Just wanted to put it in a way that I could understand the stuff.
A 30-year-old gravida 3, para 2 patient who is 23 weeks pregnant presents to the maternal-fetal medicine department. She was referred to the maternal-fetal medicine department at the request of her primary obstetrician following an obstetric ultrasound that demonstrated complete placenta previa. The patient has a history of 2 prior pregnancies complicated by complete placenta previa. Both prior pregnancies were delivered by low transverse cesarean sections (LTCS). The patient has no other previous surgical history or significant past medical history. She has no known allergies and is not currently taking medications. She does not report any vaginal bleeding. She has no abdominal pain, cramps, or contractions. Quickening was first noted at 19 weeks and she continues to feel regular fetal movement. She denies having any vaginal discharge or leakage of fluid. She has no other complaints.
The patient is well-appearing on physical examination. Her blood pressure is 90/60 mm Hg and her heart rate is 90 bpm. She has normal respirations at a rate of 12 breaths/min, with an oxygen saturation of 96% while breathing room air and a tympanically obtained temperature of 99°F (37.2°C). She weighs 165 lb (74.8 kg) and has a body mass index (BMI) of 28.3. The cardiovascular and respiratory examinations are unremarkable. The abdomen is gravid, with a fundal height of 24 cm. She has positive bowel sounds in 4 quadrants and no tenderness to palpation. No peripheral edema or rash is present.
The patient is blood type A-positive, with a negative antibody screen. Additionally, the rapid plasma reagent (RPR) examination is nonreactive for syphilis, and the hepatitis B surface antigen test is negative. A diabetes screen is normal at 23.4 weeks (however, this is typically done at 26-28 weeks). Her antibody screen is negative. Her complete blood cell count (CBC) demonstrates a hemoglobin of 14 g/dL (140 g/L; normal range, 12.0-15.0 g/dL) and a platelet count of 290 × 103/µL (290 × 109/L; normal range, 100-450 × 103/µL). The urine analysis demonstrates no evidence of hematuria or proteinuria. A follow-up ultrasound is performed (see Figures 1 and 2), followed by magnetic resonance imaging (MRI) (see Figure 3).
ANSWER:
The ultrasound demonstrated complete placenta previa (see Figure 1). Additionally, at the site of previous cesarean section, there was significant thinning of the uterus with loss of the placental-uterine interface (see Figure 2). It was also difficult to visualize a plane between the bladder and the uterus and, because of this, placenta accreta or percreta was suspected. Additional Doppler imaging did not demonstrate serosal extension of the placental vascularity. The subsequent MRI scan (see Figure 3) also demonstrated focal loss of the uterine-placental interface (best visualized on the T2-weighted sequences) within the lower uterine segment at the site of previous cesarean section (Figure 4), which is consistent with at least placenta accreta. No placental invasion was visualized, but the fat plane between the bladder and the uterus was not clearly identified to rule out bladder invasion.
Placenta accreta was at one time a quite rare condition, but it is becoming increasingly more common. The etiology is thought to be the rising cesarean delivery rate, which reached an all-time high of 29.1% in the United States in 2004.[1] Other risk factors for placenta accreta include multiparity, increasing maternal age, endometrial defects, scarring of the uterus (Asherman syndrome), and most significantly, placenta previa. Placenta previa is implantation of the placenta in the immediate vicinity of the cervical canal. In complete placenta previa, the placenta covers the entire opening of the internal cervical os. In partial placenta previa, the placenta partially covers the internal cervical os. Marginal placenta previa and low lying placenta are also described; these occur when the placenta extends to the edge of the internal cervical os or within 2.0 cm of the internal cervical os, respectively. An important point is that most cases of complete previa early in the second trimester will resolve during the pregnancy.[1]
Placenta accreta is one of 3 different types of abnormal placentation. Placenta accreta, accounting for 75% of all the cases, is the most common presenting type. Placenta accreta occurs when the placental villi adheres directly to the myometrium but does not penetrate the muscular layer, with the complete or partial absence of the decidua basalis. Placenta increta accounts for 15% of all cases and is characterized by the adherence of placental villi directly to the myometrium and demonstrates penetration within the myometrium. Placenta percreta, the least common of the 3, is the penetration of the placental villi into the serosal layer of the uterus. There may also be direct attachment to adjacent organs. Although all 3 types are characteristically different, the literature many times collectively refers to abnormal placentation together as placenta accreta. The clinical history in this particular case is extremely important since a patient with a placenta previa and a history of 2 previous cesarean sections carries a risk of approximately 40% for placenta accreta. Imaging can help raise or lower the concern for accreta in high-risk patients, but it is not usually definitive, which limits its ability to change management in these patients.
