Microscopic histopathological analyses of appropriately dye-stained<unk>  tissues typically show a non-encapsulated small tumor composed of bundles of uniform spindle-shaped cells that combine physical features of fibroblasts (the most common cell type in connective tissue) with those of myofibroblasts (contractile, spindle-shaped cells that are identifiable by their expression of α-smooth muscle actin) in a background of collagen fibers. In hematoxylin and eosin-stained tissues, the spindle-shaped cells have pale eosinophilic (i.e. red or pink due to uptake of eosin) cytoplasm with plump and elongated nuclei composed of granulated (i.e. having many small, distinct parts) chromatin. The most pathognomonic (i.e. indicative of a particular disease) feature of these cells is the presence of cytoplasmic perinuclear inclusion bodies which usually are small, round, pale pink bodies on hematoxylin and eosin staining that often indent their parent cells' nuclei. These inclusions are composed of densely packed vimentin and actin filaments. Newer tumors show relatively abundant inclusion bodies and scarce collagen fibers while older tumors show few or no detectable inclusion bodies and abundant collagen fibers. Immunohistochemical analyses show that the spindle-shaped cells typically express α-smooth muscle actin, calponin, desmin, and CD99 proteins but not S100 protein or glial fibrillary acidic protein.
Infantile digital fibromatosis
Plantar fibromatosis
Juvenile plantar dermatosis
Superficial acral fibromyxoma
Aggressive infantile fibromatosis
Juvenile hyaline fibromatosis
Subungual exostosis
Diffuse infantile fibromatosis