Interventional Radiology in Pregnancy Complications: Indications, Technique, and Methods for Minimizing Radiation Exposure

LEARNING OBJECTIVES

After completing this journal-based CME activity, participants will be able to:

•.	List the complications of pregnancy that may be treated with interventional radiology procedures.
•.	Describe the interventional radiology techniques used to treat ante- and postpartum complications of pregnancy.
•.	Minimize the amount of radiation to which patients are exposed during ante- and postpartum interventional procedures.

Introduction

The process of pregnancy depends on the fulfillment of numerous physiologic steps, from conception to childbirth, within a given anatomic context. A misstep or an anatomic variant may result in a complication that manifests in either the antepartum or the postpartum period. Because the gestation process is complex and many advanced imaging techniques are available for monitoring it, the role of the radiologist has become increasingly important in the expeditious and accurate diagnosis of any complications. Antepartum complications that are amenable to imaging-based diagnosis and imaging-guided treatment include ectopic pregnancy, symptomatic ovarian cyst, and obstructive nephrolithiasis; their postpartum counterparts include hemorrhage, abscess after cesarean section, and vesicouterine fistula.

Complications of pregnancy that have gynecologic as well as obstetric implications have been managed conventionally with surgery. However, surgical management is associated with short-term risks of maternal and, occasionally, fetal morbidity and mortality, as well as a long-term risk of loss of maternal fertility. Consequently, the interventional radiologist, with an armamentarium of therapeutic options that obviate surgery, is playing a growing role in the management of such complications.

However, the prospect of imaging-guided intervention may produce unease among patients and clinicians and in the general public. Increased general awareness of the risks of radiation exposure over time, combined with the relative youth of most pregnant women and the vulnerability of the fetus, makes it imperative that interventional radiology procedures be performed with forethought and care to minimize the radiation levels to which the patient is exposed. In the absence of definitive data about the health effects of radiation doses delivered by specific diagnostic imaging protocols, the National Council on Radiation Protection has advised that exposure be kept as low as reasonably achievable, a guideline widely referred to as the ALARA principle.

The article describes the interventional radiology procedures that are used to treat various complications of pregnancy. Such procedures include direct chemical injection of an ectopic gestational sac, uterine artery embolization (UAE) for postpartum hemorrhage, aspiration of a symptomatic ovarian cyst, drainage of a post–cesarean section abscess, percutaneous nephrostomy for obstructive hydronephrosis, and suprapubic cystostomy for a postpartum vesicouterine fistula. Some of these procedures involve the use of ultrasonography (US) for guidance and thus arouse no concern about ionizing radiation. In other procedures, fluoroscopy or computed tomography (CT) is used. The article summarizes the data available about typical maternal and fetal radiation doses resulting from the use of CT and describes methods that may be used to minimize the amount of ionizing radiation to which pregnant patients are exposed.

Fetal Radiation Exposure

Health Implications

According to the National Council on Radiation Protection and Measurements, the risk to a fetus from diagnostic imaging is significantly increased when the radiation exposure exceeds 150 mGy (1,2). Yet, at doses of less than 50 mGy, the risk for radiation-induced abnormality is considered negligible in comparison with baseline risks for all developmental abnormalities (eg, 1% for mental retardation, 3% for spontaneous birth defect) (1,3). Teratogenesis, a deterministic effect of radiation, is absent below a specific threshold radiation level; above that threshold, its severity depends on the gestational age of the fetus at the time of exposure. (Threshold radiation doses for deterministic effects are estimated on the basis of data from studies among Japanese survivors of World War II nuclear bomb attacks and in patients undergoing radiation therapy [1].) However, carcinogenesis is a stochastic effect of radiation, and there is no threshold below which the risk of cancer is eliminated. Although no definitive data exist about the carcinogenic effects of radiation delivered during diagnostic and interventional radiology procedures, epidemiologic data support the hypothesis that the risk for cancer is increased among children exposed to ionizing radiation during gestation (1,4,5). However, estimates of the frequency of childhood cancers resulting from radiologic imaging exceed the frequency of documented cancers in the children of Japanese nuclear bomb survivors (1,4).

