SPTCL : Morphology
Morphology of Subcutaneous panniculitis-like T-cell lymphoma (SPTCL): The neoplastic cells are localized to the subcutaneous fat in a pattern resembling lobular panniculitis. They are almost never seen in other sites/locations. There may be some spread into the deep reticular dermis, but the superficial dermis and epidermis are not involved (i.e. no epidermotropism). There is no angiodestruction or angioinvasion. The neoplastic cells are pleomorphic, mostly small to medium-sized cells with occasional large cells. They have hyperchromatic nuclei and scant cytoplasm. They are arranged singly or in small nests around individual adipocytes. This so-called rimming of adipocytes is not unique to SPTCL and can be seen with virtually all lymphomas involving the subcutaneous fat as well as with reactive infiltrates. Additional findings in SPTCL include fat necrosis, karyorrhexis, histiocytic infiltrates (with phagocytized nuclear debris), erythrophagocytosis, and granulomas. Occasional reactive lymphocytes may be present. Plasma cells and lymphoid follicles are rare, except in cases with overlapping features of lupus erythematosus panniculitis.