Douglas L. Brown MD, Presenter: Nothing to Disclose

Sara Mannarelli Durfee MD, Abstract Co-Author: Nothing to Disclose

Clare Mary C. Tempany MD, Abstract Co-Author: Nothing to Disclose

To describe the MR features and pitfalls in diagnosing retained placenta accreta (used here in the general sense to indicate any degree of myometrial involvement) in the postpartum or postabortion period.

A computerized database search revealed 8 patients where placenta accreta was suspected in postpartum or postabortion patients by ultrasound and who then underwent pelvic MR. The MR signal characteristics and post-gadolinium findings were recorded.Final diagnosis was determined by surgical pathology (n=5) or clinical outcome (n=3).

MR was correct in diagnosing or excluding accreta in 6 of 8 (75%) cases, though one of these was only partially correct. In 2 cases, MR was interpreted as no accreta, one of which was correct. In the false negative case, the myometrium was interpreted as thinned but intact by MR, however pathology showed placenta accreta. In 6 cases, accreta was suspected on MR and 5 of these were correct. One of these 5 cases was only partially correct however, as myometrial involvement was felt to extend to the uterine serosa by MR, but by pathology there was only microscopic placenta accreta. In the false positive case, pathology revealed retained placenta in the uterine cavity but no myometrial involvement. In these 2 latter cases, it appeared that hypervascular myometrium adjacent to retained placenta simulated myometrial invasion. In all 6 cases with placenta accreta, the retained placental tissue was heterogeneously hyperintense to myometrium on T2-weighted sequences and essentially isointense to myometrium on T1-weighted sequences. Gadolinium was used in 5 of the 6 cases with accreta and in all 5, the retained placental tissue enhanced, though to variable degrees.

While placenta accreta can usually be diagnosed correctly by MR in the postpartum and postabortion period, potential pitfalls include distinguishing thinned versus invaded myometrium and distinguishing myometrial invasion versus focal hypervascularity of the myometrium adjacent to retained placenta.

Brown, D, Durfee, S, Tempany, C, MRI of Retained Placenta Accreta in Postpartum and Postabortion Patients.  Radiological Society of North America 2004 Scientific Assembly and Annual Meeting, November 28 - December 3, 2004 ,Chicago IL. http://archive.rsna.org/2004/4414622.html