Unlike attempts at dating of contusions in which histological examination of the injuries has not been helpful, histological examination of abrasions in an attempt to determine their age is possible to a degree. Robertson and Hodge probably provide the most authoritative and logical method of approach.1
Figure 4.4. A. Postmortem ant bites simulating abrasions. B. Diaper rash (continued).
They describe four stages in the healing of abrasions:
1. Scab formation
2. Epithelial regeneration
3. Subepithelial granulation and epithelial hyperplasia
The first stage is scab formation. Serum, red cells, and fibrin are deposited on the abrasion. These are not used for aging, but do indicate survival following the injury. The infiltration of polymorphonuclear cells in a perivascular formation signifies that the injury is 4-6 h old. The earliest time for such a cellular reaction is 2 h, but it is usually not clearly visible until 4-6 h. By 8 h, the bed of the scab is marked by a zone of infiltrating polymorphonuclear cells underlying the area of epithelial injury. At 12 h, there are three layers: a surface zone of fibrin and red cells (or crushed epithelium in the case of impact abrasions), a deeper zone of infiltrating polymorphonuclear cells, and a layer of damaged abnormally staining collagen. For the next 12 to 18 h, the last zone is progressively infiltrated by polymorphonuclear cells.
The second stage is epithelial regeneration. Regeneration of the epithelial cells arises in surviving hair follicles and at the edges of the abrasion. Epithelial growth may appear as early as 30 h in superficial scrape-like abrasions and is clearly visible by 72 h in most abrasions.
The third stage is subepidermal granulation. This becomes prominent during days 5 to 8. It occurs only after epithelial covering of an abrasion. Perivascular infiltration and chronic inflammatory cells are now prominent. The overlying epithelium becomes progressively hyperplastic, with formation of keratin. This stage is most prominent during days 9 to 12 after injury.
The last stage is regression. It begins at about 12 days. During this phase, the epithelium is remodeled and becomes thinner and even atrophic. Collagen fibers, which began to appear in the late subepidermal granulation phase, are now prominent. There is a definite basement membrane and the vascularity of the dermis decreases.
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