Benign cutaneous biphasic hybrid tumor of perineurioma and cellular neurothekeoma: A case report expanding the clinical and histopathologic features of a recently described entity.

Benign cutaneous plexiform hybrid tumor of perineurioma and cellular neurothekeoma (BCPHTPCN) is a recently described entity that presents as a solitary papule in the perioral area. As implied by its name, BCPHTPCN displays microscopic features of both perineurioma and cellular neurothekeoma arranged in a plexiform pattern. We report a case of nonplexiform benign cutaneous biphasic hybrid tumor of perineurioma and cellular neurothekeoma in a 36-year-old woman, who presented with a 4-year history of a firm, flesh-colored left ankle nodule. Histologically, there was a biphasic, well-circumscribed unencapsulated dermal mesenchymal proliferation with no connection to the epidermis, which exhibited mild acanthosis with slightly pigmented basal keratinocytes and overlying parakeratosis. The proliferation consisted of uniform bland spindle cells with bipolar cytoplasmic processes arranged in whorls with interspersed islands of epithelioid cells. Immunohistochemically, the spindle cell component was positive for CD34, EMA, and GLUT-1, consistent with perineurial differentiation, whereas the epithelioid nests were positive for NKI/C3 and MiTF, as expected in neurothekeoma. Stains for S100 protein, SOX10, desmin, claudin, pan-melanoma markers, and NSE were negative. We believe this case expands the histopathologic spectrum of BCPHTPCN showing that it can be grown in a nonplexiform pattern, and we suggest the term benign cutaneous biphasic hybrid tumor of perineurioma and cellular neurothekeoma as a more precise name. It is also, to the best of our knowledge, the first case reported outside the head and neck area.

SOX-10 and MiTF expression in cellular and 'mixed' neurothekeoma.

BACKGROUND: Neurothekeoma and nerve sheath myxoma have long been interpreted as related tumors that share nerve sheath linage. Lack of S100 expression in neurothekeoma and similarities of gene expression profiles between neurothekeoma and fibrohistiocytic tumors have created reasonable doubt about this concept. SOX-10 represents a marker for schwannian and melanocytic differentiation, and is expressed in other tumors of nerve sheath linage. Microphthalmia transcription factor (MiTF) expression has been repeatedly reported in cellular neurothekeoma in the recent literature and was proposed as a helpful marker in this entity. METHODS: We investigated 25 cases of cellular neurothekeoma, 8 cases of mixed neurothekeoma and 1 case of nerve sheath myxoma for the expression of SOX-10, MiTF, S100, NKI/C3, Melan-A and smooth muscle actin (SMA) using immunohistochemistry. RESULTS: A lack of SOX-10 expression was demonstrated in 100% of cellular and mixed neurothekeomas, but was present in the case of nerve sheath myxoma. More than two thirds of neurothekeomas showed very focal or no reactivity with MiTF. CONCLUSIONS: Our data suggest that neurothekeoma and nerve sheath myxoma are unrelated, and that cellular and mixed neurothekeoma may not be of nerve sheath lineage. In addition, MiTF should not be regarded as a useful marker in neurothekeoma.

Classic neurothekeoma (nerve sheath myxoma) and cellular neurothekeoma of the oral mucosa: immunohistochemical profiles.

BACKGROUND: Classic neurothekeoma (nerve sheath myxoma) is regarded as being a true benign cutaneous tumor of nerve sheath origin. Cellular neurothekeoma was separated from the classic type by histogenesis, morphology and immunophenotype. Whether cellular neurothekeoma represents a continuum within the spectrum of classic neurothekeoma or is an independent entity is controversial. Only a small number of classic neurothekeomas of the oral mucosa have been reported and there are even fewer publications on cellular neurothekeoma. We analyzed a series of oral neurothekeomas (classic and cellular) with a panel of neural and other mesenchymal markers to enhance their diagnosis and classification. METHODS: One cellular and three classic neurothekeomas were submitted to a panel of immunohistochemical stains with antibodies against S100, S100A6, NSE, NKI/C3, PGP9.5, α-SMA, HHF-35, CD68 and vimentin. Two cases of neurofibroma (plexiform type), representing a true lesion of neural origin, served as control. RESULTS: The cellular neurothekeoma yielded a positive immunoreaction for S100A6 and NKI/C3 and a negative immunoreaction for S-100. The classic neurothekeomas demonstrated a positive reaction for S-100 and S100A6, but a negative one for NKI/C3. Other markers were non-contributory to distinguishing between these types of lesions. CONCLUSIONS: The small number of reported oral neurothekeomas (classic and cellular) could be due, in part, to the lack of recognition of their particular morphologic and immunohistochemical features. Our results indicate that testing for NKI/C3 immunoreactivity may be of value in distinguishing between cellular and classic neurothekeoma.

Cellular 'neurothekeoma': an epithelioid variant of dermatofibroma?

