Connective tissue tumors.

Connective tissue consists of collagen, elastic fibers and ground substances produced by fibrocytes. These cells are usually spindle-shaped with slender nuclei and bipolar cytoplasmic extensions. Apart from labeling for vimentin and variable reactivity for factor XIIIa and CD34, fibrocytes are immunonegative. Electron microscopy reveals prominent endoplasmic reticulum, but is otherwise indistinct. Lesions with fibrocytic differentiation can be divided into five categories: scars, keloids, dermatofibromas, nodular fasciitis, and superficial fibromatoses are inflammatory lesions. Thereby, dermatofibromas and their subcutaneous/deep soft tissue counterpart nodular fasciitis can present with a wide variety of clinicopathologic variants which may be misinterpreted as malignancies. Prurigo nodularis, chondrodermatitis nodularis helicis, acanthoma fissuratum, and knuckle pads are hyperplasias; fibroma molle, fibrous papules, connective tissue nevi, and elastofibroma are hamartomas; and fibroma of tendon sheath, pleomorphic fibroma, and giant cell tumor of tendon sheath are benign neoplasms. Deep fibromatoses, dermatofibrosarcoma protuberans, giant cell fibroblastoma, giant cell angiofibroma, hyalinizing spindle cell tumor with giant rosettes, solitary fibrous tumor, myxofibrosarcoma, low-grade fibromyxoid sarcoma, acral myxoinflammatory fibroblastic sarcoma, and classical fibrosarcoma, are malignant neoplasms, that is fibrosarcomas of variable malignant potential. Lesions dominated by myocytes/ myofibroblasts, e.g. cutaneous myofibroma/infantile myofibromatosis, or by macrophages, e.g. xanthogranulomas, are not part of this chapter.