Chemical Shift Artifact on Steady-State MRI Sequences for Detection of Vesical Wall Invasion in Placenta Percreta.

Abstract

Antenatal diagnosis of the invasiveness of a placenta percreta helps in planning the surgical approach, reducing blood loss and morbidity. Doppler sonography is the mainstay diagnostic modality with a sensitivity of 80-95%. With the advent of high magnetic field MRI techniques, there has been recent interest in evaluation of placenta by MRI. On an extensive PUBMED search, we could not find any citations describing imaging, ultrasound, or MRI features to evaluate vesical wall invasion by placenta percreta. We attempt to evaluate transmyometrial vesical wall invasion by placenta percreta using chemical shift artifact as a marker of intact bladder-myometrial interface on steady-state MRI sequences. This is a prospective observational study, conducted at a university hospital. We have compiled clinico-radiological criteria for diagnosis of invasive placentae based on the existing body of evidences, in four patients. We further go on to analyze a specific proposed sign on a newly introduced MR imaging sequence i.e., loss of chemical shift artifact (India ink line) on steady-state GRE sequence (TrueFISP), to diagnose transmyometrial vesical invasion in placenta percreta. Though the sample size is small, the sensitivity, specificity, positive, and negative predictive value of the proposed sign for the purpose was 100 %. Loss of chemical shift artifact (India ink line) on steady-state GRE sequences at the vesico-myometrial junction in case of invasive placentae confirms vesical wall invasion, a prospective diagnoses of which can help in planning the surgical protocol and preventing potentially fatal blood loss.