Pathologically diagnosed superficial form of placenta accreta: a comparative analysis with invasive form and asymptomatic muscular adhesion

Pathologically diagnosed placenta accreta is defined as villi adjacent to the myometrium without decidua. It is classified into the superficial (placental accreta vera [PAV]) and deep invasive (placenta increta [PI] and placenta percreta [PP]) types. Data on the clinicopathological characteristics of PAV are limited. Basal plate myometrium (BPMYO) is found in PAV or placentas in asymptomatic women, but its significance is still controversial. This retrospective study aimed to determine the clinicopathological characteristics of pathologically diagnosed PAV and the significance of BPMYO. We reviewed 84 cases of pathologically diagnosed placenta accreta (PAV, 54; PI, 16; and PP, 14), and compared them with controls (i.e., not pathologically diagnosed of any type of placenta accreta, n = 51). Among the PAV cases, the incidence of in vitro fertilization was high, while that of previous cesarean section or placenta previa was low. The incidence of maternal complications was also high in pathologically diagnosed PAV cases, but some PAV were asymptomatic. The rate of prenatal diagnosis of PAV was low, and a high proportion of patients required emergency transportation to central hospitals. Histologically, BPMYO was found in 7 (14%) of controls and 54 (100%) of PAV cases. PAV cases had a higher rate of advanced stages of BPMYO, larger muscle tissue, and more foci than controls. In conclusion, almost PAV is a clinically symptomatic condition but has distinct risk factors and clinical findings from advanced type placenta accreta. Histological evaluation of BPMYO is useful for the diagnosis of PAV.