closure.

Fig. 3.

A 37-year-old patient with placenta accrete underwent preoperative abdominal aorta occlusion balloon placement using fluoroscopy. ( a ) The size of the aorta and the location of the renal arteries were confirmed with contrast injection through a 5-Fr flush catheter (white arrowhead) after placement of an 8-Fr vascular sheath. A fetal monitoring device (thick white arrow) is seen overlying the right pelvis. ( b ) A 16 mm × 4 cm Atlas balloon (thin white arrow) was introduced and inflated in the infrarenal AA; contrast injection through the wire port of the balloon confirmed occlusion, with no contrast passing below the level of the balloon.

Data are mixed regarding the benefit of balloon occlusion catheter placement for PAS. In a study of 171 women with morbidly adherent placentas, those who received aortic or iliac artery balloon occlusion prior to hysterectomy had significantly lower EBL (30.9%, p  < 0.001), transfusion requirements (76.8% decrease, p  < 0.001), and ICU admission rates of 0 versus 15.2%, p  < 0.001). ²¹ A recent meta-analysis from 2022 analyzed 20 studies comprising 1,738 patients, and compared balloon occlusion catheters placed in the IIAs, AA balloon occlusion, and UAE. ²² In studies that evaluated outcomes with respect to EBL, 4 favored no peripartum balloon placement, 14 favored prophylactic balloon placement, and 8 of those 14 showed a statistically significant benefit. When comparing balloon occlusion techniques, IIA occlusion had variable results, and was not shown to significantly reduce EBL. ^{20 22 23} AA balloon occlusion was favored for reducing EBL in three studies, and UAE was favored in two studies, which demonstrated a statistically significant benefit. ²² When analyzing all three techniques for their effect on required hysterectomy rates, 6 of 17 studies showed statistically significant decreases in rates of required hysterectomy. ²²

Many obstetrics/gynecology physicians are hesitant to involve IR due to increased costs to the healthcare system, concern for complications, and logistical challenges, even at tertiary-care centers, because their average cesarian hysterectomy EBL at many of these institutions is considered sufficiently safe. However, even experienced gynecology–oncology surgeons will admit that these are very stressful cases, in which aortic compression may become necessary to limit the patient's extensive blood loss, and that there are no reliable indicators of these serious complications. ²⁴ By placing a preoperative AA balloon or utilizing planned UAE, stress could be decreased for surgeons knowing that the risk of catastrophic hemorrhage is potentially mitigated.

Complications

For intra-arterial balloon occlusion catheter placement, complications have been described including arterial thrombosis, dissection, and vessel rupture. Leg ischemia in the context of common or external iliac artery thrombosis or distal embolization is a rare complication. ^{25 26 27 28 29} Thrombectomy (including surgical thromboembolectomy), arterial bypass, or stent placement has been necessary to treat these complications in some cases. ²³ Radiation exposure to the fetus and mother for balloon placement under fluoroscopy should also be considered. Techniques such as limiting frame rate, using a small field of view, limiting magnification use, and limiting oblique fluoroscopy have been shown to minimize the radiation dose. ²³

Uterine Artery Embolization

Technique and Outcomes

UAE immediately prior to or after cesarian delivery in patients with PAS has been utilized to minimize EBL. In the vast majority of patients in whom UAE is utilized, embolization is performed after the cesarian section, but before hysterectomy. In the angiography suite, hybrid operating room, or with a C-arm in the operating room, access to the common femoral artery or left radial artery is obtained. The uterine arteries are accessed using a diagnostic catheter, with or without the use of a microcatheter advanced into the distal horizontal segment of the uterine artery. The uterine arteries are then embolized to stasis using 300- to 700-μm particles, and/or a Gelfoam (Pfizer Inc, New York, NY) slurry. ³⁰ In situations in which the patient is unstable and time is of the essence, the bilateral anterior divisions of the IIAs can also be safely embolized with a Gelfoam slurry to obtain rapid control of the hemorrhage. ^{31 32}

While not typically a favored management strategy, two small studies demonstrated favorable outcomes in patients who underwent UAE immediately prior to delivery. In a prospective study of 69 patients with placental anomalies undergoing UAE on a C-arm using 500- to 700-μm particles prior to cesarian delivery, 52.2% of patients avoided transfusion and 43.5% required hysterectomy. Mean uterine radiation dose of 26.75 mGy was noted. All infants were born with APGAR scores of ≥ 8, and no pH abnormalities were detected in cord blood. All infants had cognitive milestones at 6 months. ³³ In another study, 50 patients with placental anomalies undergoing UAE with Gelfoam slurry an average of 6 minutes prior to cesarian delivery showed that 64% of women avoided transfusion, and 37% of women with diagnosed PAS (10/27) required hysterectomies. All the newborns had APGAR scores of 8 or 9, and normal cognitive function was noted in all 42 infants able to be followed up at 6 months. ³⁰ The mean uterine radiation dose in this study was 15.61 mGy. While these results are promising, it should be noted that there are no data available with respect to long-term outcomes of the infants who underwent UAE prior to cesarian delivery. This technique can also be utilized prior to gravid hysterectomy in a clinical scenario involving PAS prior to planned termination to decrease intraoperative EBL.

