Answer: Kaposi’s sarcoma

Histology: A large nodule both in the superficial and deep dermis is present without involvement of the overlying epidermis. Even at low magnification, the lesion shows a hemorrhagic component. At higher magnification, the spindle cells lack significant pleomorphism although scattered mitotic activity is evident. Intercalated between the spindle cells are red blood cells, which in areas has the appearance of cords of cells situated within slit-like spaces. The surrounding connective tissue contains hemosiderin deposition. These findings are classic for Kaposi’s sarcoma.

Discussion: Angiosarcoma rarely has a prominent spindle cell pattern. Rather, epithelioid appearing cells line better developed interanastomosing vascular channels. Nodular fasciitis is a spindle cell proliferation, which also reveals extravasated red blood cells. Nodular fasciitis is a deeper seated lesion, and would not be found in the superficial dermis. Furthermore, nodular fasciitis in its early more cellular phase has a looser arrangement of cells in a more myxoid background. The cells in nodular fasciitis resemble tissue culture-like fibroblasts with uniformly enlarged nuclei containing prominent nucleoli. In less myxoid older lesions of nodular fasciitis, the lesion is much more fibrous. Malignant melanoma may have a prominent spindle cell component, although there is usually some epidermal involvement. Often the spindle cells have more cytologic atypia consisting of large nuclei containing eosinophilic prominent nucleoli. In this case, the presence of extravasated red blood cells and red blood cells in slit-like channels between spindle cells are pathognomic for Kaposi’s sarcoma.