Maneuvers for Minimizing Dose

Using data derived from the literature (6–9) and radiation dose records from our institution, we have summarized typical radiation exposure levels during the specific procedures discussed in this article (Table).

US should be used for guidance of interventional procedures whenever possible. When it is necessary to use fluoroscopy, special attention must be given to radiation-sparing maneuvers. Methods for reducing fetal radiation exposure include (a) placement of lead aprons between the patient and the table, (b) minimizing fluoroscopy time, (c) using magnification only when necessary, (d) performing pulsed fluoroscopy at the lowest pulse rate that provides sufficient image quality, (e) maximizing the distance between the x-ray source and the receptor, (f) minimizing the distance between the patient and the receptor, (g) using collimators, and (h) decreasing the number of images acquired during digital subtraction angiography and cinematic acquisitions (10,11). Monitoring and recording of radiation exposures is important to enable future assessment of possible effects on the fetus. Measures of radiation exposure may include estimates of peak skin dose, reference point air kerma, kerma-area product, or, if these are unavailable, fluoroscopy time. These data should be included in the patient's medical record or the procedure report (10).

In CT-guided drainage procedures, methods that may be used to reduce the amount of radiation to which the patient is exposed include (a) using a low tube current–time product for all acquisitions after the preliminary scan, (b) limiting the length of the scanned body area to the minimum needed to provide sufficient guidance for the procedure, (c) minimizing the number of acquisitions, (d) increasing the pitch, and (e) using a “quick-check” technique instead of a “real-time” technique when performing CT fluoroscopy (10). Current CT scanners automatically calculate and record the dose-length product, a measure that should be recorded in the examination report and included in the general medical record to allow estimation of the fetal radiation dose.

Ectopic Pregnancy

As many as 2% of pregnancies among women in the general population and 4.5% of pregnancies among women who undergo fertility treatments are ectopic (12,13). The incidence of ectopic pregnancy has risen in the past few decades, but the associated mortality (previously as high as 5%) has decreased, likely because technical advances in laboratory testing and clinical imaging have enabled diagnosis at an earlier stage (13,14). The most common location of an ectopic pregnancy is the fallopian tube (>90% of cases), followed by the cornu (2%–4%), cervix (1%), cesarean section scar, ovary, and abdomen. Heterotopic pregnancy (ie, simultaneous intrauterine and ectopic implantations), although rare in the general population, occurs in 1%–3% of women who undergo fertility treatments (12).

Conventional Therapy

Management options for ectopic pregnancy include surgery, medical therapy, and short-interval surveillance (12). Laparotomy and laparoscopy previously were mainstays of therapy; now, small intact ectopic implantations detected at an early stage are often managed conservatively. However, evidence of hemodynamic instability or sac rupture (eg, hemoperitoneum) are indications for surgery. Expectant management is generally reserved for patients with a nonviable tubal implantation and a low or downward-trending serum level of beta human chorionic gonadotropin (β-hCG) (14,15).

Medical management of a tubal pregnancy typically involves systemic administration of methotrexate, a folate antagonist, which can be administered as a single intramuscular injection at a dose of 50 mg/m² (12,16). The serum level of β-hCG is measured on days 4 and 7 after the injection; if there a reduction of at least 15% in the β-hCG level, there is a high likelihood that the ectopic pregnancy will resolve spontaneously (12). Absence of such a reduction is an indication for repeat intramuscular injection of methotrexate on day 7, followed by a repeat assessment of the β-hCG level. A continued lack of reduction in the level of β-hCG or evidence of sac rupture may prompt alternative therapy. Factors associated with treatment failure include the presence of fetal cardiac activity, a serum β-hCG level higher than 4000 mIU/mL, and a sac diameter of more than 3.5 cm (12,17,18).

In patients in whom systemic methotrexate therapy is predicted to fail or has failed or who have heterotopic pregnancies with an intrauterine implantation that they wish to retain, other conservative, fertility-preserving management options become important. Interventional radiology procedures constitute the core of conservative management in these cases.

