Abstract
During the hemostasis stage of the wound healing process, fibroblasts on abnormal
scar tissue have difficulty in mediating fibrinolysis because they exhibit an intrinsically low level of plasminogen activator and a high level of the inhibitor activity.
The result is a lower plasmin concentration and an inferior breakdown of fibrin
(10). Fibroblasts in excessive scar tissue show normal growth parameters but
produce abnormal amounts of extracellular matrix (11). In keloid-derived
fibroblasts, fibronectin production is increased (12), and its activity continues at high
level for months to years in hypertrophic scars and keloids (13,14). Fibronectin
concentration is higher mainly in perivascular areas and in the collagen nodule of
the
Table 1 Clinical and Diagnostic Comparison of Hypertrophic Scars and Keloids
Hypertrophic scars Keloids
Early appearance
(within 4weeks after
original injury)
May take months to years to appear
after original injury
May have spontaneous regression
(within 12-18months) (3)
Tendency to persist
Surgery indicated as a treatment
(Z-plasties)
Recur after surgery
(50% of the time)
Located on flexor surfaces more
often than extensor areas
Located on earlobes, anterior chest, cheeks,
among others, and rarely involves the joints
Remain limited to the boundaries
of the initial site of injury (4)
Extend beyond the
original wound
Light microscopy findingsa: large
nodules containing cells and
collagen within the mid-to-deep
part of the scar
(collagen nodule) (3)
Light microscopy findingsa: large
collagen bundles, less oriented
compared with hypertrophic scars.
Abundant eosinophils,
mast cells, plasma cells, and
lymphocytes (3,18)
Electron microscopy findings:
collagen fibers are smaller,
more regular, and have
higher interfibrillar distance
compared with keloids (2)
Electron microscopy findings:
presence of large, broad
bundles of pink collagen
separated by an amorphous
ground substance (5)
Higher metabolic activity
and less degradation
of newly synthesized collagen proteins (6)
Higher expression of proliferating
cell nuclear antigen (7)
Complications: contractures and
possible loss of function
and restriction of movement
if overlying a joint
Complications: tenderness, pain, burning,
and pruritus (found to be the
most common symptom in an
earlier survey) (11)
granulation-tissue formation, persist in hypertrophic scars after the wound is fully
epithelialized (8). This may be important in the pathogenesis of scar contracture,
seen exclusively in hypertrophic scars. During the transition between granulation
tissue and scar formation, keloid fibroblasts may undergo apoptosis, at a rate lower
than fibroblasts found in normal scars (see Sec. 3.3.4).