Transabdominal and transvaginal ultrasonography remain the imaging modalities of choice in detecting placenta accreta. In women with a previous history of cesarean section, second trimester sonographic evaluation may be helpful. The location of the previous cesarean section should be closely examined because the placenta has a tendency to adhere to this area. MRI is commonly used when ultrasonography remains uncertain (please see below). Although the use of ultrasonography and MRI provide a high degree of suspicion of placenta accreta, there is no imaging study that can diagnose placenta accreta with absolute accuracy. This has been demonstrated in a number of recent studies that compared the imaging findings of placenta accreta to the pathologic evaluation. Sonographic findings that give a high index of suspicion of placenta accreta include, but are not limited to, loss of the hypoechoic retroplacental myometrial zone, thinned hyperechoic uterine-bladder interface, presence of placental lacunae, and focal exophytic masses within the bladder. Color Doppler imaging also aids in the evaluation of placenta accreta. The use of color-Doppler has improved the sensitivity of grayscale ultrasonography because it depicts the local vascular anatomy within the uterus and related organs.[2]
MRI has come to the forefront in the evaluation of placenta accreta. MRI findings that are suggestive of placenta accreta include uterine bulging, heterogeneous signal intensity within the placenta, and the presence of dark intraplacental bands on T2-weighted imaging.[3] There have been a limited number of studies that have compared the accuracy of MRI and ultrasonography in the diagnosis of placenta accreta. A recent study found that ultrasonography had a sensitivity of 77% and a specificity of 96%. In comparison, MRI had a sensitivity of 88% and a specificity of 100%. The superiority of MRI over ultrasonography, however, was not statistically significant.[1] In this study, all patients with ultrasonographic examinations suggestive of placenta accreta underwent MRI scanning. If the appearance of placenta accreta was suspected, the patient also underwent a dynamic gadolinium-enhanced MRI series. This confirmed the presence of deep invasion. Palacios et al studied 300 patients with suspected placenta accreta using gadolinium contrast in an attempt to classify the depth levels and topographic areas in relation to the posterior bladder wall.[4] The MRI scans where then compared to the pathologic findings. The results of this study, however, were not used to further define the screening characteristics of placenta accreta, but rather to establish a modified surgical technique. The aim was to reduce complications at the time of surgery. Because gadolinium crosses the placenta, and the half-life and safety profile in pregnancy has not been established, the American College of Radiology recommends its usage only if the benefits outweigh the potential risks. Kim et al defined the appearance of the placental myometrial interface using the half-Fourier acquisition single-shot turbo spin-echo (HASTE) sequence: it has 3 layers, including the inner low signal-intensity layer, middle high signal-intensity layer, and an outer low signal-intensity layer.[8] In placenta accreta, there was focal nonvisualization of the inner layer. The limitations of this study were that only 5 patients were included, all of whom had prior cesarean deliveries, and no comparative studies could be made. Since there is only a limited amount of literature describing the normal anatomy of this area with the use of fast sequences, MRI remains only an adjuvant to inconclusive ultrasonography findings, or it can be used to evaluate accreta when adherence occurs in the posterior or fundal portions of the uterus.[1,2,3]
Placenta accreta is potentially life-threatening to both mother and fetus. The immediate clinical consequence of placenta accreta is massive hemorrhage at the time of placental removal, and it is the most common indication for emergency intra- or postpartum hysterectomy.[1] Since it is known that placenta previa is a risk factor for placental accreta, it is common for a patient to present with third trimester painless vaginal bleeding. Complications such as hematuria may occur if placenta percreta is present, resulting from direct penetration into the bladder. Because of this, a urine analysis is sometimes performed. In a patient with imaging findings highly suggestive of placenta accreta, management must begin in the prenatal period. In this period, it is essential that a multidisciplinary approach be used to fully inform the patient and family of the potential outcomes and management options. The risks and benefits of extirpative versus conservative management should be adequately discussed with the patient. Extirpative management, with a scheduled cesarean section and hysterectomy at 35-37 weeks of gestation, may be performed. If the patient opts for uterine conservation to allow for subsequent pregnancy, there are measures that can be implemented. Commonly, cesarean section alone can be successful, since most cases of accreta are focal. Methotrexate administration and uterine artery embolization have been reported, and the literature has either demonstrated various results (with methotrexate) or has suggested no benefit (uterine artery embolization).[7] Whether extirpative or uterine-conserving management is chosen, it is important that the delivery be performed in a center with staff trained for complicated surgeries potentially involving the bowel or bladder, and appropriate equipment and resources should be available to handle the many significant complications that may be encountered at the time of the procedure. A blood bank capable of providing large volumes of blood in emergency situations is particularly important.[1,7]
Given the patient's findings on ultrasonography and MRI, a cesarean delivery was scheduled, with a high probability of hysterectomy. At the time of the cesarean delivery, the patient was 36 weeks and 5 days intrauterine gestation by ultrasonographic dating. As a result of the close approximation of the ureters and the increased risk of trauma during this procedure, the patient underwent bilateral ureteral stent placement for direct visualization of the ureters. After delivery of the fetus, a portion of the placenta remained tightly adherent to the uterus. The decision was made to proceed with a cesarean supracervical hysterectomy. The patient tolerated the procedure well. No complications were noted, and the patient was taken to the recovery room in stable condition. The pathologic findings were an area of thinning consistent with previous low-transverse incision, with scar formation on the anterior surface of the uterus. This scarred area was focally and markedly thinned to 2 mm in thickness. The placenta was adherent to this area. Examination of the surgical specimen displayed a uterus with focal changes of placenta accreta. The patient was discharged to home from the hospital 4 days after her surgery.
Figure 1
Figure 2
Figure 3
Figure 4
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