A 29 years old female presented an intradermal nodular lesion on the left arm. Clinical impression was a dermatofibroma. Otherwise, medical history is unremarkable. Initially a shave biopsy was performed and after histological evaluation of the initial biopsy, a complete excision has been recommended and performed.
The initial shave biopsy showed interstitial infiltration of large epithelioid cells in the dermis sparing the epidermis. The tumor cells dissected dermal thickened collagen fibers and showed indistinct cytoplasmic membranes and glassy ample eosinophilic cytoplasm, some of them mimicking gemistocytes. The nuclei are large and bubbly with prominent purple nucleoli. The overall findings of infiltrative growth, nuclear atypia, and mitosis raised concern if this was a malignancy. Therefore, the histological evaluation of the entire lesion has been recommended. The entire lesion excised later showed multinodular pattern of epithelioid and spindled cell proliferation forming nests and fascicles infiltrating into the deep dermis and superficial subcutis. The epithelioid tumor cells showed similar histological features of those found in the initial biopsy. The cytological atypia and mitosis were present. Myxoid stroma was not noted. Patch chronic inflammatory cell infiltrate was seen. Immunohistochemical studies showed that the tumor cells were positive for NKI-C3 and MiTF and negative for S-100 (on initial biopsy), CD68 (on initial biopsy) and factor XIIIa (on initial biopsy). Immunophenotype supported the diagnosis of neurothekeoma.