Case Number : Case 1468 -09 February Posted By: Guest

Cords and fascicles of spindle shaped cells forming storiform pattern, collagen trapping, involvement of subcutis, pleomorphism but no mitotic figures.,

? Eruptive Dermatofibroma, the present nodule showing histopathological features suggestive of cellular Dermatofibroma

This is indeed a challenging case, when i saw the first picture my first thought was cellular dermatofibroma. But after continuing with the images I was less sure of this idea. I see a dermal proliferation with irregular borders  disposed mainly in fascicles of different size and orientation, cytologically the cells seem to have diffuse atypia with irregular nuclear membranes, small nucleoli and inconspicuous cell borders; some of the cells are clearly fusiform with blunted nuclear borders others are not. I dont perceive mitotic figures. Of particular interest is the adipose tissue seen on picture 5, the presence of adypocites interspersed with a fusiform proliferation would normally make me think of a primary adipocytic neoplasm but I am really not convinced here. Finally the clinical setting makes me also consider a primary cutaneous smooth muscle neoplasm. So, to sum up, I would perform a wide panel of immunos (ck, s100, desmin, smooth muscle actin, caldesmon, factor XIII, ki67) I am not sure but I think this is a smooth muscle neoplasm in the range of leyomioma/aytipical intradermal smooth muscle neoplasm (as proposed by Fletcher) 

What about Cellular Neurothekeoma, fasciculate pattern?

Thinking of an eruptive cellular dermatofibroma. These have been described in a setting of connective tissue disease. The entrapment of fat is very DFSP like. Like Raul has suggested, we require a range of IHC markers. Definitely challenging!

Pseudomyogenic hemangioendothelioma?

Wow! difficult case. I also thought this was eruptive DF