PLACENTA ACCRETA

PLACENTA INCRETA

PLACENTA PERCRETA

 

Incidence of placenta accreta vary widely, ranging from 1 in 540 to 1 in 93,000 deliveries (1-5).

It is thought to result from either a primary deficiency of or secondary loss of decidual elements (decidua basalis).

 

CLASSIFICATION

 

Type

Degree of invasion of chorionic villi

Pathology

Accreta

Attach superficially to myometrium (80%)

Occurs when the decidua basalis is partially or totally absent in conjunction with an imperfect development of the Nitabuch membrane, a fibrinoid layer that separates the decidua basalis from the placental villi.

Increta

Deep into myometrium (15%)

Results when placental villi invade the myometrium.

Percreta

Through the myometrium and into serosa (5%)

Represents the greatest degree of severity. Defined as the penetration of the trophoblast through the myometrium and into or through the peritoneum, it sometimes extends to adjacent structures such as the bladder

 

RISK FACTORS

 

Risk factors for the development of placenta accreta / increta / percreta

Placenta previa

Previous cesarean section

Previous myomectomy or reconstructive uterine surgery

Asherman's syndrome

Multiparity

Advanced maternal age

Submucous leiomyomata

 

The major risk factor for abnormal placental implantation is the combination of an anterior placenta previa with a uterine scar that usually resulted from a previous cesarean section. Placenta previa itself raises the risk for accreta due to implantation over a highly vascular, poorly contractile lower uterine segment; an existing scar in this same area obviously compounds the risk.

Clark and colleagues demonstrated the effect of previous cesarean section on the incidence of placenta accreta. They showed that the risk of placenta previa increases proportionately with the number of previous cesarean sections (0.26% in an unscarred uterus, and up to 10% in women with four or more previous cesarean section) (6). The researchers further showed that the association of placenta previa and a previous cesarean section greatly increases the chances of developing placenta accreta. Patients with no prior uterine scarring had only a 5% incidence of accreta, compared with "veterans" of four previous cesarean sections, who had an incidence of up to 67%.

 


Risk of placenta accreta relative to uterine scarring and presence of placenta previa

Number of prior cesarean
sections

Incidence of
placenta previa (%)

Incidence of accreta when
previa is also present (%)

0

0.26

5

1

0.65

24

2

1.8

47

3

3.0

40

4

10.0

67

The risk of placenta previa increases proportionately with the number of prior cesarean deliveries.

Reference : Clark SL, Koonings PP, Phelan JP. Placenta previa / accreta and prior cesarean section. Obstet Gynecol. 1985;66:89-92.

 

 

ULTRASOUND

 

Link to Ultrasound of Placenta accreta

 

 

 

 

 

Video clip of Placenta Increta

 

 

 

 

MAGNETIC RESONANCE IMAGING IN PLACENTA ACCRETA

Magnetic resonance imaging is also useful as an adjunct in the diagnosis of placenta accreta (11)

1.      T-2 and Short Tau Inversion Recovery images are particularly useful since they can demonstrate the presence of placental tissue with high signal intensity, making it easier to distinguish the placenta from the myometrium (12).

2.      Levine and colleagues studied 19 patients at risk for developing placenta accreta with both Ultrasound and MRI. (13).

·         Five cases of lower-uterine segment placenta accreta were diagnosed with a high level of confidence using vaginal and power Doppler U/S. In one patient with a posterior placenta who had previously undergone myomectomy, MRI provided the diagnosis of placenta accreta, which was not well depicted by U/S.

·         The researchers concluded that, in these patients, MRI was particularly helpful in cases of posterior placenta where ultrasonographic evaluation is not diagnostic.

3.      Other investigators have used MRI to assess bladder invasion in cases of placenta percreta (12,14). As with power amplitude ultrasonic angiography, prospective studies comparing MRI with gray-scale sonography and conventional color Doppler for the diagnosis of placenta accreta are still lacking. This technique appears safe for the fetus, however, and is a promising advance in prenatal diagnosis.

4.      According to the most recent Committee Opinion of the American College of Obstetricians and Gynecologists, MRI is not recommended in the first trimester, but neither has it been associated with any known adverse fetal effects (15). As with the other imaging techniques MRI is currently used to complement, rather than replace, information obtained via standard sonographic imaging.

 

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 three layers - inner low signal intensity layer, middle high signal intensity layer and an outer low signal intensity layer.

