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Placenta Accreta

Sonogram demonstrating absence (arrows) of the intervening myometrium between the placenta and uterine serosa
Color Doppler image demonstrating absence of intervening myometrium (short arrow) and abnormal bladder-uterine wall vascularization (long arrow)

Sonogram demonstrating numerous vascular lacunae (asterisks) within the placenta in a patient with placenta accreta

Findings:

The normally hypoechoic retroplacental zone is absent (arrows).

 

Discussion:

Placenta accreta is the general term that applies to a subset of abnormalities in placental development including; placenta accreta, increta and percreta. This abnormality results from an abnormal adherence of the placenta to the uterus with subsequent failure of the placenta to separate after delivery of the fetus. The etiology is felt to result from a deficiency in the decidua basalis in which the decidua is partially or completely replaced by loose connective tissue. In normal pregnancy, chorionic villi attach to the decidua and cytotrophoblasts invade as far as the first third of the myometrium . In placenta accreta, chorionic villi and/ or cytotrophoblasts directly attach to the myometrium with little or no intervening decidua . The depth at which chorionic villi and cytotrophoblasts are found determines the exact classification of the variant forms. In placenta increta, trophoblasts invade the myometrium; in placenta percreta, chorionic villi extend through the entire uterine wall and serosa, sometimes penetrating adjacent tissue, most commonly the bladder.

Drawing illustrating placenta accreta, increta and percreta

Modified from: Kim H, Hill MC, Winick AB, Shen T. Prenatal diagnosis of placenta accreta with pathologic correlation. Radiographics 18:237-242, 1998


The prevalence of placenta accreta is estimated to be 1 in 2500 pregnancies. Placenta previa, or implantation over the cervical os, carries a risk factor for placenta accreta of approximately 5-10%, which rises to 24% with one prior Cesarean section and to 67% with four or more. The association with a previous uterine scar suggests that decidual development, which is impaired over scar tissue, is a critical component for normal placentation. Although several cases of placenta accreta, detected in the first trimester with ultrasound, have been reported in the past year, it usually remains undetected until a catastrophic hemorrhage develops during the third stage of labor.


Sonographic Findings


An analysis of the retroplacental area is important in making the diagnosis of placenta accreta. In placenta accreta, the normally hypoechogenic, 1- to 2-cm area is absent or markedly thinned (< 2 mm), and there is loss of the normal decidual interface between the placenta and myometrium. In addition, thinning or disruption of the hyperechogenic uterine serosa-bladder interface may be seen, as well as the presence of focal exophytic masses. Often, there are prominent hypoechogenic–anechoic spaces (lacunae) in the placenta and marked periplacental vascularity on color Doppler sonography. The presence of lacunae, within the placental parenchyma, particularly when numerous and concentrated in the lower uterine segment, appears to be a separate risk factor for placenta accreta, first reported by Guy et al. These authors noted visible pulsatile flow in them and suggested that this implied transmission of high pulse pressure from the deep arterial system. The color Doppler criteria suggestive of placenta accreta have been described by Chou et al. They include: 1) A diffuse lacunar flow pattern exhibiting diffusely dilated vascular channels scattered throughout the whole placenta and the surrounding myometrial or cervical tissues. High-velocity pulsatile venous-type flow was found in the sonolucent vascular spaces. 2) A focal lacunar flow pattern showing irregular sonolucent vascular lakes with turbulent lacunar flow distributed regionally or focally within the intraparenchymal placental area. 3) Interphase hypervascularity with abnormal blood vessels linking the placenta to the bladder with high diastolic arterial blood flow. 4) Markedly dilated peripheral subplacental vascular channels with pulsatile venous-type flow over the uterine cervix. 5) Absence of subplacental vascular signals in the areas lacking the peripheral subplacental hypoechoic zone. When placenta accreta occurs on the posterior or lateral walls of the uterus, it may be difficult to detect by ultrasound. Levine and colleagues suggested that, in those patients with posteriorly implanted placenta at risk for accreta, magnetic resonance imaging should be used when ultrasound could not rule out the presence of accreta.


Treatment


Although the definitive treatment for placenta accreta is a hysterectomy, conservative management of placenta accreta is possible. Conservative management, particularly for those patients who wish to preserve fertility includes: curettage, oversewing of the placental bed, and ligation of the uterine arteries or the anterior divisions of the internal iliac arteries.

