Dendritic cell neurofibroma with pseudorosettes - A report of 18 cases of a distinct and hitherto unrecognized neurofibroma variant

The authors present 18 cases of a hitherto unrecognized variant of cutaneou s neurofibroma. The tumors presented in adults (10 occurred in men and eigh t occurred in women) as a solitary, well-circumscribed, superficial lesion located in the dermis measuring 3 to 17 mm (mean size, 6.2 mm). The tumors formed oval-shaped masses that ran perpendicular to the epidermis. In the d eep pan of the tumor there was multinodular arrangement with two types of c ells: Type I cells were small, dark, lymphocyte-like cells with a slightly irregular nucleus and inconspicuous cytoplasm. Type II cells were larger, w ith pale-staining vesicular nuclei, with frequent invaginations and intranu clear inclusions, and had copious clear eosinophilic cytoplasm that formed a stellate growth pattern, which was poorly visible on hematoxylin and eosi n staining. Type I cells were grouped concentrically around type II cells a nd formed pseudorosettes. Most of the type I and type Ii cells were S-100 p rotein and CD57 positive, and various proportions of both cell types were C D56 and PGP9.5 positive. All cells were chromogranin A, synaptophysin, glia l fibrillary acidic protein, cytokeratins, CD1a, CD21, CD31, alpha -smooth muscle actin, muscle-specific actin, desmin, and HMB-45 negative. CD34 stai ned intralesional fibroblasts. Antibody to epithelial membrane antigen stai ned only the perineurium around the tumor masses, suggesting that the tumor s arose inside the nerve sheath. No signs of neurosecretory granules were p resent at ultrastructural level. None of the lesions recurred and none meta stasized over a mean follow-up of 8.1 years.