Answer: B - Cellular Neurothekeoma

Cellular neurothekeoma is often diagnosed in children or young adults and presents as a solitary slow-growing mass, typically less than 2 cm.  It is a dermal-based lesion that occasionally extends to subcutis. It often affects the head and neck region or the extremities, but it has been also been reported in a variety of other sites. 

Cellular neurothekeoma is an uncommon mesenchymal proliferation with uncertain lineage. Typically, it has a lobulated histological pattern with spindled to epithelioid cytomophology.  Lesional cells have round to ovoid, large to medium-sized nuclei with fine chromatin and pale to eosinophilic cytoplasm. Cellular aggregates with fascicular configuration are separated by thin or hyaline fibrous septa.  About a third of cellular neurothekeomas have myxoid areas and a minority also contain osteoclastic giant cells.  Variable levels of cytologic atypia and brisk mitotic activity can be seen, although these features do not predict poor prognosis or aggressive behavior in these tumors. It is imperative to exclude other tumors with similar morphology, such as spitzoid melanocytic lesions or fibrohistiocytic tumors, by immunohistochemical means, before a diagnosis of cellular neurothekeoma is established.   Cellular neurothekeoma is a benign lesion and conservative, adequate removal is often curative.  

Cellular neurothekeoma is generally positive for neuron-specific enolase, vimentin, CD10 and PGP9.5.  It can be positive for MiTF, but it is negative for S100 and melanocytic markers such as Melan-A, SOX10, and HMB 45.  It may show weak staining with CD68 and focal staining with smooth muscle actin.

1. Fetsch, John F et al. “Neurothekeoma: an analysis of 178 tumors with detailed immunohistochemical data and long-term patient follow-up information.” The American journal of surgical pathology vol. 31,7 (2007): 1103-14.

2. Hornick, Jason L, and Christopher D M Fletcher. “Cellular neurothekeoma: detailed characterization in a series of 133 cases.”The American journal of surgical pathologyvol. 31,3 (2007): 329-40.