Patient selection: pregnant woman with placenta previa, usually in the third trimester
Exam: pelvic MRI
Parameters:
(1) intraplacental T2-weighted dark band (nodular or linear areas of low signal intensity on T2-weighted images)
(2) intraplacental abnormal vascularity (tortuous vessels with enlarged flow voids deep within the placenta)
(3) placental bulge (outward projection of the uterine contour, sometimes with extension into neighboring organ such as the bladder)
(4) heterogeneous placenta on T2-weighted images (unrelated to dark bands and abnormal vascularity, above)
(5) myometrial thinning (focal thing of the myometrium AND loss of the dark uteroplacental interface on T2-weighted images)
(6) placental protrusion sign at the internal cervical os (protrusion of the placenta into the external os)
|
Status of Each Finding
|
Points
|
|
definitely negative
|
1
|
|
probably negative
|
2
|
|
neutral/indeterminate
|
3
|
|
probably positive
|
4
|
|
definitely positive
|
5
|
total score =
= SUM(points for all 6 parameters)
Interpretation:
• minimum score: 6
• maximum score: 30
• The higher the score the greater the likelihood of an invasive/adherent placenta.
• An experienced radiologist tended to perform better than a less experienced one.
• Placenta percreta tends to have a higher score than placenta increta, which in turn is greater than placenta accreta.
Performance:
• The area under the ROC curve is 0.92.
