Histologically, the epidermis was focally atrophic, and the dermis was increased in thickness, showing a spindle-cell proliferation that extended into the subcutaneous fat and included a reduction of cutaneous adnexa as well as a moderate collagenous component. A mild increase in perivascular mast cells was also noted.
Immunohistochemical findings included CD34 and factor XIIIa immunoreactivity in a majority of spindle cells, suggesting a dermal dendritic cell phenotype of the proliferating population. The immunoreactivity of S100 protein and CD68 was not significant. An orcein stain demonstrated that elastic fibers were diminished.
Atrophic Congenital Lesion on the Back—Diagnosis. Arch Dermatol. 2006;142(7):921-926. doi:10.1001/archderm.142.7.921-g