Placenta Accreta Spectrum: Evaluation of classic and non-classic presentations, pathologic grading, and uterine scar dehiscence features in a modern institutional series

Introduction: The aim of this study is to document the distribution of classic versus non-classic presentation of Placenta Accreta Spectrum (PAS) disorders as well as grading categories by the Society for Pediatric Pathology (SPP) and FIGO systems in an institutional cohort of gravid hysterectomies. We also document the prevalence of uterine scar as a histologic correlate for uterine scar dehiscence, a phenomenon raised by some as central to PAS pathogenesis. Methods: PAS cases were assigned grade and designated as classic (anterior lower uterine segment implantation, prior C-section) or non-classic (implantation away from anterior lower uterine segment and/or no prior C-section). Features of dehiscence (uterine window, histologic evidence of scar) were recorded. Results: Sixty-two patients were included: 76 % had prior C-section; 55 % had other forms of uterine instrumentation. Classic PAS was recorded in 52 % patients; notably, 48 % had non-classic presentation; of these, all but one had prior instrumentation (curettage, myomectomy, laparoscopy). Uterine window was described in 53 % classic and 23 % non-classic PAS. Scar was demonstrated in 31 % classic and 23 % non-classic PAS; trichrome/ reticulin stains were confirmatory. 32 % cases were SPP grade 1, 18 % grade 2, 18 % grade 3a and 32 % grade 3d. Grade 3 was significantly more common in classic (72 %) than non-classic (27 %) PAS. Discussion: While most PAS patients have classic presentation, a large subset does not; in addition, scar tissue is not identified histologically in most PAS hysterectomies; in these settings, PAS cannot be fully attributed to scar dehiscence. Uterine instrumentation often precedes non-classic PAS reinforcing the concept of decidual disruption as central to PAS pathogenesis. PAS grading as defined correlates with presentation (classic vs nonclassic).