Imaging-guided Therapy

Tubal Pregnancy.—In cases of tubal pregnancy, US-guided direct chemical injection of the ectopic implant is an important alternative to surgery. After antibiotic prophlyaxis is administered and the vaginal vault is cleansed with preparatory solution, a needle (eg, 20-gauge Chiba type) is inserted with transvaginal US guidance into the amniotic sac. An electronic needle guide is typically used to facilitate planning of the needle route, and color Doppler imaging helps verify the absence of vessels along that route. Typically, the amniotic fluid is aspirated first, and a chemical is then injected into the sac. Aspiration is performed first (a) to mechanically disrupt the sac and (b) to prevent overdistention of the sac and leakage of the chemical during injection. Common chemicals that may be injected include methotrexate (1 mg per kilogram of body weight), potassium chloride (1–3 mL in a 2 mEq/mL solution), and hyperosmolar glucose (50% solution) (12,19).

Potential advantages of injecting methotrexate directly into the amniotic sac are a higher local concentration of the chemical and a lower risk of systemic toxic effects (19). Potassium chloride or another chemical solution other than methotrexate may be used to allow retention of the intrauterine implant in women with heterotopic pregnancies or in women with severe pulmonary disease, blood dyscrasia, or another contraindication to methotrexate therapy (19). In women with a viable tubal pregnancy indicated by fetal cardiac activity, the injection of potassium chloride may be preferred to increase the probability of cessation of cardiac activity. Follow-up after direct chemical injection of an ectopic sac is similar to that after intramuscular injection of methotrexate.

The primary contraindications to direct injection of an ectopic sac are hemodynamic instability and hemoperitoneum, which are typically considered indications for immediate surgery (12). In addition, because of the importance of follow-up testing of the serum level of β-HCG, patients who are likely to be lost to follow-up may not be good candidates for this alternative therapy.

Ectopic Pregnancy in Other Sites.—Direct chemical injection is also a potentially effective therapy for an ectopic sac implanted in the cornu, cervix, or cesarean section scar (20–22). The technique used is similar to that for injection of a tubal ectopic sac. However, because the sac in a cornual ectopic pregnancy may be larger than that in a tubal pregnancy and because the surrounding tissue is more vascular, some interventional radiologists perform UAE immediately before a cornual sac injection to reduce the risk of postinjection hemorrhage. Some authors also have reported the use of UAE in conjunction with intramuscular methotrexate therapy, or after failed methotrexate therapy, for the successful treatment of cornual and cervical ectopic pregnancies (18,23,24). Embolization agents used in UAE include absorbable gelatin sponge and polyvinyl alcohol (PVA) particles (20).

In a cervical pregnancy, because the surrounding tissue is fibrous and subject to severe intraoperative or postoperative hemorrhage, a direct sac injection may be immediately preceded by bilateral uterine artery occlusion (Fig 1) (12). Uterine artery occlusion is performed by inflating the ballon tip of a catheter that has been inserted into the common femoral artery and passed through the internal iliac artery to the origin of the uterine artery.

With the increasing frequency of delivery by cesarean section and ongoing improvement in diagnostic imaging techniques, ectopic pregnancies along cesarean section scars are more frequently found within the first trimester. US-guided direct injection of the sac has been shown to be an effective treatment for ectopic pregnancies in this location, with reported success rates of 71% to 80% (22). To reduce the risk of hemorrhage before direct sac injection or intramuscular injection of methotrexate (Fig 2), bilateral UAE or bilateral uterine artery occlusion may be performed.

During interventional radiology procedures that involve arterial embolization or occlusion, close attention must be given to minimizing the amount of radiation to which the mother and fetus are exposed during fluoroscopy. The use of collimators, pulsed acquisitions, and limited total exposure time, along with the avoidance or minimal use of magnification and the minimization of the number of images acquired with digital subtraction angiography, can help achieve this goal.

Strict follow-up of serum β-hCG levels, as described earlier, is important to allow timely identification of treatment failure and selection of an alternative management strategy, such as surgery. Although all patients who undergo therapy for an ectopic pregnancy are generally advised about the risk of loss of fertility, those who undergo direct sac injection and UAE have been shown to have lower morbidity and a shorter average hospital stay than those who undergo surgical treatment, and some of them have subsequently become pregnant (14,18,25).

