Solitary sclerotic fibroma of the skin: a sclerotic dermatofibroma?

Two cases of solitary tumors showing well-demarcated hypocellular, dermal fibrocollagenous proliferations are reported. The lesions were composed of hyalinized eosinophilic collagen bundles arranged in the characteristic interwoven pattern with prominent clefts, as described in sclerotic fibroma of the skin. This pattern, although predominant, was not uniform. Some areas showed a more cellular pattern with histopathologic features suggestive of dermatofibroma. In those areas, multiple spindle-shaped cells and occasional multinucleated cells were observed. The collagen bundles did not adopt a whorled pattern, and the overlying epidermis showed mild acanthosis and elongation of the rete ridges. The sclerotic changes were present mainly at the periphery and in the deep areas of the tumor. Our observations confirm the possibility that solitary sclerotic fibroma of the skin may represent, at least in some instances, the later and sclerotic stage of other more cellular neoplasms (specifically dermatofibromas) rather than an individualized neoplasm, as has been recently proposed.