The presence of placental lacunae in the second trimester scan has been shown to have the highest sensitivity and positive predictive value for placenta accreta [37]. Comstock et al [37] observed lacunae in a majority of placenta accreta patients in second trimester scans. When lacunae are multiple, large, and irregular, they are highly suggestive of placenta accreta, but placenta accreta can occur in their absence. On grayscale transabdominal US, the imaging findings that suggest placenta accreta include the presence of intraplacental lacunae (sonolucent spaces that can have slow-moving to more suspicious turbulent moving flow, Placenta Accreta Spectrum Disorder also called intraplacental lakes), loss of the normal hypoechoic retroplacental zone or clear space, reduced myometrial thickness of <1 cm, placental bulging (ballooning of the uterus containing placenta from its expected plane into surrounding tissue, usually into the urinary bladder), and the presence of bladder wall abnormalities. Interruption, thickening, or irregularity of the uterine serosa-bladder line interface has been reported to have high sensitivity and specificity for accreta, more striking as the depth of invasion progresses [2]. Sensitivity of US has been reported to range from 77% to 93%, with positive predictive value of 65% to 93%, and prevalence of 9% to 44% [6,16,37,38,46]. As an isolated finding, loss of the normal retroplacental zone has a reported sensitivity of only 52% and specificity of 57%, with a high false-positive rate of 21% because the normal retroplacental zone may also be absent in normal anterior placentas as well [2,46-48]. Another limitation in the assessment for placental invasion is when the placenta is not low lying. Recognition of a history of prior surgery in these cases may be helpful, as well as meticulous attention to placental morphology and structure.
Placenta Accreta Spectrum Disorder. The presence of placental lacunae in the second trimester scan has been shown to have the highest sensitivity and positive predictive value for placenta accreta [37]. Comstock et al [37] observed lacunae in a majority of placenta accreta patients in second trimester scans. When lacunae are multiple, large, and irregular, they are highly suggestive of placenta accreta, but placenta accreta can occur in their absence. On grayscale transabdominal US, the imaging findings that suggest placenta accreta include the presence of intraplacental lacunae (sonolucent spaces that can have slow-moving to more suspicious turbulent moving flow, Placenta Accreta Spectrum Disorder also called intraplacental lakes), loss of the normal hypoechoic retroplacental zone or clear space, reduced myometrial thickness of <1 cm, placental bulging (ballooning of the uterus containing placenta from its expected plane into surrounding tissue, usually into the urinary bladder), and the presence of bladder wall abnormalities. Interruption, thickening, or irregularity of the uterine serosa-bladder line interface has been reported to have high sensitivity and specificity for accreta, more striking as the depth of invasion progresses [2]. Sensitivity of US has been reported to range from 77% to 93%, with positive predictive value of 65% to 93%, and prevalence of 9% to 44% [6,16,37,38,46]. As an isolated finding, loss of the normal retroplacental zone has a reported sensitivity of only 52% and specificity of 57%, with a high false-positive rate of 21% because the normal retroplacental zone may also be absent in normal anterior placentas as well [2,46-48]. Another limitation in the assessment for placental invasion is when the placenta is not low lying. Recognition of a history of prior surgery in these cases may be helpful, as well as meticulous attention to placental morphology and structure.