Postpartum Hemorrhage

Pathogenesis and Diagnosis

Postpartum hemorrhage is an obstetric emergency that may occur after vaginal delivery or cesarean section. It complicates as many as 5% of deliveries, has an associated mortality of 1%, and is a major indication for urgent hysterectomy (26–29). Postpartum hemorrhage is formally defined as blood loss that exceeds 500 mL after vaginal delivery or 1000 mL after cesarean section (27). However, estimates of the volume of blood lost are unreliable, and a more clinically relevant definition might be a postpartum blood loss that produces symptoms of dizziness or hemodynamic instability (27).

Primary postpartum hemorrhage is defined as bleeding that occurs in the first 24 hours after delivery. Most cases of postpartum hemorrhage are a result of uterine atony (Fig 3), a condition that has been implicated in as many as 80% of cases (30,31). Other important causes include retained products of conception, coagulopathy, trauma (eg, vaginal or uterine laceration), placenta accreta, placental abruption, and uterine arteriovenous malformation (AVM) (30,32,33).

It is noteworthy that not all postpartum hemorrhages are manifested by vaginal bleeding: An intraabdominal hemorrhage may occur without any visible emission of blood (Fig 4). Thus, diagnostic CT may be indicated for a postpartum patient with signs of blood loss but absent or mild vaginal bleeding.

Secondary postpartum hemorrhage is defined as bleeding that occurs from 24 hours to 12 weeks after delivery (34). Bleeding is typically less massive than that resulting from primary postpartum hemorrhage and may be due to uterine atony, retained products of conception, endometrial inflammation or infection, or uterine AVM or pseudoaneurysm (34,35).

Prenatal diagnosis of placenta accreta is important to obviate emergent management during delivery. US findings include placenta previa, a placental lacuna that may demonstrate turbulent color flow, and loss of the normal retroplacental clear space (36). A myometrial thickness of less than 1 mm also may be seen. MR findings may include placenta previa, uterine bulging, placental bands that appear hypointense on T2-weighted images, focal interruptions in the myometrial wall, and heterogeneous placental signal intensity (36).

To avoid massive hemorrhage from surgical instrumentation during delivery, awareness of a uterine AVM is critically important. US findings of a uterine AVM include myometrial vascular lakes with low impedance, high diastolic flow, and color aliasing on duplex US images (37). MR imaging also may be helpful, with characteristic findings of serpiginous myometrial signal voids on spin-echo images (37).

Conventional Therapy

Management of a postpartum hemorrhage depends on the mode of delivery and the severity of the hemorrhage. After vaginal delivery, medical management is often the frontline therapy, and includes fundal massage, uterotonic agents (eg, oxytocin, methylergonovine), intravenous hydration, and transfusion of blood products (27). Inspection of the birth canal is important to exclude lacerations. Vaginal or uterine packing or uterine balloon tamponade may be used (30,38). Surgical intervention (eg, uterine artery ligation or placement of uterine compression sutures) may be necessary in cases of medically refractory postpartum hemorrhage (30). Hemostatic hysterectomy is generally a measure of last resort but should be performed without delay in the critically unstable patient, although it is associated with high morbidity and mortality as well as loss of fertility (39).

In cases of postpartum hemorrhage after cesarean delivery, surgical intervention (eg, evacuation of products of conception, bilateral uterine or internal iliac artery ligation, or placement of uterine compression sutures) may be preferable while the abdomen is exposed (30). Management of a postpartum hemorrhage that occurs after the abdomen is closed is generally similar to that of hemorrhage after vaginal delivery.

Imaging-guided Therapy

Uterine Atony or Arterial Laceration.—UAE or internal iliac artery embolization (Figs 3, 4) is an important nonsurgical management option offered by interventional radiologists for the treatment of medically refractory postpartum hemorrhage. It may be performed in a hemodynamically stable patient with refractory postpartum hemorrhage or in a hemodynamically unstable patient in whom surgical management has failed or for whom surgery is considered too risky. The procedure begins with diagnostic angiography to detect vascular abnormalities such as extravasation (Fig 4), pseudoaneurysm, arterial truncation, or AVM. However, the lack of visualization of a vascular abnormality does not necessarily preclude embolization in a patient with postpartum hemorrhage, as angiographic demonstration of extravasation requires a minimum flow rate of 0.3–1.0 mL/sec (27).

