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Benign cutaneous plexiform hybrid tumor of perineurioma and cellular neurothekeoma on the leg

Dear Editor, Benign cutaneous plexiform hybrid tumor of perineurioma and cellular neurothekeoma (BCPHTPCN) is a rare subcutaneous tumor and was histologically described for the first time in 2013.1 Until now, 12 cases had been reported and they exhibited mixed immunohistopathological features of perineurioma and cellular neurothekeoma arranged in a plexiform architecture with unknown origin.1– 4 They typically locate on the facial area except one possible case of BCPHTPCN that showed atypical histological appearance without plexiform architecture on the ankle.2 Herein, we report a case of BCPHTPCN arranged in a typical plexiform architecture outside the facial areas. A 73yearold healthy male developed a welldefined, reddish, 10mm, pruritic nodule on his right thigh that he had been aware of for 3 months (Figure 1a,b). We performed local excision and hematoxylin– eosin (HE) staining showed a wellcircumscribed but not encapsulated dermal nodule without connection to the epidermis. The neoplastic cells were arranged in fascicular and plexiform manner (Figure 1c,d). Among them, some parts of neoplastic cells were arranged in round nests or fascicular pattern which had relatively abundant pale eosinophilic cytoplasm with ovalshaped nuclei and nuclear bodies called pinpoint nucleoli (Figure 1e). These characteristics are consistent in part with cellular neurothekeoma. To confirm our diagnosis, we performed immunohistochemical staining for several neuromarkers of antibodies. Immunohistochemically, microphthalmiaassociated transcription factor (Figure 1f) and NKI/ C3 were positive, which were consistent with cellular neurothekeoma. On the other hand, positive results for epithelial membrane antigen (EMA) (Figure 1g), glucose transporter 1 (GLUT1) (Figure 1h), CD10, and PGP9.5 were consistent with perineurioma. In addition to that, positive results for EMA and GLUT1 and negative result for neuronspecific enolase (NSE) are not typically seen in cellular neurothekeoma. The results of HE staining and immunohistochemical staining led to the diagnosis of a hybrid tumor of cellular neurothekeoma and perineurioma. Benign cutaneous plexiform hybrid tumor of perineurioma and cellular neurothekeoma is literally a benign hybrid tumor that has a histologically plexiform arrangement of neurothekeoma and perineurioma.1 HE staining of our case demonstrated a histological characteristic of BCPHTPCN. In addition, immunohistochemical staining showed that the staining pattern except for NSE was consistent with most of the previously reported immunohistochemical characteristics of BCPHTPCN. Although the inconsistency of immunohistochemical patterns of NSE, three of the nine reported cases were negative for NSE. Therefore, we considered that the staining pattern of our case was consistent with BCPHTPCN.1,2,3,4 Thus far, previous BCPHTPCN occurred in the facial area (especially in the perioral region) with the exception of one case arising from the ankle.2 But the ankle case did not exhibit typical pathological features of BCPHTPCN because of a lack of plexiform structures, suggesting the possibility that BCPHTPCN developing outside the face may not exhibit typical pathological appearances; however, our case clearly demonstrated typical pathological presentation. To the best of our knowledge, this is the first case report of BCPHTPCN outside the facial area with typical plexiform architectures.