Definition/General
Introduction:
Umbilical cord knots are mechanical complications classified as true knots or false knots
True knots occur in 0.3-2% of pregnancies and represent actual knotting of the cord
False knots are localized swellings without actual knotting
True knots can cause significant perinatal morbidity and mortality.
Origin:
True knots result from fetal movement through cord loops during early pregnancy
Require adequate amniotic fluid and cord length
Small fetal size facilitates passage through loops
False knots result from vessel length discrepancy or Wharton's jelly accumulation.
Classification:
Classified as true knots (actual knotting) or false knots (pseudo-knots)
Loose knots versus tight knots
Single knots versus multiple knots
Simple knots versus complex knots.
Epidemiology:
True knots: 0.3-2% of pregnancies
False knots: more common (5-10%)
Higher incidence with polyhydramnios
More common in long cords
Associated with increased fetal mortality (4-10 fold).
Clinical Features
Presentation:
Variable fetal heart rate patterns
Fetal distress during labor
Decreased fetal movements
Intrauterine growth restriction
Stillbirth (in tight knots)
Meconium-stained liquor.
Symptoms:
Bradycardia or variable decelerations
Abnormal cardiotocography
Cord compression signs
Emergency cesarean section indication
Intrauterine fetal death
Neonatal complications.
Risk Factors:
Polyhydramnios
Long umbilical cord (>70 cm)
Male fetal gender
Advanced gestational age
Multiparity
Small fetal size for gestational age.
Screening:
Ultrasound detection possible but challenging
Cord imaging with color Doppler
Fetal monitoring during labor
Amniotic fluid volume assessment
Cord length estimation.
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Gross Description
Appearance:
True knots show actual cord knotting with crossing loops
Tight knots may show constriction
Loose knots easily manipulated
False knots appear as localized swellings
Color changes if vascular compromise.
Characteristics:
Vessel compression at knot site
Congestion distal to tight knots
Edema or hemorrhage possible
False knots show vessel redundancy
Wharton's jelly accumulation in false knots.
Size Location:
Location: any cord segment
Middle third most common for true knots
Size varies with tightness degree
Cord length usually increased
Distance from fetal/placental end variable.
Multifocality:
Usually single knot
Multiple knots rare (<0.1%)
May be associated with cord coiling abnormalities
Other cord anomalies possible.
Microscopic Description
Histological Features:
True knots show vessel compression and distortion
Vascular congestion or collapse
Thrombosis may be present
Wharton's jelly compression
False knots show vessel redundancy without compression.
Cellular Characteristics:
Endothelial damage in compressed vessels
Smooth muscle changes
Inflammatory infiltrate if severe compression
Fibroblast alterations
Red blood cell extravasation.
Architectural Patterns:
Severe vessel architectural distortion
Loss of normal vessel relationships
Perivascular changes
Wharton's jelly compression or edema
Focal necrosis in tight knots.
Grading Criteria:
Assessment of knot tightness
Vessel compression degree
Thrombosis presence
Inflammatory response
Tissue viability.
Immunohistochemistry
Positive Markers:
CD31 highlights vessel endothelium
CD34 in vascular structures
Smooth muscle actin in vessel walls
Factor VIII in endothelium
Fibrin stains if thrombosis.
Negative Markers:
Cytokeratin negative in vessels
No specific negative markers
Normal vascular immunophenotype
Inflammatory markers variable.
Diagnostic Utility:
Assesses vessel integrity
Identifies endothelial damage
Confirms vascular nature
Thrombosis detection
Research applications.
Molecular Subtypes:
No specific molecular classification
Hypoxia markers in tight knots
Stress response proteins
Apoptosis markers in severe cases.
Molecular/Genetic
Genetic Mutations:
No specific genetic associations
Connective tissue variants possible
Cord development genes may be involved
No familial clustering reported
Random mechanical event.
Molecular Markers:
Hypoxia-inducible factors upregulated in tight knots
Inflammatory mediators
Stress response proteins
Apoptosis pathways activated
Vascular injury markers.
Prognostic Significance:
Tight knots associated with poor outcomes
Loose knots often asymptomatic
Fetal mortality increased 4-10 fold
Emergency delivery often required
Neonatal complications possible.
Therapeutic Targets:
No preventive measures available
Enhanced monitoring during labor
Emergency delivery preparedness
Neonatal resuscitation readiness
Counseling for future pregnancies.
Differential Diagnosis
Similar Entities:
False knots (pseudo-knots)
Cord loops
Cord coiling abnormalities
Cord hematoma
Focal cord edema.
Distinguishing Features:
True knot: actual knotting with crossing
True knot: vessel compression
False knot: localized swelling
False knot: no vessel crossing
Loops: no knotting
Hematoma: blood products.
Diagnostic Challenges:
Distinguishing true from false knots
Tightness assessment
Clinical significance evaluation
Postmortem changes consideration
Documentation requirements.
Rare Variants:
Multiple true knots
Complex knots
Knots with cord rupture
Sliding knots
Knots in short cords.
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
Umbilical cord measuring [X] cm with knot at [location]
Knot Classification
Knot type: [true/false] knot, [loose/tight] configuration
Knot Location
Location: [X] cm from [fetal/placental] end, [segment] of cord
Vessel Examination
Vessels at knot site: [normal/compressed/congested], [present/absent] thrombosis
Tightness Assessment
Knot tightness: [loose/moderately tight/tight], [present/absent] vascular compromise
Microscopic Findings
Microscopy shows [normal/compressed] vessel architecture with [present/absent] ischemic changes
Clinical Significance
Clinical significance: [risk assessment] based on knot tightness and vessel compromise
Final Diagnosis
[True/False] umbilical cord knot, [loose/tight]