In general, if the uterine arteries are accessible and patent, embolization with a slurry of absorbable gelatin sponge may be performed bilaterally. Occlusion is temporary because the gelatin sponge is absorbed by the tissues after several weeks (40); however, a transient occlusion generally suffices to achieve hemostasis. Some interventional radiologists may opt to use PVA particles, which provide permanent occlusion. The use of metallic coils also may be considered, particularly in the presence of a large vessel laceration (27). Gelatin sponge or PVA particles are usually mixed with contrast material and injected through a selective catheter or coaxial microcatheter system positioned within the uterine artery until stasis of flow (a static column of contrast material that persists over several arterial pulsations) is visualized (27). Iliac arteriography is repeated after embolization to detect bleeding from other vessels (eg, the internal pudendal artery), which may become apparent only after UAE (27).

In some patients (eg, those with previous uterine artery ligation or hysterectomy), UAE is impossible or ineffective. In such cases, bilateral internal iliac artery embolization may be performed. If postpartum hemorrhage persists after ligation of the anterior division of the internal iliac arteries, angiography may be performed to search for other sources of bleeding. Anastomoses between uterine arteries and other vessels may be implicated in patients with refractory postpartum hemorrhage after arterial ligation or embolization; in such cases, successful cessation of bleeding has been described after embolization of ovarian, medial circumflex, and inferior epigastric arteries (27,41,42). Bilateral internal iliac artery embolization also may be performed, regardless of the accessibility of the uterine arteries, if the patient is hemodynamically unstable and expeditious therapy is required (27).

Reported clinical success rates for arterial embolization in the setting of postpartum hemorrhage range from 79% to 97% (27,43–45). Kirby et al (27) found that success did not seem to depend on the mode of delivery (whether vaginal or by cesarean section), transfusion requirements, cause of postpartum hemorrhage, or time from delivery to embolization. However, active extravasation demonstrated at angiography during a first attempt at embolization was associated with a lower success rate (27). When an initial attempt at embolization fails, a second embolization attempt is often worthwhile; a success rate of 80% was reported after repeat embolization for cessation of postpartum hemorrhage (27).

Arterial embolization is associated with significantly reduced morbidity compared with that after surgery (43,44). The most common complication is postembolization syndrome, which is self-limited (27). Unintended embolization of the posterior division of the internal iliac artery, or less often, the external iliac artery, may occur. Rarely, vascular perforation and end-organ (eg, uterus, bladder) ischemia may be encountered (27). It is important to note that menstrual function and fertility are preserved in many women after UAE, without any associated increase in adverse events in subsequent pregnancies (46).

Placenta Accreta.—Placenta accreta (Fig 5) is defined as abnormal attachment of chorionic villi to the myometrium because of a defect in the decidua basalis (36). Risk factors include previous cesarean section and placenta previa. Placenta increta refers to a more severe form in which villi invade the myometrium, and placenta percreta refers to extension of villi to the uterine serosa and sometimes the surrounding organs.

With the increasing number of deliveries by cesarean section over the past few decades, an increase in the incidence of placenta accreta has been observed. This condition is now the most common indication for emergent postpartum hysterectomy (36). Possible postoperative complications of emergent hysterectomy include massive life-threatening hemorrhage.

In general, delivery is performed by cesarean section at a gestational age of 36 weeks to avoid the risks of spontaneous labor (48). Before delivery, bilateral internal iliac artery balloon occlusion is performed to reduce the risk of hemorrhage and maintain a clear surgical field (49). The balloon on both catheters may be inflated intermittently during the surgical procedure or may be left inflated if excessive bleeding occurs. As a precaution, the catheters (with balloons deflated) may be left in place for a short period after surgery, to expedite angiography and embolization in cases of postpartum hemorrhage.

Arterial embolization is another strategy for prevention of postpartum hemorrhage in patients with placenta accreta. In one variant of the procedure, the patient is brought to the angiography suite for placement of bilateral femoral vascular sheaths (40). The patient is then transferred to the operating room for cesarean delivery, which may be followed by a partial evacuation of the placenta. The patient is then transferred back to the angiography suite for bilateral UAE with absorbable gelatin sponge or PVA particles, as described previously. The remaining placenta is then allowed to evacuate spontaneously over the ensuing months (40). Hemorrhage during that time is rare and may be successfully treated with repeat UAE (40).

