Neurothekeoma (NTK) is a neoplasm of uncertain lineage. Previous descriptions classified NTK as cellular (immature) and myxoid (mature; classical) types based on the degree of cellularity. Currently, however, it is suggested that some highly myxoid and the previously described transitional or mixed variants with evidence of schwannian differentiation are better classified as dermal nerve sheath myxoma (see Chap. 4). NTK as currently classified on the other hand shows no convincing evidence of peripheral nerve lineage, and comprises a spectrum of tumors with variable degrees of cellularity and myxoid change. While the precise histogenesis is uncertain, some authors suggest this tumor may be of smooth muscle or fibrohistiocytic lineage. In general NTK is a benign neoplasm. While atypical forms exist, a true malignant variant has not yet been established.
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