In accreta there was focal non-visualization of the inner layer (16). However, this was a retrospective study in which the reviewer knew the diagnosis and all five patients had had a Cesarean section. There are no comparative MRI examinations of the myometrium and placental interfaces and bladder interfaces in patients with placenta previa and previous Cesarean sections and no accreta. When using the criteria of attenuation or non-visualization of the uterine wall in the area of the placenta, interruption of the tissue plane between the myometrium and bladder wall by masses or overt invasion of the myometrium by the placenta, there were five false negatives. Since only pathology-proven cases were considered, there is no estimation of how many false positives there could have been at that institution (17). Two of the false negatives had placenta percreta and one placenta increta.

Ito et al. found no additional information by MRI in a case of increta, but had used a transurethral ultrasound probe to evaluate the myometrium beforehand, and so had gained as much information as possible from ultrasound (18).

 

 

PREDISPOSING CONDITIONS
  • Previous placenta previa (10%).
  • Previous cesarean section.
    When both the above factors occur together, the risk of placenta accreta is 25%.
    When there is a prior history of four prior cesarean sections and placenta previa the incidence increases to 67% (4).
  • Increasing parity.
  • Previous D & C.
  • Endometritis.
  • Adenomyosis.
  • Asherman's Syndrome (5).

 

COMPLICATIONS

 

Complications include postpartum hemorrhage and its resultant coagulopathy, preterm delivery, postpartum curettage and infection, cesarean hysterectomy, and death

 

 

 

REFERENCES
  1. Finberg HJ, Williams JW. Placenta accreta: Prospective monographic diagnosis in patients with placenta previa and prior cesarean section. J Ultrasound Med 1992;11:333.
  2. Hoffman-Tretin JC, Koenigsberg M, Rabin A et.al.  Placenta accreta: Additional sonographic observations. J Ultrasound Med 1992;11:29.
  3. Hull AD, Salerno CC, Saenz CC et.al. Three dimensional ultrasonography and diagnosis of placenta percreta with bladder involvement. J Ultrasound Med 1999;18:853-856.
  4. Clark Sl, Koonings PP, Phelan JP. Placenta previa / accreta and prior caesarean section. Obstet Gynecol 1985;66:89-92.
  5. Nelson LH. Ultrasonography of the placenta - A review. Laurel, MD, AIUM, 1994. 2
  6. Clark SL, Koonings PP, Phelan JP. Placenta previa/accreta and prior cesarean section. Obstet Gynecol. 1985;66:89-92.
  7. Breen JL, Neubecker R, Gregori CA, et al. Placenta accreta, increta, and percreta. A survey of 40 cases. Obstet Gynecol. 1977;49:43-47.
  8. Pasto ME, Kurtz AB, Rifkin MD, et al. Ultrasonographic findings in placenta increta. J Ultrasound Med. 1983;2:155-159.
  9. Hoffman-Tretin JC, Koenigsberg M, Rabin A, et al. Placenta accreta. Additional sonographic observations. J Ultrasound Med. 1992;11:29-34.
  10. Chou MM, Ho ES, Lee YH. Prenatal diagnosis of placenta previa accreta by transabdominal color Doppler ultrasound. Ultrasound Obstet Gynecol. 2000;15:28-35.
  11. Silver LE, Hobel CJ, Lagasse L, et al. Placenta previa with bladder involvement: new considerations and review of the literature. Ultrasound Obstet Gynecol. 1997;9:131-138.
  12. Thorp JM Jr, Councell RB, Sandridge DA, et al. Antepartum diagnosis of placenta previa percreta by magnetic resonance imaging. Obstet Gynecol. 1992;80:506-508.
  13. Levine D, Hulka CA, Ludmir J, et al. Placenta accreta: evaluation with color Doppler US, power Doppler US, and MR imaging. Radiology. 1997;205:773-776.
  14. Bakri YN, Rifai A, Legarth J. Placenta previa-percreta: magnetic resonance imaging findings and methotrexate therapy after hysterectomy. Am J Obstet Gynecol. 1993;169:213-214.
  15. American College of Obstetricians and Gynecologists, Committee on Obstetric Practice. Guidelines for Diagnostic Imaging During Pregnancy. ACOG Committee Opinion. No. 158, September 1995.
  16. Kim JA, Narra VR. Magnetic resonance imaging with true fast imaging with steady-state precession and half-Fourier acquisition single-shot turbo spin-echo sequences in cases of suspected placenta accreta. Acta Radiol 2004; 45: 692-698.
  17. Lam G, Kuller J, McMahon M. Use of magnetic resonance imaging and ultrasound in the antenatal diagnosis of placenta accreta. J Soc Gynecol Investig 2002; 9: 37-40. Links  
  18. Ito T, Katagiri C, Ikeno S, Takahashi H, Nagata N, Terakawa N. Placenta previa increta penetrating the entire thickness of the uterine myometrium: ultrasonographic and magnetic resonance imaging findings. J Obstet Gynaecol Res 1999; 25: 303-307