Solitary subcutaneous mucinosis surrounded by bizarre-shaped, factor XIIIa-positive cells with intranuclear vacuoles

We describe a subcutaneous mucinosis developing in the right cheek of a 38-year-old man. Histologic examination revealed bipolar fibroblast-like cells embedded in a well demarcated mucinous stroma in the subcutis without a manifest reticulin network. In addition, bizarre, sometimes multinucleate, cells with intranuclear vacuoles were found at the periphery of the mucinous stroma. Immunohistologically, both the bipolar fibroblastic cells and bizarre-shaped cells were positive for vimentin, but were negative for smooth muscle A-actin, desmin, CD34, S-100, trypsin, or chymotrypsin. However, the latter reacted to anti-factor XIIIa antibody, sugggesting that they are derived from dermal dendritic cells. We think that this solitary subcutaneous mucinosis is a unique variant of cutaneous focal mucinosis, because neither a reticulin network nor reactivity to anti-smooth muscle A-actin antibody were demonstrable.