Does MRI Help or Hurt When Making a Diagnosis of Placenta Accreta?

BACKGROUND AND PURPOSE: 

• Incidence of Placenta Accreta Spectrum Disorder is rising  
  • Estimated at 1/500-1/300 pregnancies  
• Ultrasound is the standard radiologic modality, while MRI remains controversial  
• Einerson et al. (AJOG 2018) sought to determine if MRI contributes to the sonographic diagnosis of Placenta Accreta Spectrum Disorder

METHODS: 

• Retrospective cohort study  
• Participants 
  • Patients undergoing both ultrasound and MRI during 2nd and 3rd trimesters
  • Placenta Accreta Spectrum Disorder suspected (ultrasound or risk factors)  
• Ultrasound risk factors 
  • Numerous echolucent placental lacunae | Loss of a normal retroplacental hypoechoic space | Loss of detectable myometrium | Bladder wall irregularity | Presence of abnormal subplacental vascularity 
• Other clinical risk factors (if no suggestive US findings) included  
  • History of endometrial ablation or cavity-entering myomectomy | ≥3 cesarean deliveries in the setting of placenta previa | Suboptimal visualization of the placenta by US 
• MRI decision left to MFM/surgical and radiology providers  
• Diagnostic accuracy was verified by surgical and histopathologic diagnosis at the time of delivery 
• Primary outcome  
  • Change in diagnosis from sonographic interpretation that could alter clinical management 
• Secondary outcomes 
  • Correlation of radiologic diagnoses with surgical and histopathologic diagnosis

RESULTS: 

• 78 patients were included   
• Diagnosis that could alter clinical management occurred in 36% of cases 
• MRI correctly  
  • Changed diagnosis in 19%  
  • Confirmed diagnosis in 44% 
• MRI incorrectly  
  • Changed diagnosis in 17% 
  • Confirmed diagnosis in 21% 
• MRI was not more likely to change a diagnosis in the 24 cases of posterior and lateral placental location compared to anterior location (33% vs 37%, P = .84) 
• MRI resulted in overdiagnosis in 23% and in underdiagnosis in 14% of all cases 
• In 14 severe Placenta Accreta Spectrum Disorder (percreta) cases, MRI altered only 2 diagnoses, both downgraded  
  • One was a correct downgrade to Placenta Accreta Spectrum Disorder (accreta and increta) and the other was an incorrect downgrade  
• PPV for severe Placenta Accreta Spectrum Disorder 
  • MRI: PPV 61% (95% CI, 0.41–0.78) 
  • Ultrasound: PPV 73% (95% CI, 0.45–0.91) 
• Proportion of accurate diagnoses with MRI did not improve over time despite increasing volume and increasing numbers of changed diagnoses

CONCLUSION: 

• The addition of MRI to the assessment of Placenta Accreta Spectrum Disorder can often lead to an incorrect diagnosis  
• The authors advise that MRI should not be used routinely as an adjunct to ultrasound in the diagnosis of Placenta Accreta Spectrum Disorder

Learn More – Primary Sources: 

Magnetic resonance imaging is often misleading when used as an adjunct to ultrasound in the management of placenta accreta spectrum disorders