What distinguishes a hypertrophic scar from a keloid?

Distinguishing Hypertrophic Scars from Keloids

In contrast to a keloid, a hypertrophic scar may subside spontaneously. 1, 2

Key Differences Between Hypertrophic Scars and Keloids

Clinical Boundaries and Growth Pattern

• Hypertrophic scars remain confined within the boundaries of the original wound, while keloids characteristically extend beyond the limits of the original injury 3
• Keloids demonstrate an invasive growth pattern with a tongue-like advancing edge underneath normal-appearing epidermis and papillary dermis, a feature not seen in hypertrophic scars 3

Natural Course and Resolution

• Hypertrophic scars may regress or subside spontaneously over time, typically within 12-24 months after injury 1, 2
• Keloids persist indefinitely and rarely show spontaneous regression 4, 2

Timing of Development

• Hypertrophic scars typically develop within weeks after injury 4
• Keloids may develop immediately after injury but can also appear months to years later 4
• Hypertrophic scars do not develop in delayed fashion years after the initial injury, unlike keloids 3

Genetic Predisposition

• Keloids show a stronger familial predisposition and genetic component compared to hypertrophic scars 4
• Keloids are more common in individuals with darker skin tones and show a clear genetic predisposition 2
• Hypertrophic scars are less likely to be familial and can occur in any skin type 3

Histopathological Differences

Collagen Organization

• Hypertrophic scars contain organized, parallel bundles of collagen that are oriented to the skin surface 3
• Keloids contain disorganized, large, thick collagen fibers randomly oriented to the epithelial surface 3
• Keloids uniquely display "keloidal collagen" (thickened hyalinized collagen), though this is only detectable in about 55% of keloid specimens 3

Specific Histological Features

• Hypertrophic scars typically show:

  • Flattening of the overlying epidermis
  • Scarring of the papillary dermis
  • Prominent vertically oriented blood vessels 3

• Keloids typically show:

  • No flattening of the overlying epidermis
  • No scarring of the papillary dermis
  • Horizontal cellular fibrous band in the upper reticular dermis
  • Prominent fascia-like fibrous band 3

Treatment Response

• Hypertrophic scars respond better to treatment modalities like pressure therapy, silicone gel sheeting, and intralesional corticosteroid injections 2
• Hypertrophic scars have lower recurrence rates after surgical excision compared to keloids 2
• Keloids often require more aggressive combination therapies including surgery with adjuvant radiation, cryotherapy, or interferon 1, 2

Clinical Implications

• The spontaneous regression potential of hypertrophic scars may influence treatment decisions, allowing for more conservative approaches in some cases 1
• Understanding the differences helps in patient counseling regarding prognosis and treatment expectations 2
• Misdiagnosis between the two conditions can lead to inappropriate treatment selection and poorer outcomes 3