TIPPS: The International Placental Pathology Study Group?

Some years ago, I had initiated a group, MAPS,  (MidAmerica Placenta Study group) with the idea that it would encompass placental pathologists who could easily get together to meet. I sent out a newsletter with placental slides for discussion. We had 2 meetings. One locally in which the pathologists came more or less locally, from St. Louis, Detroit, Cleveland, Chicago, and Birmingham Alabama. Kurt Benirschke came from San Diego. The next meeting was in Toronto preceding the SPP meeting and by then we had members from all over as far away as Australia. Given the capability of the internet for rapid communication, I think we should form The International Placental Pathology Study Group, (TIPPS Group).

I am going to use a recent paper to provide an example/argument for the value of an online interactive placental/perinatal pathology group (1). The paper reviews the association of a blood clot received with the placenta with finding basal plate myofibers on microscopic examination.  The logic of the study is that if a placenta has focal adherence to the myometrium, it will not separate immediately after postpartum contraction of the uterus. However, a portion will separate, and beneath that separated area of retained placenta there will be decidual hemorrhage. Recent reports that basal plate myofibers are a marker of increased risk for placental accreta in subsequent pregnancies, makes improved criteria for finding the lesion clinically important.

As with many papers as I read them I have questions I wish I could ask the authors. I had trouble understanding how the placentas were selected. The N for the study is 156 “routine placentas”. They represented 11% of 1,471 “placenta cases”.  To me this could mean two different things. Either there were 156 placentas submitted to pathology from 1,471 placentas delivered, or 156 placentas were selected for the study presumably because they had been grossed by a specially trained pathology assistant and then evaluated by a board certified pediatric pathologist. There was no review of the clinical charts, and certainly no prospective attempt to obtain information about type of delivery, vaginal bleeding, length of third stage of labor, manual extraction, history of prior Cesarean deliveries, location of the placenta in the uterus. Some information however was provided based on the pathology requisition. Was there enough clinical information to exclude bias in which placentas were sent to pathology? For example, if all Cesarean sections, or manually removed placentas, or postpartum hemorrhage were sent to pathology, then the prevalence of either the evidence of an acute hemorrhage or of myofibers might be enhanced.  I was surprised that 21% of cases had “significant retroplacental blood and that 21cases (13.5%) had basal plate myofibers (some detected by actin). The authors describe clinical criteria as well as histological features, that suggest using an actin stain, but it was less clear how they had selected the individual cases. While I don’t think these questions (misreadings) of the paper would have any impact on the conclusions, would it not be helpful to be able to communicate directly with the authors and  have questions answered or points clarified. The authors likely have more information than they can impart in the confines of a formal paper.

I would also like the ability to have an open discussion of placenta accreta in general.  In my page on Chorioamnionitis, I organized it around naïve questions, and I think that is a good approach for out of the box discussion. For example, I have assumed that placenta accreta forms over an area without decidua and the chorion plate then attaches firmly to the muscle. As a result the placenta cannot be detached from the uterus (as it also can not be detached from the decidual tissue). What do we know about this gluing? I believe that fetal fibronectin and annexins are critical components. But how strong is this gluing? In classic cases of accreta with hysterectomy, the placenta remains adherent in some areas with the cleavage going through the placental tissue. How much force does it take to remove a placenta with cleavage through the myometrial layer without tearing the placenta?

How many patients with BPMF had risk factors that far exceed those of histological risk, such as placenta over an old C-section scar? What is the mechanism of accreta in those who do not have clinical risk factors?  Perhaps a plausible mechanism is that the implantation in some way destroys the underlying endometrium in some cases. How does this relate to the other histological lesions reported in the paper, which did not reach statistically significant correlations? Finally, with mechanical removal of the placenta in cases with accreta, why does the uterus not contract and stop the maternal hemorrhage?

Most important to me was that the article reminded me of the useful studies that could be accomplished if we worked as a large network of perinatal pathologists. A simple study would be to look at prior placentas from cases that had Cesarean hysterectomy specimens with confirmed placenta accreta. Any such study would want to collect some basic data on gravidity, prior Cesarean sections, and the gravid order of any placental pathology found. We would also want to keep track of the number of sections taken of the placental base. This study would be retrospective, with specific criteria for basal plate myofibers. The controls could be 2 placentas based on gestation and proximity to the index case. Slides could be blindly reviewed by other pathologists in the study, and questionable cases could be reviewed by all using digital images. The group could help navigate the administrative side such as IRBs and HIPPA in the USA. We might be able to find some funding for recuts and mailing, and find statistician help. The authors of the above paper might be the ones to initiate and coordinate it, or someone else who is so inspired.

I am just throwing out ideas.  Are there any others out there who think this might be a good idea? I suspect others might have different goals or structures for the group. I hope to hear from you.

(1) Wyand R., Cramer S. F., Oshri A., Heller D. S. Association of Retroplacental Blood with Basal Plate Myofibers. Pediatr Develop Pathol (2018) 21:371-379.