Prenatal identification of invasive placentation using magnetic resonance imaging (MRI): a systematic review and meta analysis

Objective: The diagnostic performance of MRI in detecting invasive placentation is unclear. The aim of this review was to systematically assess the performance of prenatal MRI in diagnosing the presence, the degree and the topography of disorders of invasive placentation and to explore the role of the different MRI signs in predicting these disorders. The diagnostic accuracy of ultrasound and MRI in the detection of invasive placentation was also compared. Methods: MEDLINE, EMBASE, CINAHL and The Cochrane Library including The Cochrane Database of Systematic Reviews, Database of Abstracts of Reviews of Effects and The Cochrane Central Register of Controlled Trials were searched electronically utilizing combinations of the relevant medical subject heading terms, key words and word variants for “Placenta accreta” and “Magnetic resonance imaging”. Only studies reporting a prospective diagnosis of invasive placentation at the time of the MRI scan or where the radiologist were blinded to the final results were included in the analysis. The MRI signs explored were: 1) uterine bulging, 2) heterogeneous signal intensity, 3) dark intra-placental bands on T2 weighed sequences, 4) focal interruption of myometrium, 5) tenting of the bladder). Two reviewers (FD, CI) independently extracted data.. Quality of studies was assessed using the revised tool for the quality assessment of diagnostic accuracy studies (QUADAS-2). Summary estimates of sensitivity, specificity, positive and negative likelihood ratios and diagnostic odds ratio (DOR) were based, depending on the number of studies, upon DerSimonian-Laird random-effect or hierarchical summary receiver operating characteristic (HSROC) model. Results: A total of 18 studies including 1010 pregnancies at risk for invasive placentation were included. The overall diagnostic accuracy of MRI in detecting the presence of invasive placentation was: sensitivity: 94.4% (95% CI 86.0-97.9), specificity: 84.0% (95% CI 76.0-89.8), +LR: 5.91 (95% CI 3.73-9.39), -LR: 0.07 (95% CI 0.02-0.18), DOR: 89.0 (95% CI 22.8-348.1). MRI had a high predicting accuracy in assessing both the depth and the topography of placental invasion. All the five MRI signs showed a good predictive accuracy in the diagnosis of disorders of invasive placentation. There was no difference either in the sensitivity (p=0.24) and in the specificity (p=0.91) between US and MRI for the detection of invasive placentation. Conclusions: Prenatal MRI is highly accurate in diagnosing disorders of invasive placentation. MRI should be scheduled if parametrial invasion is suspected and a hysterectomy is planned. Large population based studies are needed in order to assess whether US can reliably predict the depth and the topography of placental invasion compared to MRI.