Calcifying fibrous pseudotumor involving the neck of a five-week-old infant. Presence of factor XIIIa in the lesional cells.

Calcifying fibrous pseudotumor is an uncommon lesion characterized by hyalinized collagen, psammomatous or dystrophic calcifications, and a predominantly lymphoplasmacytic infiltrate. Although the pathogenesis is unclear, a possible relationship with other inflammatory "pseudotumors" has been proposed. We describe the pathology of two right neck calcifying fibrous pseudotumors present in a five-week-old female infant. The masses had many of the pathologic features of calcifying fibrous pseudotumor. The presence of a florid, mixed infiltrate, and the occurrence of more than one lesion in the same patient, favor the proposal that calcifying fibrous pseudotumor may be a sclerosing end stage of inflammatory myofibroblastic tumor. However, the presence of a previously undescribed participation of Factor XIIIa-positive cells suggests that the tumor may be of dermal dendrocyte origin.