Panniculitis - Definition of terms and diagnostic strategy

Inflammation of the subcutaneous tissue represents a dynamic process that s hows different histopathologic findings at different stages of development; therefore, the stage of evolution of a lesion at the time of biopsy influe nces the microscopic appearance significantly. Furthermore, location and ty pe of inflammation may vary among different examples of the same panniculit is independent of the stage of evolution. For these reasons, the histopatho logic diagnosis of panniculitides is often difficult. Currently, the most c ommon approach to diagnosis is differentiation between predominantly septal and predominantly lobular panniculitis, followed by the distinction betwee n lesions with and without vasculitis. Although these criteria are importan t for diagnosis, they are often insufficiently specific. To determine an al ternative method of diagnosis, 329 cases of panniculitis were histopatholog ically analyzed using the following parameters: location and type of inflam matory infiltrate within and around the subcutaneous tissue, presence or ab sence of fat necrosis, type of necrosis, presence or absence of vascular ch anges, and presence or absence of associated findings (e.g., hemorrhage, sc lerosis). On the basis of the results of this study and of an extensive rev iew of the literature, tables of histopathologic findings for the diagnosis of panniculitides are presented.