References:

Chen YJ, Wang PH, Liu WM et al Placenta accreta diagnosed at 9 weeks’ gestation. Ultrasound Obstet Gynecol 19:620-22, 2002


Chou MM, Ho ESC, Lee YH Prenatal diagnosis of placenta previa accreta by transabdominal color Doppler ultrasound Ultrasound Obstet Gynecol 15: 28-35, 2000


Catanzarite VA, Stanco LM, Axhrimmer DR, Conroy C Managing placenta previa / accreta. Contemporary OB/Gyn, May, 1996


Committee Opinion #266: Placenta accreta. ACOG Committee on Obstetric Practice. Obstet Gynecol 99:169-170, 2002


Finberg H, Williams J. Placenta accreta: prospective sonographic diagnosis in patients with placenta previa and prior cesarean section. J Ultrasound Med 11: 333–43, 1992


Kim H, Hill MC, Winick AB, Shen T. Prenatal diagnosis of placenta accreta with pathologic correlation. Radiographics 18:237-242, 1998


Clarke SL, Koonings PP, Phelan JP. Placenta previa/accreta and prior cesarean section. Obstet Gynecol 66: 89–92, 1985


Harris RD, Alexander RD. Ultrasound of the placenta and umbilical cord. In Callen PW, ed. Ultrasonography in Obstetrics and Gynecology, 4th edn. Philadelphia: W.B. Saunders, 2000: 597–614


Pasto ME, Kurtz AB, Rifkin MD, Cole-Beuglet C, Wapner R, Goldberg B. Ultrasonographic finding in placenta increta. J Ultrasound Med 2: 155–9, 1983


Tabsh KMA, Brinkman CR, King W. Ultrasound diagnosis of placenta increta. J Clin Ultrasound 10: 288–90, 1982


Cox SM, Carpenter RJ, Cotton DB. Placenta percreta: Ultrasound diagnosis and conservative surgical management. Obstet Gynecol 71: 454–6, 1988


Guy G, Peisner DB, Timor-Tritsch IE. Ultrasonographic evaluation of uteroplacental blood flow patterns of abnormally located and adherent placentas. Am J Obstet Gynecol 163: 723–7, 1990


De Mendonca L. Sonographic diagnosis of placenta accreta. J Ultrasound Med 7: 211–5, 1988


Finberg H, Williams J. Placenta accreta: prospective sonographic diagnosis in patients with placenta previa and prior cesarean section. J Ultrasound Med 11: 333–43, 1992


Lerner J, Deane S, Timor-Tritsch IE. Characterization of placenta accreta using transvaginal sonography and color Doppler imaging. Ultrasound Obstet Gynecol 5: 198–201, 1995


Chou M, Ho E, Lu F, Lee Y. Prenatal diagnosis of placenta previa/ accreta with color Doppler ultrasound. Ultrasound Obstet Gynecol 2: 293–6, 1992


Jauniaux E, Toplis P, Nicolaides K. Sonographic diagnosis of a non-previa placenta accreta. Ultrasound Obstet Gynecol 7: 58–60, 1996


Levine D, Hulka CA, Ludmir J, Li W, Edelman RR. Placenta accreta: evaluation with color Doppler ultrasound, power Doppler ultrasound, and MR imaging. Radiology 205: 773–6, 1997


Wheeler TC, Anderson TL, Kelly J, Boehm FH. Placenta previa increta diagnosed at 18 weeks’ gestation. J Reprod Med 41: 198–200, 1996


Cox S, Carpenter R, Cotton D. Placenta percreta: Ultrasound diagnosis and conservative surgical management. Obstet Gynecol 71: 454, 1988


Jauniaux E, Toplis PJ, Nicolaides KH. Sonographic diagnosis of a non-previa placenta accreta. Ultrasound Obstet Gynecol 7: 58, 1996


Guy G, Peisner S, Timor-Tritsch I. Ultrasonographic evaluation of uteroplacental blood flow patterns of abnormally located and adherent placentas. Am J Obstet Gynecol 163: 723, 1990


Komulainen MH, Vayrynen MA, Kauko ML, Saarikoski S. Two cases of placenta accreta managed conservatively. Eur J Obstet Gynecol Reprod Biol 62: 135, 1995


Gibb DM, Soothill PW, Ward KJ. Conservative management of placenta accreta. Br J Obstet Gynaecol 101: 79–80, 1994


Hollander DI, Pupkin MJ, Crenshaw MC, Nagey DA. Conservative management of placenta accreta. J Reprod Med 33: 74–8, 1988


Miller DA, Chollet JA, Goodwin TM. Clinical risk factors for placenta previa-placenta accreta. Am J Obstet Gynecol 177: 210–4, 1997


Spirt BA, Gordon CP. Sonography of the placenta. In Fleischer AC, Manning FA, Jeanty P, Romero R, eds. Sonography in Obstetrics and Gynecology Principles and Practice, 5th edn. Stamford: Appleton & Lange, 1996: 173


Samberg I, Oettinger M, Grishkan A, Sharf M. Cervical placenta percreta. Clin Exp Obstet Gynecol 8: 156–9, 1981


Wang PH, Chao HT, Yuan CC, Cinn JJ, Yen MS. Placenta previa accreta with cervical involvement causing tenacious postpartum hemorrhage. Chin Med J (Taipei) 61: 116–9, 1998

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Peter W. Callen, M.D.
Professor of Radiology, Obstetrics, Gynecology and Reproductive Science
University of California Medical Center, San Francisco, California