Perineurial cell differentiation in neurofibromas. Report of eight cases including a case with composite perineurioma-neurofibroma features

Among 99 cases of neurofibroma (NF), eight tumors (8%) contained epithelial membrane antigen (EMA)positive perineurial cells inside the lesions. These cells were numerous and represented a significant part of the tumor cell p opulation. In case 7, EMA-positive cells represented approximately half of the tumor. These patients' ages ranged from 23 to 73 years (average 51 year s). Six patients were females and two were males. Neurofibromatosis type I was present in one case. The histological types of neurofibromas with EMA-p ositive cells were as follows: cutaneous, well-circumscribed, localized typ e in four cases; cutaneous diffuse type in one case; subcutaneous, well-cir cumscribed type in two cases; and subcutaneous plexiform type in one case. Perineurial cell differentiation was suspected by examining routinely stain ed sections in four cases; it was unsuspected in four cases. The perineuria l cells were arranged in a pattern similar to that of "pure" perineurioma. They possessed thin bipolar processes and were arranged in laminar fascicle s and whorls. In cellular areas, the cytoplasm was more eosinophilic and ce ll borders were poorly visible. In contrast, when the stroma was myxoid, it accentuated the shape of individual cells. As these morphological features of perineurial cell differentiation in NF are not entirely specific, EMA s taining is recommended to prove the perineurial cell differentiation in neu rofibromas. An additional immunohistochemical result of this study is the p resence of numerous CD34-positive cells in all neurofibromas, which is simi lar to previous studies.