Résumé
Acquired perforating dermatosis is a group of disease characterized by transepidermal elimination of altered dermal constituents of unknown pathogenesis. The giant variant was first described in 2006, as an emerging entity with seven reported cases to date. Here is an 83-year-old male presented with a 4-year history of gradually enlarging soft tisssue mass with ulcerartions at the left knee joint. Imaging revealed an extra-articular, single, heterogeneous, multinodular mass, suspicious for a soft tissue sarcoma. Wide local excision of the mass showed fleshy, hemorrhagic nodules communicating with epidermal ulcers. Microscopy showed cystic spaces straddling dermis and subcutis, containing eosinophilic, amorphous, granular material extruding through epidermal craters, surrounded by exuberant myofibroblastic proliferation. Trichrome and van-Gieson stains confirmed that the extruded material is collagen and the histology was compatible with the giant variant of acquired perforating collagenosis. Awareness of histological appearance prevents misdiagnosis and overtreatment of this entity, masquerading as a sarcoma clinically.