Table 1 Hypertrophic scars and keloids: epidemiological, clinical and histological differences.

Incidence

40% to 70% following surgery, up to 91% following burn injury Equal in sex distribution with highest incidence in the second to third decade

6% to 16% In African populations

Predilection sites

Shoulders, neck, presternum, knees and ankles Less affected: eyelids, cornea, palms, mucous membranes, genitalia and soles

Anterior chest, shoulders, earlobes, upper arms and cheeks

Time course

Within 4 to 8 weeks following wounding, rapid growth phase for up to 6 months, then regression over a period of a few years Low recurrence rates after excision of the original hypertrophic scar

Within years after minor injuries or spontaneous formation on the midchest in the absence of any known injury. Persistence for long periods of time. No spontaneous regression High recurrence rates following excision

Appearance

Do not extend beyond the initial site of injury

Projects beyond the original wound margins

Histological characteristics

Primarily fine, well-organized, wavy type III collagen bundles oriented parallel to epidermis surface with abundant nodules containing myofibroblasts and plentiful acidic mucopolysaccharide. Proliferating cell nuclear antigen (PCNA)/p53-level/ATP expression low

Disorganized, large, thick, type I and III hypocellular collagen bundles with no nodules or excess myofibroblasts. Poor vascularization with widely scattered dilated blood vessels. PCNA/p53-level/ATP expression high