Case Number : Case 1795 - 14 April - Dr Richard A Carr Posted By: Guest

Good Friday just got better, here is a lovely case from Dr RIchard A Carr to get the Easter weekend off to a good start.

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ossifying dermatofibroma

Osteoma cutis??

Another tricking case...

It's a digital periungueal tumor, I guess, and the DDs turn around 3 ossifying lesions: subungueal exostosis, osteoma cutis, fibroosseous pseudotumor of the digits.

The first should contain some cartilaginous outer sheath...

The second should show only mature bone trabeculae.

The Fibroosseous Pseudotumor of the digits contains fasciitis-like activated fibroblasts, osteoblastic rimmed osteoid, pseudozonation resembling myositis ossificans, and in this case there is much mature trabecular bone...advanced growth stage? CPC is advisable in this case!

My spot is : Fibroosseous Pseudotumor of the digits.

Agree Vincenzo I also think this is periungueal. This is a reactive process with many myofibroblasts (For the new members, their basophilic cytoplasm, prominent nucleoli and stellate shape are characteristic) that we can see on picture 7 and ossification. We can also appreciate edematous and non- edematous zones at the periphery resembling the aspect seen in some fasciitis. If the clinical impression fits (localization, history of trauma/working trauma on the zone etc.) this is fibro-osseous pseudotumor of the digits, that is just a fancy name of a mere reactive myofibroblastic process.

I actually thought of subungual exostosis, but after verifying, I agree with Vincenzo that the lack of outer cartilaginous cap makes fibro-osseus pseudotumor of the digit better choice.

Thanks Vincenzo, Raul and Mona. I called this a subungual exostosis in my original report but agree your arguments (i.e. lack of cartilaginous cap) support a diagnosis of fibro-osseus pseudotumour.

I was not really happy with the diagnosis of fibro-osseus pseudotumour in this case so asked a nationally reputed soft tissue/bone pathologist to comment (they would rather remain nameless), correspondence as follows:

Dr Carr: "Dear X, I posted this case on Dermpathpro and it had caused some confusion - not least for me!"

Dr X: "It is clearly a benign ossifying mass by virtue of its mature compact bone production. The orientation looks ood to me - is it exophytic? If so, why no epithelial or ulcer slugh covering it? It may be cross-cut. Subungual exostosis do not have to have a cartilage cap. To do this properly any pre-op X-ray (which may not have been done) needs to be checked to see if there is a bone or periosteal attachment.  Certainly the subungual site favours and "exostosis" and the appearance is not inconsistent."

Dr Carr: "Forgot to say I think the nail plate was evulsed first. We can just see the nail bed epithelium on the surface - not frankly ulcerated as far as I can see from the images I took"

Dr X: "Yes, I thought that there was nail bed present. It's still a little odd looking, being so exophytic. The X-ray could help as exostoses are periosteal in origin, not actually arising from the bone (no continuity with bone)."