Case Number : Case 1988 - 18 Jan 2018 Posted By: Patrick Shenjere

Plexiform lesion. Plexiform fibrohistiocytic tumor?

Cellular neurothekeoma or plexiform fibrohistiocytic tumor. 

Do not know how to reliably distinguish these two entities.

Agree with plexiform fibrohistiocytic tumor. Young age and a few multinucleated cells.

Agree with plexiform fibrohistiocytic tumor. Would do MiTF immunostaining, though (-ve in plexiform fibrohistiocytic tumor, positive in cellular neurothekeoma).

Plexiform fibrohistiocytic tumor

Agree with PFHT!

Beautiful

Dear All 

Dr Shenjere's final diagnosis was: Cellular neurothekeoma with atypia (atypical cellular neurothekeoma)

Differentials he considered are: Melanoma; Atypical Spitz naevus/Spitz tumour of uncertain malignant potential; Myxofibrosarcoma; Epithelioid sarcoma

From Dr Shenjere:

The main differential diagnosis in this case is between a plexiform fibrohistiocytic tumour and a cellular neurothekeoma. These entities have significant histologic overlap, and in rare cases one is unable to make a confident distinction between them, leading some authors to suggest that they may be the same entity or parts of a spectrum of lesions . The morphological involvement of the upper dermis and presence of nuclear variability, with some areas showing significant pleomorphism and atypical mitoses – not apparent in the pictures provided) seen in this case are more in keeping with a cellular neurothekeoma with atypia(atypical cellular neurothekeoma). The tumour is positive for MiTF. The other differentials one might consider include melanoma; Atypical Spitz naevus/Spitz tumour of uncertain malignant potential; Myxofibrosarcoma; Epithelioid sarcoma, depending on the cellular morphology and degree of nuclear pleomorphism.