Definition/General
Introduction:
Accessory lobe is a separate placental lobe distinct from the main placenta
It is connected by fetal blood vessels running through membranes
It represents a developmental variant of placentation
It is also known as succenturiate lobe.
Origin:
Results from secondary implantation sites during early pregnancy
Uneven distribution of trophoblastic tissue
Persistence of additional implantation
Geographic separation during placental development
Developmental anomaly of placentation.
Classification:
Classified by size: Small (<3 cm) vs Large (≥3 cm)
By number: Single vs multiple accessory lobes
By connection type: Vascular vs membranous attachment
Complete vs incomplete placental structure.
Epidemiology:
Incidence approximately 2-5% of pregnancies
More common in assisted reproductive technology
Underdiagnosed condition
Higher incidence with placental abnormalities
Often discovered postpartum.
Clinical Features
Presentation:
Retained placental tissue (major complication)
Postpartum hemorrhage
Vasa previa from connecting vessels
Preterm labor
Antepartum bleeding
Placental abruption (rare).
Symptoms:
Incomplete placental delivery
Continued postpartum bleeding
Signs of retained products of conception
Puerperal sepsis
Delayed uterine involution
Abnormal lochia.
Risk Factors:
In vitro fertilization
Advanced maternal age
Multiple gestation
Uterine abnormalities
Previous cesarean section
Placenta previa
History of placental abnormalities.
Screening:
Prenatal ultrasound (limited detection)
Careful placental inspection at delivery
Membrane vessel examination
Completeness assessment
Three-vessel cord verification.
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Gross Description
Appearance:
Well-formed separate placental mass
Connecting fetal vessels visible in membranes
Distinct fetal and maternal surfaces
Variable size from small to large
Normal placental architecture.
Characteristics:
Complete placental structure with chorionic and basal plates
Terminal villi present
Independent cotyledons
Vascular connections to main placenta
Normal placental consistency.
Size Location:
Size ranges 1-10 cm diameter
Located geographically separate from main placenta
Variable distance from main mass
Connected by membranous vessels
Any location in uterus.
Multifocality:
Usually single accessory lobe
Occasionally multiple lobes present
Various sizes
Different locations possible
Independent vascular supply.
Microscopic Description
Histological Features:
Normal placental histology
Appropriate villous maturation
Terminal villi with syncytiotrophoblast
Fetal capillaries present
Chorionic plate structures
Basal plate with decidua.
Cellular Characteristics:
Normal trophoblastic elements
Syncytiotrophoblast layer
Cytotrophoblast cells
Villous stromal cells
Hofbauer cells
Endothelial cells in fetal vessels.
Architectural Patterns:
Normal villous tree architecture
Appropriate branching pattern
Terminal villous development
Mature placental structure
Normal vascular distribution
Decidual interface.
Grading Criteria:
Assessment based on structural completeness
Maturation appropriateness
Vascular integrity
Size relative to main placenta
Functional capacity.
Immunohistochemistry
Positive Markers:
hCG (syncytiotrophoblast)
hPL (human placental lactogen)
CD34 (fetal endothelium)
Cytokeratin (trophoblast)
Factor VIII (endothelial cells)
Smooth muscle actin (vessel walls).
Negative Markers:
Pathological markers usually absent
Inflammatory markers (unless complications)
Neoplastic markers
Infectious organism stains.
Diagnostic Utility:
Confirms placental tissue
Demonstrates normal function
Rules out pathology
Vascular assessment
Maturation evaluation.
Molecular Subtypes:
Not applicable for routine classification
Functionally normal placental tissue
Same genetic makeup as main placenta.
Molecular/Genetic
Genetic Mutations:
No specific genetic mutations
Developmental anomaly
Normal chromosomal composition
Same genetics as main placenta
Epigenetic factors may influence development.
Molecular Markers:
Normal placental hormones
Appropriate growth factors
Normal enzyme expression
Functional metabolic markers
Vascular development markers.
Prognostic Significance:
Risk of retained placenta
Postpartum hemorrhage risk
Vasa previa complications
Good fetal outcomes if managed properly
Recurrence possible.
Therapeutic Targets:
Complete placental delivery
Manual examination of uterus
Removal of retained tissue
Prophylactic oxytocin
Careful monitoring postpartum.
Differential Diagnosis
Similar Entities:
Bipartite placenta (two equal main lobes)
Multilobed placenta
Placental cotyledon variations
Placental cysts
Hematomas
Umbilical cord cysts.
Distinguishing Features:
Accessory lobe: Separate smaller lobe
Accessory lobe: Vascular connections
Bipartite: Two equal-sized lobes
Bipartite: Division of main mass
Cotyledon: Part of main placenta.
Diagnostic Challenges:
Prenatal recognition difficult
Complete delivery assessment
Vascular connection identification
Differentiation from placental fragments
Size assessment.
Rare Variants:
Multiple accessory lobes
Large accessory lobe
Vasa previa with accessory lobe
Placenta previa with accessory lobe
Cord insertion to accessory lobe.
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 with accessory lobe measuring [size] cm, connected by fetal vessels through membranes
Diagnosis
Accessory Placental Lobe (Succenturiate Lobe)
Classification
Classification: [Single/Multiple] accessory lobe(s), [size category], with [vascular/membranous] connections
Morphological Features
Shows well-formed accessory placental lobe with normal architecture connected to main placenta
Vascular Connections
Fetal blood vessels connecting accessory lobe to main placenta identified in membranes
Histological Features
Accessory lobe shows normal placental histology with appropriate maturation for gestational age
Delivery Completeness
Placental delivery appears [complete/incomplete] with [no evidence/concern] of retained tissue
Clinical Significance
Risk factors include potential for retained placenta, postpartum hemorrhage, and vasa previa
Final Diagnosis
Accessory Placental Lobe, [characteristics], with [risk assessment] for postpartum complications