A 30-year old male with the tumor of the anterior femoral region that previously has arised for several months.  
The tumor was surgically removed.  
Gross examination revealed a multinodular, grayish-white tumor that measured 5.5x4.5 mm. The lesion was ulcarated, poorly circumscribed.  
Microscopically, the tumor was located in both papillary and reticular dermis as well as in subcutis. The lesion was predominantly composed of spindle cells, pleoimorphic, some of them with multinuclear appearance. Some of tumor cells also had a 'dendritic' processes. Tumor cells were located between preserved lymphatic tissue that was composed of primary and secondary lymphatic follicules. Within the germ centers, we noticed the same cells as in the tumor. Both were positive on CD68. The tumor cells were also positive on S100 and Vimentin but was negative on HMB-45, CD1a and CD21.  
What is your diagnosis? Please, give your comments.

kurt 2006-10-12 18:38	Dear Semir Vranic     instead of uploading the pdf document again, iPath allows you to simply create a link to your original case. If you are in the "histopathology forum", you should be able to click on "refer" button and then you can create a referral in the hematology group.     Alternatively you can also add a "link". click on add button and then in the topmost line on "object type" link. Then you can search your original case or enter it's case number. (this is what I did now).     For the others link is much nicer because they can zoom the images to their preference and work like with any case in iPath.
semir 2006-10-12 20:05	Dear Kurt,     Thank you very much for your assistance. I will remove the PDF file, just leaving the link to the originally posted file.
hurwitz 2006-10-17 18:04	I do not know how to call this lesion, but my impression is that this is rather a reactive process containing interdigitatig reticulim cells (S-100+) and hstiocytes (CD68+). Would you mind to do a PAS stain, perhaps this will help to detect some microroganisms?   I will also ask others for comments.
semir 2006-10-17 22:20	No, we did not perform a PAS staining but will do that as soon as possible. Will also stain for other pathogens (e.g. TB). The case is also sent for second opinion since it looks very unusual.
FFalko 2006-10-18 11:25	Dear Semir Vranic,     it is hard to tell for me the nature of the lesion from the images provided. According to your gross description, it seems to be neoplastic rather than inflammatory, although the histology does not convincingly exclude the latter possibility. If neoplastic, a dermal tumor of the "fibrohistiocytic" lineage (DFSP etc.) and a tumor of accessory cells are in the differential. A CD34 stain is certainly required for DSFP. I am not sure whether CD68 and S100 mark the same cell populations, the S100 stain marks only occasional cells with dendritic processes. THe (rare) cases of tumor of interdigitating reticulum cells I have seen showed bundles of spindle cells with strong and homgoeneous S100 and CD68 staining, unlike the variegated pattern in this case. Certainly an interesting and difficult case!
kunze 2006-10-18 12:45	It's indeed an interesting and challenging case. Additional stains (CD34, CD31, FVIII, PAS, AFB) are necessary as recommended by the colleagues. Though we have no typical Touton cells the histological features remember to a juvenile xanthogranuloma and this entity should enter the dd. along with fibrohistiocytic skin tumors and inflammatory granulomas.
ugnius 2006-10-18 12:58	One may say, that additional scanning and conventional photos would be of value. The intensive lymphoid infiltrate in no1 sometimes is not a part of lymph node?   An opposite idea may be inflammatory myofibroblastic tumor (ALK1?).
semir 2006-10-18 19:30	Thanks for all your comments. I appreciate them.   In the meantime, I captured the gross appearance of the tumor again and put it here. It really looks like a malignant tumor.   We performed CD34 staining but CD34 was negative. ALK1 analysis was not done because of too many mitotic figures in order to render the diagnosis of inflammatory myofibroblastic tumor.
ugnius 2006-10-18 20:32	What about cytokeratins? Some clear cells show perinuclear eosinophilic inclussions (RCC mts)?   Really more pictures would be of value. With mitotic activity too:)
nurija 2006-10-25 19:41	My impression is that this is Rosai Dorfam diseae without involment of lymph node
nurija 2006-11-06 20:01	Official report from Emina Emilia Torlakovic, MDPhD, Department of Pathology, Royal University Hospital,Saskatoon   Diagnosis:   Most compatible with cutaneous Rosai-Dorfman disease, see comment.     Comment:   This is a rare entity and the morphologic appearance in the skin is somewhat different than that in the lymph nodes. The differential diagnosis in this particular biopsy includes other S-100 dendritic cell disorders, in the first place interdigitating dendritic cell sarcoma. However, the latter diangosis is very unlikely based on morphologic appearance and cellular composition of the lesion in this skin biopsy.   Clinical correlation is necessary and conservative treatment for Rosai-Dorfman disease is indicated to start with. Close clinical follow up is indicated and re-biopsy may be considered is progression of the disease is noted.
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