The interventional radiologist also plays a critical role in the emergent management of patients with placenta accreta (Fig 5). Because postpartum hemorrhage may be severe in these patients, medical management may be insufficient, and arterial embolization may be needed if immediate surgical management is not required (40).

The mother and fetus are exposed to substantial amounts of radiation during angiographically guided treatment of placenta accreta; therefore, the use of the radiation-sparing maneuvers described earlier is critical. Radiation monitoring with dose documentation in the medical record or the procedure report is important to help address potential future concerns regarding such exposures (10).

Uterine AVMs.—Uterine AVMs are a rare cause of postpartum hemorrhage. AVMs are tangles of variable-sized vessels, including feeding arteries and draining veins, without an intervening capillary network (37). Congenital uterine AVMs typically extend beyond the uterus and involve multiple pelvic feeding arteries and draining veins; they are rarely confined to the uterus (37). By contrast, acquired uterine AVMs (Fig 6) are almost always confined to the uterus. Risk factors for acquired uterine AVMs include gestational trophoblastic disease, previous instrumentation (eg, dilation and curettage), or diethylstilbestrol exposure (37).

Although hysterectomy is the definitive treatment option for bleeding AVMs confined to the uterus, arterial embolization can be an effective and safe therapeutic option when preservation of the uterus is desired (37,45). Preserved menstrual function and subsequent pregnancy have been described after embolization of uterine AVMs (50). The embolization procedure begins with unilateral internal iliac arteriography, which is performed by inserting a 4–5-F vascular sheath through either the left or the right common femoral artery to the internal iliac artery. Access to the uterine artery is achieved with a selective catheter or microcatheter. The separate and combined use of various embolic agents, including N-butyl cyanoacrylate glue, PVA particles, metallic coils, and absorbable gelatin sponge (Fig 6), has been described; the choice of embolic agent is typically dependent on operator preference and expertise (37). Occlusion of the AVM nidus may be performed with glue. If access to the nidus is difficult, coil embolization of the feeding arteries or nonselective embolization of the uterine arteries may be performed by using PVA particles, absorbable gelatin sponge, or both.

When N-butyl cyanoacrylate glue is used, it is admixed with an iodinated contrast material (Lipiodol Ultra-Fluide; Guerbet, Bloomington, Ind) (37). Arteriovenous transit time is assessed at preembolization arteriography to determine the appropriate proportions of glue and lipiodol; a nidus with a short transit time may be more effectively embolized by using a higher proportion of glue in the composite to achieve more rapid polymerization (37). Postembolization pelvic angiography is important to exclude accessory feeding vessels. The success rate of embolization for the control of bleeding is reported to be as high as 93%–96%, although repeat embolization sometimes is needed (37,51). The median time interval between initial embolization and repeat embolization in one series was 16 months (37).

Symptomatic Ovarian Cyst

Large ovarian cysts occasionally cause pain or pressure in both pregnant and nonpregnant patients. Although such cysts can be removed surgically, risks to the mother and fetus from surgery during pregnancy make this option undesirable (52). Rates of fetal loss after ovarian cystectomy may be as high as 18%–25% (52).

In contrast, complex cysts should not be treated with aspiration; instead, the patient should be evaluated clinically and, on occasion, with additional imaging to exclude the possibility of malignancy. Patients with acute pain should generally undergo evaluation for ovarian torsion, which should be excluded before aspiration of the cyst contents is performed (54).

The procedure may be performed with a sedative such as fentanyl citrate or without sedation. Preliminary gray-scale US is performed to visualize the cyst and confirm the absence of complex elements suggestive of malignancy, and Doppler US may be used to assess any intervening vessels along the planned route of needle insertion. If transvaginal US is used for guidance, a 20-gauge Chiba-type needle is attached to the needle guide of the endovaginal probe (55). With real-time US guidance, the needle is inserted into the cyst and aspiration is performed. The needle is removed after collapse of the cyst is demonstrated at US. The aspirate is typically submitted for cytologic evaluation. Aspiration may have to be repeated, as cyst recurrence is not unusual. The procedure is generally well tolerated and is not associated with major complications (56).

