To the Editor:
We appreciate the interest Dr. Zamecnik has taken in our paper (1). Dr. Zamecnik brings up an interesting point: the presence of adipocytes in a soft tissue perineurioma.
The neurosustentacular system includes Schwann (sheath) cells, endoneurial cells, and perineurial cells. These cells and the melanocytes are neurocristic migrants to the skin. These migrants express either neurosustentacular, melanocytic, or fibrogenic functions depending on their location (2). Some neural crest cells that have already migrated may be committed to distinct lineages and others are multipotent cells (stem cells or self-renewing) (3,4). Moreover, the dermal effector cells are considered a mutable continuum that becomes apparent in the neurocristic neoplasms or dysplasias (abnormal tissue developments) of the skin. The existence of pigmented neurofibromas, melanotic schwannomas, the Bednar tumor (a variant of dermatofibrosarcoma protuberans), and the commonly observed phenomenon of schwannian differentiation, or neurotization, in acquired melanocytic nevi (5) underscore this assertion. Furthermore, Misago et al. (6) described an immature nerve sheath myxoma with some features of neurofibroma and scattered dermal melanocytes. Therefore, the neoplastic or dysplastic effector cell has the capacity to express one, two, or all three options in the skin (2). Thus, the tactoid body, and ovoid cluster of cells resembling Wagner-Meissner corpuscles with some perineural features, can be observed in melanocytic nevi and in neurofibromas. This tactoid body (or nevic corpuscle) is a marker for neuromesenchyme in tumors and dysplasias (2). The neurocristic-differentiated cells of the dermis latently retain the potential of their embryonic relatives and may express mesenchymal properties including lipomatous differentiation (2). Therefore, the capacity of nerve-sheath tumors to exhibit divergent differentiation (7,8), or so-called heterotopic elements, is allowed by its neural crest origin, where the mesenchymal tissue is pluripotent and forms the entire soft tissue and bone of the head. Thus, lipomatous differentiation has been observed in melanocytic nevi (9), schwannoma (10), and neurofibroma (1,11). Zamecnik (12) has proved that perineurioma must be added to the list of neuroectodermal lesions that may contain adipocytes. This finding offers further support for the concept of the origin of mesenchymal tissues from stem cells (or effector cells) of the neural crest.
J. Fernando Val-Bernal, M.D.
M. Francisca Garijo, M.D.
Daniel Val, M.D.
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12. Zamecnik M. Perineurioma with adipocytes (lipomatous perineuroma) [letter]. Am J Dermatopathol 2003: 25;.