Case Number : Case 1709 - 15 December - Dr Arti Bakshi Posted By: Guest

A very spotty Spot Diagnosis Case for you today from Dr Arti Bakshi.

Cheers, Geoff Cross - DermpathPRO Projects

?cellular neurothekeoma

Same thought: cellular neurothekoma

Same thought. Cellular Neurothekeoma. 

I find this case very interesting, because of mixed neurothekeomatous, micro-nodular arrangement on the left of the lesion, and multi macro-lobular, nerve sheath myxoma-like arrangement on the right. The cellular population is epithelioid and typical of cellular neurothekeoma. I have thought of many differential diagnosis, but cellular neurothekeoma is the more reasonable for me...

Agree with cellular neurothekoma

Neurothekeoma. S100 negative, NKI/C3 positive.

Very interesting! This tumor is much more myxoid than a cellular neurothekeoma is expected to be, and much more cellular than a myxoid neurothekeoma is expected to be.

Unless immunophenotype proves otherwise, I’d call it dermal nerve sheath myxoma (aka myxoid neurothekeoma), since lesion is well-circumscribed with multilobulated growth pattern demarcated by fibrous septa. The nested growth pattern of cellular neurothekeoma is only focal.

Bearing in mind that dermal nerve sheath myxoma and cellular neurothekeoma are now considered unrelated tumors, maybe images above show a collision tumor.

Some very good points highlighted by Robledo and Vicenzo! I called this a cellular neurothekeoma due to the presence of typical (albeit focal) nested epithelioid pattern in conjunction with the immuno panel, which showed that the tumour was diffusely positive for NK1C3 and entirely negative for S100. (so although there is morphological variation within the tumour, it is uniform immunohistochemically).

The spectrum of cellular neurothekeoma has widened and includes cases with prominent myxoid areas . Some such cases have been reported as myxoid cellular neurothekeoma in literature, adding to the confusion with myxoid neurothekeomas, which are unrelated tumours and better labelled a nerve sheath myxomas.

 As per this series of cellular neurothekeoma,  http://www.nature.com/modpathol/journal/v27/n5/full/modpathol2013190a.html, 5/37 cases had prominent myxoid stroma. The authors emphasise that the presence of nests of epithelioid tumour cells with characteristic cytological features, no matter how focal, is the clue to the diagnosis of cellular neurothekeoma. Ofcourse the IHC is mandatory in the distinction in such cases.