Post–Cesarean Section Abscess

Puerperal infections are fairly common. Antibiotics are the mainstay of therapy for postpartum endometritis; however, a fever that persists after 48–72 hours of antibiotic therapy may be a sign of a different source of infection. Because anatomic boundaries are disrupted during cesarean delivery, a persistent fever despite intravenous antibiotic therapy may prompt a diagnostic work-up for post–cesarean section fluid collection. CT is the mainstay of imaging evaluation in such cases. Postoperative collections after cesarean delivery may be found in the abdomen, pelvis, psoas musculature, or ventral abdominal wall (57,58). Occasionally, uterine incisional necrosis or dehiscence is encountered, in which case surgery may be unavoidable. However, imaging-guided drainage is the preferred treatment choice in most instances.

Transabdominal percutaneous drainage may be performed with US or CT for guidance (Figs 8, 9). US is generally preferred if it allows adequate visualization of the entire abscess cavity, because it involves no ionizing radiation, requires less time, enables real-time guidance, and allows more flexible access of a collection from multiple angles. CT may be necessary for transabdominal drainage if the targeted collection is not visible with US or is obscured by overlying structures such as bowel. Drainage (Fig 8) may be performed by using a direct trocar technique, in which a catheter loaded onto a sharp stylet is advanced directly into the collection during US visualization (54). Alternatively, the Seldinger technique may be used (59) with limited fluoroscopic guidance for manipulation of the wire.

Some pelvic collections may not be amenable to transabdominal drainage; the bladder, vessels, bowel, or bone may obscure the target. In such cases, when transgluteal access is possible, CT-guided transgluteal drainage is a safe and effective alternative. In general, a catheter path is chosen that is as close to the sacrococcygeal margin as possible and inferior to the piriformis muscle to avoid injuring the sciatic nerve and gluteal vessels and to minimize the risk of pain and bleeding (60). A tandem trocar or Seldinger technique may be used.

Occasionally, a pelvic collection may be inaccessible by either a transabdominal or a transgluteal route. US-guided transvaginal drainage is safe and effective and may be performed in such cases (55). Transvaginal drains are generally well tolerated but may be more prone to dislodgment in comparison with transabdominal and transgluteal drains.

Percutaneous drainage enables decompression of the abscess cavity, allowing the walls of the cavity to adhere. In conjunction with drainage, antibiotic therapy is important and is tailored to treat microorganisms that have been cultured from specimens submitted at the time of drainage. Some collections may represent superinfected hematomas (61). In addition, bladder or ureteral injury as a complication of cesarean delivery may result in a urinoma; in some cases, urinary diversion may be necessary in conjunction with drainage of the urinoma at percutaneous nephrostomy (62).

When CT is used for guidance, several maneuvers may be used to minimize maternal radiation exposures. These include performing fewer scans and decreasing the number of sections acquired per scan of the targeted body area, using a lower tube current, and employing a “quick-check” technique for CT fluoroscopy (10).

Obstructive Uropathy

Obstructive ureterolithiasis occurs in one of 200–1500 pregnant woman (63). More than 80% of cases occur in the second and third trimesters, with equal incidence in the right and left collecting systems (63,64). US is the mainstay of the imaging-based diagnosis of obstructive uropathy, with findings of renal or ureteral stone, hydronephrosis, and hydroureter considered indicative of the condition (64). In addition, the unilateral absence of a ureteral jet at color Doppler imaging is suggestive of a unilateral ureteral obstruction; this finding may be confirmed by repeating the examination with the patient in the contralateral decubitus position to reduce ureteral compression by the gravid uterus (65). When ureterolithiasis is suspected but not identified at abdominal US, transvaginal US may be performed for better visualization of the distal ureters (66). In general, CT is avoided because of radiation. MR urography may be helpful for problem solving but is limited in that it cannot provide direct visualization of the stone (67).

