spectrum of abnormal placental villous adherence

The spectrum of abnormal placental villous adherence describes the degree to which there is an invasion of chorionic villi into the myometrium because of a defect in the decidua basalis.

Epidemiology

• placenta accreta:
  • the commonest type of placental invasion (~75% of cases)
  • occurs in ~1 in 7,000 pregnancies
  • combination of previous C-section and an anterior placenta previa raises the probability of a placenta accreta
  • maternal mortality of up to 7% depending on location
• placenta increta:
  • ~25% of cases
  • occurs in ~1 in 50,000 pregnancies
• placenta percreta:
  • ~5% of cases

The incidence of all forms of abnormal placental villous adherence is increasing, which is felt to be due to the increased practice of cesarean sections

Risk factors 

• prior cesarean section
• placenta previa
• advanced maternal age
• uterine anomalies
• intrauterine adhesion bands
• previous surgery

Pathology

Placental villous adherence is classified on the basis of the depth of myometrial invasion:

• placenta accreta:
  • mildest form 
  • villi are attached to the myometrium but do not invade the muscle
• placenta increta:
  • intermediate form
  • villi partially invade the myometrium
• placenta percreta:
  • severest form
  • villi penetrate through the entire myometrium or beyond serosa 

Radiographic features

Definite imaging features can vary depending on the extent of invasion.

Ultrasound

• may show placenta previa
• may show placental lacunae
  • variably-sized vascular structures in the placenta creating a "moth-eaten" or "Swiss cheese" appearance.
  • can be seen as parallel linear vascular channels extending from placental parenchyma into the myometrium: they tend to show turbulent flow (cf. placental venous lakes show laminar flow)
• abnormal color Doppler
  • turbulent flow, i.e. disruption of the normal continuous color flow in the myometrium
  • increased vascularity is seen in the myometrium, and even in the urinary bladder in cases of placenta percreta
• loss of retroplacental clear space
• reduced myometrial thickness: anterior myometrial thickness <1 mm

MRI

MR images may show:

• placenta previa
• uterine bulging
• heterogeneous signal intensity within the placenta
• dark intraplacental bands on T2 weighted images
• focal interruptions of myometrial wall
• tenting of the urinary bladder
• direct visualization of the invasion of pelvic structures by placental tissue

Siehe auch:

• variation in placental morphology
• Placenta membranacea
• Placenta accreta
• Placenta extrachorialis
• uterine anomalies
• Placenta praevia
• kleine Plazenta
• Placenta percreta
• low lying placenta
• Placenta increta
• Asherman-Syndrom
• placental venous lakes

und weiter:

• Placenta circumvallata