UAE after cesarian delivery may be useful in a variety of clinical scenarios, in particular for women hoping to avoid hysterectomy and maintain future fertility. UAE has been shown to increase the speed at which the placenta involutes when left in situ. One study of 12 patients found that UAE led to an average placental resorption of 17 weeks postembolization, compared to 32 weeks on average without UAE. ³⁴ Multidisciplinary discussions may also result in a plan to perform UAE after cesarian delivery, but before hysterectomy, to minimize blood loss. UAE is also an option as an emergent therapy for PPH after delivery and/or surgical management. It should be noted that UAE in patients with PAS can be challenging, given that other arteries in addition to the uterine arteries can supply the placenta, and gravid uteri have a higher degree of vascularity. In a study of 40 women with PAS undergoing emergent UAE, three required a hysterectomy and there was a clinical success rate of 82.5% with three repeat embolizations leading to a 92.5% success rate. PAS was not diagnosed prior to delivery in many of these patients, likely necessitating the emergent nature of the UAE. ³⁵ In a systematic review of 177 women undergoing UAE for PAS, there was an 89% clinical success rate, with 11% requiring hysterectomy. ³⁶

An example of an emergent UAE in a patient with PAS from our institution is shown in Fig. 4 . This is a 34-year-old patient with complete placenta previa and placenta accreta, with a scheduled cesarean hysterectomy performed at 34 weeks of gestation. During the procedure, manual placenta extraction was performed, and the placental bed in the endometrium was noted to be bleeding briskly. Sutures and the Bakri balloon were placed to control the hemorrhage, and IR was emergently consulted. A 14-mm Atlas balloon was placed in the AA in the operating room, which was insufflated in 10-minute increments with 1-minute deflations in between during the initial portion of the hysterectomy. The patient was then brought to the IR suite for bilateral UAE due to persistent uncontrolled bleeding. Angiography demonstrated prominent uterine arteries and vascularity consistent with gravid uterus, with pooling particularly near the fundus of the uterus suggestive of active extravasation. Both uterine arteries were successfully embolized with Gelfoam slurry to stasis via a microcatheter. The patient overall had 6 L of EBL and required 16 units of pRBC. This case illustrates how quickly hemorrhage can become uncontrolled, and why consultation with IR prior to delivery could be beneficial to optimize management in these high-risk clinical scenarios.

Fig. 4.

A 35-year-old patient with history of focal placenta accreta and placenta previa, who experienced massive hemorrhage following cesarian section. Arterial ( a, c ) and delayed ( b, d ) digital subtraction images from internal iliac angiography in two dimensions demonstrate multiple foci of active extravasation arising from the distal uterine arteries (white arrows). The bilateral uterine arteries were subsequently embolized to stasis using a Gelfoam slurry.

Complications

Complications of UAE include arterial dissection, pseudoaneurysm, nontarget embolization, access site hematoma, loss of fertility, and infection. ³⁷ With respect to fertility, one retrospective study of women with PAS who underwent preservative cesarean delivery with ( n  = 49) or without ( n  = 139) UAE who completed long-term follow-up showed no difference in the rate of abortions, pregnancies, or deliveries between groups, and similar rates of PAS in future pregnancies. ³⁸ Interestingly, a recent systemic review compared 483 pregnancies with prior UAE for PPH to 320,703 pregnancies without prior UAE. Using a patient background-matched analysis based on previous PPH, the analysis showed that prior patients with prior PPH and UAE had higher rates of developing future PAS (odds ratio [OR]: 20.82; 95% confidence interval [CI]: 3.27–132.41) and PPH (OR: 5.32, 95% CI: 1.40–20.16) in future pregnancies, but not higher rates of hysterectomy (OR: 8.93, 95% CI: 0.43–187.06) or other complications such as placenta previa, fetal growth restriction, or preterm birth compared with those who did not undergo prior UAE. ³⁹ Ultimately, further research is necessary to determine long-term effects of UAE on future fertility in the setting of PAS; however, embolization is effective in controlling severe hemorrhage in PAS, which poses high risks of morbidity and mortality to patients. These results highlight the need for multidisciplinary discussion that involves the patient to create an individualized plan of care.

Conclusion

Involvement of IR as part of a multidisciplinary approach to manage patients with PAS varies significantly from institution to institution. With a high rate of morbidity and mortality, and up to 50% of patients with PAS experiencing PPH, it is the authors' opinion that involving IR in the conversation early and often can only have a positive impact on patient outcomes. While the procedures offered by IR are not without complications, AA balloon placement and UAE have both been convincingly shown to be effective at reducing transfusion, EBL, and required hysterectomy rates. ²³ IR procedures may also help preserve the patient's fertility by aiding in placental involution. Opportunity exists for IR to become more involved in the early care of PAS patients to avoid emergent interventions and complications of catastrophic hemorrhage in these high-risk patients.