Management is conservative; in as many as 80% of patients, the obstruction resolves with hydration, bed rest, and analgesia (63). However, when conservative therapy fails, symptomatic obstruction in the pregnant patient may require action. Currently, the definitive therapy is ureteroscopic removal of stones. However, contraindications to ureteroscopic removal include infection or sepsis, large stone burden (sum of maximum diameters, >1 cm), and lack of the requisite equipment and experience (63).

Percutaneous nephrostomy is a temporizing measure that may serve as a bridge to ureteroscopy, ureteral stent placement, or spontaneous passage of stones, allowing deferral of definitive therapy until after delivery (64). In one patient series that included both pregnant and nonpregnant women, the technical and clinical success of percutaneous nephrostomy was 100% (68). However, when performing the procedure in a pregnant woman, there are special challenges, including (a) the impossibility of positioning the patient in the standard (prone) position and (b) the desire to limit fetal radiation exposure from fluoroscopy.

Percutaneous nephrostomy may be performed in a pregnant patient by using an oblique prone position with US for guidance (Fig 10) (64). If difficulty is encountered in US visualization or wire manipulation, limited fluoroscopy, with appropriate maneuvers to limit fetal radiation as outlined previously, can be used (Fig 11). A 21- or 22-gauge needle is advanced into a selected calyx with US guidance. Removal of the needle stylet may allow urine to be aspirated; subsequently, an 0.018-inch wire is advanced into the collecting system. The needle is then removed, and a 5- or 6-French dilator-sheath assembly is advanced into the collecting system. The dilator is removed, and the 0.018-inch wire is exchanged for a 0.035-inch (3-mm) J-tip wire. The sheath is then exchanged for an 8-F nephrostomy tube. Percutaneous nephrostomy in pregnant patients has been performed during intravenous sedation with opiates and with local anesthesia alone.

Possible complications of the procedure include septic shock in the setting of urosepsis, as well as hematuria; major hemorrhage is rare (67). Other complications include tube dislodgment and tube obstruction (67).

Vesicouterine Fistula

Vesicouterine fistula is a rare entity with an increasing incidence because of the increasing frequency of cesarean sections, particularly lower segment cesarean sections (48,69). It is more common after repeat cesarean section but may also occur after a forceps- or vacuum-assisted vaginal delivery following a cesarean section. Abnormal communication between the bladder and uterus may be demonstrated at cystography or hysterography (48). Transvaginal US may demonstrate a hypoechoic line between the anterior uterine wall and bladder, although larger fistulas may be obviously anechoic (48,70). At MR imaging, the fistula may be identified on heavily T2 weighted images (61). Vesicouterine fistulas also have been identified at CT cystography (Fig 12) and hysterography (48).

As many as 5% of vesicouterine fistulas may close spontaneously, with involution of the puerperal uterus. If the fistula is discovered soon after delivery, conservative management with catheter decompression for 4–8 weeks may allow fistula healing and hence obviate surgery. Although transurethral placement of a Foley catheter may be used for decompression (71), long-term transurethral catheterization may be inconvenient and uncomfortable for the patient. Placement of a percutaneous suprapubic cystostomy tube is an alternative in such cases and may be performed by using the Seldinger technique (with either US alone or combined US and fluoroscopy for guidance) (Fig 12) or the direct trocar technique (72). Use of the Seldinger technique may result in higher radiation exposure because fluoroscopy is needed for guidance of wire manipulation, whereas fluoroscopy is unnecessary or limited when the trocar technique is used. Follow-up contrast material injection of the cystostomy tube may be performed to help confirm fistula closure when clinical symptoms have resolved. If a vesicouterine fistula persists, surgical repair may be necessary.

Conclusions

Knowledge of imaging findings of pregnancy complications is critical to their diagnosis and timely management. Interventional radiologists can provide effective management options in a variety of pregnancy complications, in some cases obviating surgery, minimizing morbidity, and potentially preserving fertility. In critically ill patients, however, surgical management should not be delayed if surgery is the definitive treatment. When fluoroscopy or CT is used for procedural guidance, attention to radiation-sparing maneuvers is encouraged to reduce fetal and maternal exposures. Intraprocedural radiation monitoring and dose documentation are important, particularly when future review of fetal exposures will be performed by the patient and physician team.