Annals of diagnostic pathology
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Benign peripheral nerve sheath tumors (PNSTs) showing more than one line of differentiation (hybrid PNSTs) have been increasingly recognized, mainly due to awareness of their existence and as a consequence of increased use of immunohistochemisty during the last decade. Two recent studies suggested overrepresentation of hybrid tumors among benign PNSTs in patients with neurofibromatosis type 1 (NF-1). This study was performed to assess the presence of perineurial cells in microscopic (early) neurofibromatous lesions and normal-looking peripheral nerves in specimens from 5 patients with NF-1 using markers of perineurial cell differentiation (epithelial membrane antigen, claudin-1, and glucose transporter 1). ⋯ Both patients had concurrent multiple larger PNSTs (plexiform neurofibromas, hybrid neurofibroma/perineurioma and lesions with features intermediate between the 2 types). One specimen harboring high-grade malignant PNST and 2 specimens with large solitary neurofibromas displayed no intraneural perineurial cells. These observations suggest that intraneural perineurial proliferations are part of the early lesions in the setting of constitutional NF-1 inactivation and support the concept of pure and hybrid perineuriomatous lesions as novel member of the spectrum of PNSTs in NF-1.