Definition/General
Introduction:
Placental accreta is the abnormal adherence of the placenta to the uterine wall due to absence or deficiency of the decidua basalis
The chorionic villi attach directly to the myometrium
It occurs in 0.04-0.9% of pregnancies
The incidence is increasing due to rising cesarean section rates
It is a major cause of postpartum hemorrhage.
Origin:
Results from defective decidualization at the implantation site
Often associated with previous uterine surgery
Endometrial scarring leads to poor decidual formation
Trophoblast invasion proceeds deeper than normal
May be related to placental location over previous scar.
Classification:
Part of accreta spectrum disorders: Accreta vera (attachment to myometrium)
Increta (invasion into myometrium)
Percreta (invasion through myometrium)
Graded by depth of invasion
May be focal or diffuse.
Epidemiology:
Incidence: 0.04-0.9% overall
Risk with placenta previa and prior cesarean: 3-67%
Maternal mortality: 6-7%
Hysterectomy rate: 40-50%
20-fold increase over past 50 years
Associated with advanced maternal age.
Clinical Features
Presentation:
Retained placenta after delivery
Postpartum hemorrhage
Failed manual removal of placenta
Incomplete placental delivery
May be asymptomatic until delivery
Shock from blood loss.
Symptoms:
Heavy bleeding after delivery
Inability to deliver placenta
Continued bleeding despite uterotonic agents
Hemodynamic instability
Abdominal pain
Signs of shock.
Risk Factors:
Previous cesarean section (strongest risk factor)
Placenta previa
Advanced maternal age (>35 years)
Multiparity
Previous uterine surgery (myomectomy, D&C)
Asherman syndrome
Endometrial ablation
Smoking.
Screening:
Prenatal ultrasound findings: loss of retroplacental clear zone
Bladder wall irregularity
Lacunar flow on Doppler
MRI for suspected percreta
Multidisciplinary planning essential.
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Gross Description
Appearance:
Placenta firmly adherent to uterine wall
No cleavage plane between placenta and myometrium
Myometrial fibers attached to placental surface
Areas of incomplete separation
Hemorrhagic, ragged maternal surface.
Characteristics:
Irregular maternal surface with adherent myometrium
Absence of decidua in affected areas
Direct villous-myometrial contact
Fibrous tissue replacement
Vascular congestion.
Size Location:
May involve entire placenta or be focal
Commonly affects lower uterine segment
Anterior wall involvement common with cesarean scars
May extend to lateral walls.
Multifocality:
Multiple areas of abnormal adherence
Skip lesions with normal areas
Progressive involvement possible
Associated with other placental abnormalities.
Microscopic Description
Histological Features:
Chorionic villi in direct contact with myometrium
Absence of decidua basalis
Extravillous trophoblast invasion into muscle
Fibrous tissue between villi and muscle
Chronic inflammation may be present.
Cellular Characteristics:
Trophoblast cells infiltrating myometrial bundles
Syncytiotrophoblast directly apposed to muscle fibers
Intermediate trophoblast within myometrium
Absence of decidual cells
Fibroblast proliferation.
Architectural Patterns:
Loss of decidual architecture
Villous-myometrial interface abnormal
Irregular trophoblast distribution
Fibrous septa formation
Vascular abnormalities.
Grading Criteria:
Accreta: Villi attached to myometrium
Increta: Villi invade myometrium
Percreta: Villi through full thickness
Focal vs diffuse involvement
Depth of invasion assessment.
Immunohistochemistry
Positive Markers:
Cytokeratin (trophoblast identification)
Inhibin-α (trophoblast marker)
Mel-CAM (extravillous trophoblast)
hPL (placental lactogen)
Smooth muscle actin (myometrium).
Negative Markers:
CD45 (excludes inflammatory cells)
CD68 (excludes macrophages)
Desmin may be decreased in involved myometrium.
Diagnostic Utility:
Trophoblast markers demonstrate invasion depth
Smooth muscle markers outline myometrial bundles
Helps distinguish accreta from increta/percreta
Useful in hysterectomy specimens.
Molecular Subtypes:
Focal accreta (limited area)
Diffuse accreta (extensive involvement)
Associated with previa
Scar-related accreta.
Molecular/Genetic
Genetic Mutations:
No specific mutations identified
PTEN expression may be altered
β-catenin pathway abnormalities
Matrix metalloproteinase dysregulation.
Molecular Markers:
Decreased PTEN expression
Increased MMP-9
Altered integrin expression
Abnormal E-cadherin
Vascular markers (VEGF, PlGF).
Prognostic Significance:
Depth of invasion determines management
Associated hemorrhage risk
Need for hysterectomy
Future pregnancy risks
Recurrence in subsequent pregnancies.
Therapeutic Targets:
Conservative management options
Uterine artery embolization
Balloon occlusion
Methotrexate in selected cases
Hysterectomy definitive treatment.
Differential Diagnosis
Similar Entities:
Placental increta (deeper invasion)
Placental percreta (full-thickness invasion)
Retained placenta (normal adherence)
Uterine atony
Coagulopathy.
Distinguishing Features:
Accreta: Surface attachment only
No myometrial invasion
Increta: Invasion into myometrium
Deeper trophoblast
Percreta: Through full thickness
Serosal involvement.
Diagnostic Challenges:
Distinguishing severity levels
Focal vs diffuse disease
Intraoperative diagnosis
Frozen section limitations
Clinical correlation essential.
Rare Variants:
Accreta with normal decidua elsewhere
Skip lesions
Associated with uterine anomalies
Extracorporeal accreta.
Sample Pathology Report
Template Format
Sample Pathology Report
Complete Report: This is an example of how the final pathology report should be structured for this condition.
Specimen Information
[Placenta/Hysterectomy specimen] with abnormal placental adherence
Diagnosis
Placental accreta vera
Clinical History
Retained placenta, postpartum hemorrhage, [risk factors]
Gross Findings
Placenta firmly adherent to uterine wall, no cleavage plane, myometrial tissue attached
Microscopic Findings
Chorionic villi in direct contact with myometrium, absent decidua basalis
Extent of Involvement
[Focal/Diffuse] involvement of [X]% of placental-uterine interface
Invasion Depth
Trophoblast invasion limited to myometrial surface (accreta vera)
Associated Findings
Hemorrhage, inflammation, fibrous tissue replacement
Management Implications
Risk of hemorrhage, may require [conservative/surgical] management
Final Diagnosis
Placental accreta vera, [focal/diffuse]