AIMS: Cellular neurothekeoma is a rare benign cutaneous neoplasm with conflicting opinions regarding its histogenetic origin (nerve sheath, smooth muscle, myofibroblasts) as well as its relation to myxoid neurothekeoma (nerve sheath myxoma). The present series describes 15 cases whose clinicopathological features indicate a relationship to dermatofibroma. METHODS AND RESULTS: In this retrospective clinicopathological study, the lesions preferentially occurred in adolescents to young adults on the upper half of the body, often clinically diagnosed as some kind of fibrohistiocytic tissue response. Besides characteristic whorled nests to fascicles of palely eosinophilic epithelioid cells, all lesions showed variable clues pointing to dermatofibroma: acanthosis, ill-defined storiform periphery, peripherally accentuated prominent sclerosis and lymphocytic demarcation/infiltration. Immunohistochemically, all cases were positive with NK1C3 (CD57), KiM1p and proliferating cell nuclear antigen, seven were positive for neurone specific enolase, five for factor XIIIa, six for smooth muscle specific actin and three for E9, an antimetallothionein marker. These findings are similar to those of conventional dermatofibromas, the variability of the profile being best explained by time cycle and function dependent changes. Ultrastructurally, two cases showed microfilaments, attachment plaques, prominent pinocytosis and focal remnants of basal lamina. A careful study of the data and photomicrographs from the literature reveals that in many cases similar conclusions could be reached. Obvious discrepancies are most likely due to the confusion with myxoid neurothekeoma, a well circumscribed, more spindly and myxoid, S100 positive lesion of Schwannian origin. CONCLUSION: The appearance of dermatofibromas is markedly influenced by architectural, e.g. in deep penetrating dermatofibroma, and/or cellular/stromal criteria, e.g. in epithelioid cell histiocytoma or sclerosing dermatofibroma. Cellular neurothekeoma seems to be a variant of dermatofibromas with both architectural and cellular/stromal peculiarities, i.e. plexiform pattern, epithelioid cytology and stromal sclerosis.

[Cellular "neurothekeoma": an epithelioid variant of dermatofibroma?]. / Zelluläres "Neurothekeom": Eine epithelioide Variante eines Dermatofibroms?

AIMS: The present series describes 15 cellular neurothekeomas whose clinicopathologic features indicate a close relationship to dermatofibroma. METHODS: Retrospective clinicopathologic study. RESULTS: Lesions preferentially occurred in adolescents to young adults on the upper half of the body, often clinically diagnosed as some kind of fibrohistiocytic tissue response. Besides characteristic whorled nests to fascicles of palely eosinophilic epithelioid cells all lesions showed variable clues pointing to dermatofibroma: acanthosis, ill-defined storiform periphery, peripherally accentuated prominent sclerosis and lymphocytic demarcation/infiltration. All cases were positive with NK1C3 (CD 57), Ki-M1p and proliferating cell nuclear antigen, 7 for neuron specific enolase, 5 for factor XIIIa, 6 for smooth muscle actin and 3 with E9, an anti-metallothionein marker. These findings are similar to other types of dermatofibromas, the variability of the profile being best explained by time cycle and function dependent changes. Ultrastructurally, two cases showed microfilaments, attachment plaques, prominent pinocytosis and focal remnants of basal lamina. A careful study of data and microphotographs from the literature reveals that in many cases similar conclusions can be reached. Obvious discrepancies are most likely due to the confusion with myxoid neurothekeoma, a well circumscribed, more spindly and myxoid, S 100 positive lesion of Schwannian origin. CONCLUSION: According to our results cellular neurothekeoma seems to be a whorled-nested to plexiform epithelioid variant of dermatofibroma.

[Cutaneous neural neoplasms--an update]. / Kutane Tumoren des Nervenhüllgewebes--eine Ubersicht.

Until recently, benign cutaneous neural tumours which do not fulfill criteria for either neurofibroma or schwannoma often were lumped into the broad category of benign peripheral nerve sheath tumours (PNST). However, during the last years a number of new entities of neural tumours has been described, and advances in immunohistochemistry and electronmicroscopy have helped us better to understand the cytological differentiation in these neoplasms. The knowledge of these distinctive neoplasms is necessary in order to avoid diagnostic pitfalls and misdiagnosis of more aggressive neoplasms. These distinctive lesions include: Neurothekeoma, which can be divided into classical myxoid and cellular types showing characteristic histological and immunohistochemical features. Typical neurothekeoma (nerve sheath myxoma) is a lobular or nodular dermal neoplasm composed of plump spindled or stellated S-100 positive tumour cells set in a myxoid stroma. In contrast cellular neurothekeoma is characterized as an ill-defined dermal neoplasm composed of concentric nests and fascicles of spindle-shaped and epitheloid tumour cells, which are S-100 negative but stain positively for NKIC3. The evidence of intermediate forms of neurothekeoma showing features of ordinary, hypocellular neurothekeoma and cellular neurothekeoma, as well as ultrastructural studies emphasize, that both variants represent a spectrum of neurothekeoma. Solitary circumscribed neuroma ("palisaded encapsulated neuroma") manifests mainly as a skin-colored or pink papule or nodule, and is most often located on the face. Histologically, solitary circumscribed neuroma is a well-circumscribed round or ovoid dermal neoplasm composed of interwoven fascicles of schwann cells, which stain positively for S-100 protein, and numerous neurofilament positive axons surrounded partly by fibroblasts and EMA-positive perineurial cells. Perineurioma is a rare well-circumscribed neoplasm which occurs mainly in subcutaneous tissue and only rarely in the dermis and in deep soft tissue. Perineurioma is composed of elongated bipolar spindle-shaped tumour cells which are arranged in a storiform, linear or lamellated growth pattern. The tumour cells stain positively for vimentin and EMA, and for CD34 in a number of cases, but lack positivity for S-100 protein, neurofilament and desmoplakin. In addition unusual forms of schwannoma including cellular schwannoma, solitary plexiform schwannoma, and melanocytic schwannoma are briefly discussed.