Case Number : Case 909 - 12th December Posted By: Guest

Despite the general resemblance to a dermatofibroma the perivascular concentration of spinde cells and the muliplicity of lesions ar more in keeping with Kaposi's sarcoma.

Kaposi's sarcoma, plaque stage.

I agree, KS.
The most difficult feature of this case, in my opinion, is the lack of red blood cells and plasma cells, I can not see them, but there´s no other vascular differential diagnosis for this case (neither angiosarcoma nor the different kinds of hemangioendotheliomas).

A very early patch stage of Kaposi sarcoma. Without extravasated erythrocytes and fascicles of spindle cells, it´s hard to rule out definitely an inflammatory skin disease, like morphea. Nevertheless, jagged vascular spaces dissecting collagen bundles and a putative promontory sign on picture #2 make me favor Kaposi sarcoma.

Kaposi's sarcoma.

KS

Interesting case. Agree that Kaposi's patch stage is most likely diagnosis, vs. hobnail hemangioma, based on these images.

Despite the bland cytology, there is sparse mitotic activity [lowest left image], increased cellularity, and promontory sign with indisputable single endothelial layers (lacking supporting pericytes) closely applied to surfaces of collagen bundles, and connection to pre-existent vessels. There may be plasma cells in lowest left image. A confirmatory positive stain for HHV8 (and/or clinical correlation) would be of utility.
Differential diagnosis would include:
1. microvenular hemangioma (which had been my first-glance consideration, given classic clinical presentation on arm of a young adult male). However, these lesions are usually solitary, should have easily visible pericytes associated with the dissecting vascular spaces, and show absence of mitotic activity. They often infiltrate arrector pilae, which appears to not be the case in these images. SmActin stain would help highlight the pericytes for equivocal cases.
2. Hobnail hemangioma. (another classic clinical presentation on arm of a young adult male). These are rarely multiple. They can have dissecting architecture with bland endothelial cells deeper in the dermis, and more classic papillary telangiectatic vessels superficially, which may be argued as present in the top two images. Also may have sparse inflammatory infiltrate with plasma cells.

Kaposi's sarcoma. HHV-8 was positive.