Keloid and Hypertrophic Scars: Comparative Histopathological and Immunohistochemical Study

Keloids and hypertrophic scars are different expressions of the same derailment of wound healing; their biological behaviors and appearances are quite different. The clinical differences between hypertrophic scars and keloids have long been recognized. However, distinguishing between the two types of scars on histology is sometimes difficult as the ‘keloid collagen’, the hallmark of keloid, is not always present. Plus the α-smooth muscle actins, a differentiating marker of hypertrophic scar is variably expressed in both forms of scars. The present study is an attempt to reinforce the validity of existing criteria and to investigate additional distinguishing features to facilitate the distinction between these two entities. The morphological features and the expression of α-smooth muscle actins in myofibroblasts in the two conditions have been investigated. These results demonstrate that keloids are characterized by the presence of collagen fibers, which are abnormally large, dense, broad, glassy, eosinophilic, focally fragmented complexes, arranged haphazardly and packed together by “keloid collagen”. In contrast hypertrophic scars exhibit collagen, which is discretely nodular, fibrillar with fairly regular thickness of fibers with its long axis parallel to the epidermis. It was confirmed that such nodular structures are always present in hypertrophic scar and rarely in keloid. Furthermore, keloid scars occasionally show myofibroblasts expressing α-smooth muscle actins, while hypertrophic scars are negative for α-smooth muscle actins.