Trisomy 21-associated transient abnormal myelopoiesis involving the maternal space of the placenta: a case report and literature review

Criteria for placental examination for obstetrical and neonatal providers

Pathologic examination of the placenta can provide insight into likely (and unlikely) causes of antepartum and intrapartum events, diagnoses with urgent clinical relevance, prognostic information for mother and infant, support for practice evaluation and improvement, and insight into advancing the sciences of obstetrics and neonatology. Although it is true that not all placentas require pathologic examination (although alternative opinions have been expressed), prioritization of placentas for pathologic examination should be based on vetted indications such as maternal comorbidities or pregnancy complications in which placental pathology is thought to be useful for maternal or infant care, understanding pathophysiology, or practice modifications. Herein we provide placental triage criteria for the obstetrical and neonatal provider based on publications and expert opinion of 16 placental pathologists and a pathologists' assistant, formulated using a modified Delphi approach. These criteria include indications in which placental pathology has clinical relevance, such as pregnancy loss, maternal infection, suspected abruption, fetal growth restriction, preterm birth, nonreassuring fetal heart testing requiring urgent delivery, preeclampsia with severe features, or neonates with early evidence of multiorgan system failure including neurologic compromise. We encourage a focused gross examination by the provider or an attendant at delivery for all placentas and provide guidance for this examination. We recommend that any placenta that is abnormal on gross examination undergo a complete pathology examination. In addition, we suggest practice criteria for placental pathology services, including a list of critical values to be used by the relevant provider. We hope that these sets of triage indications, criteria, and practice suggestions will facilitate appropriate submission of placentas for pathologic examination and improve its relevance to clinical care.

Myeloid cell thrombus and fetal vascular malperfusion in placentas with transient abnormal myelopoiesis

Transient abnormal myelopoiesis (TAM), also known as transient myeloproliferative disorder or transient leukemia, is a self-regressing neoplasia that afflicts infants with trisomy 21. A recent review article documented "myeloid cell thrombus (MCT)" and "fetal vascular malperfusion (FVM)" in placentas with TAM, although the characteristic TAM placental findings have not been clarified. Here, we compared the clinical and pathological placental findings between trisomy 21 patients with or without TAM. In 13 cases of trisomy 21, we identified six placentas with TAM and seven placentas without TAM. The six placentas with TAM included two stillborn cases. Microscopically, MCT was noted in all the cases, and a high incidence of FVM (50%) was observed in TAM cases. Immunohistochemically, MCT was found to be a platelet-rich thrombus. The placentas were grouped according to the presence or absence of TAM and subsequently compared. Clinically, the incidences of abnormal fetal heart rate pattern and fetal or neonatal death were significantly higher in TAM cases. Pathologically, placenta in TAM cases weighted more than those in cases without TAM, and the incidence of MCT was significantly higher in placentas with TAM. Moreover, the incidence of FVM was higher in placentas with TAM, but this difference was not statistically significant. We propose that MCT is a diagnostic feature of placentas with TAM and may be associated with poor fetal outcomes.

Placental Pathology in Down Syndrome-Associated Transient Abnormal Myelopoiesis

Transient abnormal myelopoiesis is a hematopoietic disorder that occurs in up to 10% of neonates with Down syndrome. It is characterized by leukocytosis and the presence of circulating blast cells harboring truncating GATA1 mutations with variable multiorgan system involvement. Placental involvement of transient abnormal myelopoiesis is infrequently described. Placental examination and identifying features related to transient abnormal myelopoiesis could be one of the early, if not the only, means of diagnosis of this condition in affected stillbirths, premature infants, and a subset of asymptomatic neonates. This article provides an overview of the placental pathology in transient abnormal myelopoiesis with review of the literature, and also discusses the important differential diagnoses.

Extensive placental choriovascular infiltration by maturing myeloid cells in down syndrome-associated transient abnormal myelopoiesis

Transient abnormal myelopoiesis (TAM), a clonal proliferation of predominantly megakaryocytic precursor cells, affects 4%-10% of newborns with Down syndrome. Approximately 20%-30% of TAM survivors are at risk of development of acute myeloid leukemia (myeloid leukemia associated with Down syndrome, ML-DS). We report unusual placental findings in a female infant with trisomy 21 born at 38 weeks of gestation. In line with previous descriptions of placental pathology in infants with TAM, abundant blast-like cells were present in the lumen of chorionic and stem villous vessels. In addition, there was multifocal extensive infiltration of the wall of chorionic vessels by maturing myeloid cells in a pattern reminiscent of TAM- or leukemia-associated systemic infiltration. The clinical significance of this unusual choriovascular involvement of the placenta in TAM is undetermined.