I cannot comment much on the cystic change, but am worried about the intravascular infiltrate. Uniform clusters of atypical cells are distending the vascular spaces. This finding may be related, but may also be unrelated to the cystic lesion of the skin. I do not see many skin biopsies. Nevertheless, I cannot recall seeing any benign lesion that forms such atypical intravascular clusters. Intravascular lymphomas are extremely difficult to diagnose and many are diagnosed on the post mortem examination. Most of these are readily B-cell lesions, but rare T-cell lesions have been described. Last year I have seen one case of "intravascular" ALCL (you may also try to do ALK). Therefore, I would recommend further clinical (other lesions, systemic symptoms, headache, other) and pathological (other T-cell markers and PCR) evaluation to rule out such a possibility.

Thank you. ALK1(-), but selected cell clusters are gone in sections...

The suggestion of intravascular lymphoma is excellent.The only thing I would like to add is that BMB is an excellent tool for in vivo diagnosis of intravascular lymphoma.

The infiltrates can also be reactive due to the inflamamtory process and ulceration of the cyst. There is a mixed population of lymphoid cells with some B-cells, some T-cells and some macrophages. Did you stain for Ki67?

I agree with the comments the atypical cells, and the only way to resolve the diagnosis may be re-biopsy. However, I am also concerned about the epithelial lesion, which does not look like a simple epidermal inclusion cyst to me. It has a crater shape and prominent epithelial cell proliferation, suggestive of a keratoacanthoma or other proliferative lesion. Have dermatopathologists looked at it?

Yes Diane, a keratoacanthoma is a possibility, but what can we do with the atypical intravascular lymphoid cells ???

We have to take the whole story into consideration, the patients has a skin lesion which is highly inflammed and ulcerated. Activated T-cells can look quite peculiar. Any clinical follow-up?

I think that this is a CD4+/CD30+ intravascular anaplastic T-cell lymphoma in association with keratoacanthoma. This has been reported twice to my knowledge: (1) Cespedes YP, Rockley PF, Flores F, et al. Is there a special relationship between CD30-positive lymphoproliferative disorders and epidermal proliferation? J Cutan Pathol 2000;27:271-5; and (2) Tronnier M, Merz H. Anaplastic large cell lymphoma and keratoacanthoma. Hautarzt 2004;55:182-5. A very interesting case, possibly worth a case report.

Thank you for comments. An idea about "resolving" keratoacanthoma was evolved too. It's not clear are these changes sufficient for ALCL (T) diagnosis. The COMMENT in the report was appended, but the material was sent from regional hospital so follow up is not assured. I will inform you if get any further info about the case. The cell group is too small and disapearing in sections to prove TCR monoclonality.

On reflection, I think I may have been a little too hasty in my diagnosis. It could be that the lymphoid infiltrate would qualify for lymphomatoid papulosis; I don't have much experience with this entity. And keratoacanthomas are not usually cystic. However, it would still be useful to compare this case with cases described in the literature; they sound very much alike. Possibly there is a way to assess T-cell production of an epithelial growth factor, if the lesion is re-biopsed. I would suggest complete excision, if not already done, with clear surgical margins if possible.

Histology shows a infundibular hairfollicle cyst with perifollicular chronic inflammation and foreign body reaction. The atypical intravascular cells might be activated T cells, if differential blood count has ruled out lymphoma and staining for PAS, Leder, or lysozyme has ruled out secondary skin infiltate of myeloic leukemia or myelodysplastic syndrome.