The morbidly adherent placenta: when and what association of signs can improve MRI diagnosis? Our experience

Abstract

Purpose: We aimed to verify whether combination of specific signs improves magnetic resonance imaging (MRI) accuracy in morbidly adherent placenta (MAP).

Methods: MRI findings for MAP were retrospectively evaluated in 27 women. Histopathology was the reference standard, showing MAP in eight of 27 cases. Specificity, sensitivity, positive predictive value, and negative predictive value were calculated for all MRI signs. Two skilled radiologists analyzed MRI findings, resolving discrepancies by consensus, using three alternative diagnostic criteria during three consecutive sections. First criterion: at least one of reported MRI signs indicates MAP and the absence of any sign is normal; second criterion: at least one statistically significant sign indicates MAP and no sign or nonsignificant sign is normal; third criterion: at least two statistically significant signs indicate MAP and no sign, nonsignificant sign, or only one significant sign is normal.

Results: Using the first criterion yielded an unacceptable rate of false positive results (78.9%). Using the second criterion there were less false positive results (31.5%), and diagnostic accuracy of the second criterion was significantly higher than the first; the third criterion correctly classified 100% of cases.

Conclusion: Only specific MRI signs can correctly predict MAP at histopathology, particularly when multiple (at least two) specific signs are observed together.

Figure 1. a, b

MRI showing normal placenta in a 39-year-old woman at 36 weeks of gestational age. Sagittal (a) and axial (b) T2-weighted images show normal “pear shaped” uterus, with the placenta (P) extending to the edge of internal os (arrow) without covering it. The placenta is homogeneous with thin hypointense regular lines that represent septa. The three distinct layers of myometrium are visible, with the inner and outer layers showing as hypointense and the inner one showing as intermediate intensity (arrowhead).

Figure 2. a–c

MRI in a 39-year-old woman at 32 weeks and 5 days of gestational age. Sagittal (a) and axial (b) T2-weighted MRI image taken perpendicularly to the long uterine axis show thinned myometrial border (myometrial thinning sign) with loss of the trilaminate structure of the myometrium (a, thin black arrow), which is focally interrupted (focal interruption sign) (a and b, white arrowhead). The normal trilaminate structure of the myometrium is seen cranially (a, white arrow). The upper contour of the bladder is also stretched and pinched (tenting of the bladder sign) (a, black arrowhead). The posterior contour of the uterus is bulged (uterine bulging sign) (a, white line). Axial T2-weighted image (c), taken distally near the bladder, shows inhomogeneous signal intensity of the placenta with a vascular lacuna (heterogeneous signal sign) (c, white curved arrow) and intraplacental dark thick band (dark band sign) with longest diameter >2 cm (c, white arrows). The cesarean section was performed a week later and histopathology confirmed morbidly adherent placenta (MAP, placenta increta) at the anterior lower third of the uterus. P, placenta.

Figure 3

MRI in a 41-year-old woman at 28 weeks and 5 days of gestational age. The coronal oblique T2-weighted image shows tortuous and enlarged intraplacental flow voids (abnormal vascularity sign) well evident at the left anteroinferior side of the uterus (arrow); the placenta seems to directly invade the vesicouterine space (direct visualization of the nearest tissue invasion sign, arrowhead). Cesarean section was performed five days after MRI and histopathology after hysterectomy confirmed MAP (placenta percreta). P, placenta.

Figure 4

Bar chart showing distribution of MRI signs in the whole study population (i.e., cases with MAP diagnosis at histopathology and cases negative for MAP at histopathology and cesarean section). MT, myometrial thinning; FI, focal interruption of myometrial border; HS, heterogeneous signal; DB, T2-weighted dark intraplacental bands; AV, intraplacental abnormal vascularity; UB, uterine bulging; DI, direct visualization of nearest tissue invasion; TB, tenting of the bladder.

Figure 5

Bar chart showing distribution of MRI signs in the eight patients diagnosed with MAP at histopathology. MT, myometrial thinning; FI, focal interruption of myometrial border; HS, heterogeneous signal; DB, T2-weighted dark intraplacental bands; AV, intraplacental abnormal vascularity; UB, uterine bulging; DI, direct visualization of nearest tissue invasion; TB, tenting of the bladder.