FMC tumors most commonly present as slow-growing, firm, mobile, nontender, spindle-shaped masses in the lower two-thirds of the sternocleidomastoid muscle of infants within 8 weeks (average: 24 days) of delivery. At diagnosis, these infants' heads may tilt toward the side with the mass while their chins tilt to the opposite, uninvolved side. This tilting is due to sternocleidomastoid muscle contracture. FMC tumors are more common in males and the right sternocleidomastoid muscle although very rare cases present with bilateral tumors. Untreated, the masses may continue to grow for weeks after birth but then stabilize, start regressing after 4-8 months of life, and over the ensuing 1-2 years typically fully resolve. In three studies, >25%, >50% and >80% of these infants have had difficult deliveries such as a breech birth, delivery requiring forceps, primigravida birth (i.e. mothers first child) , prolonged, difficult labor, or delivery by Caesarean section. From 6-20% of newborns with<unk>  also present with other congenital lesions such as hip dysplasia or, less commonly, facial asymmetry. Pathology== Microscopic histopathological analyses of biopsied FMC tumor tissues typically find benign-appearing, spindle-shaped fibroblasts, decomposing skeletal muscle fibers, and, in some cases, regenerating skeletal muscle fibers in a<unk> gen fiber-containing background. If necessary, these tumors are typically diagnosed by microscopic examination of fine-needle aspiration samples rather than the more invasive approach of tumor biopsy sampling. The asperates show scant to moderately cellular, scattered, oval-shaped to spindle-shaped fibroblasts, naked nuclei (i.e. cell nuclei virtually devoid of other cell elements such as the cytoplasm), wisps of<unk> gen, atrophic, degenerating muscle fibers, regenerating muscle fibers, and intact skeletal muscle cells containing multiple nuclei. There is no evidence of inflammation, hemorrhage, cell necrosis, or rapidly dividing and/or proliferating cells.
Fibromatosis colli
Pseudoxanthoma elasticum
Florid cutaneous papillomatosis
Lichen sclerosus
Necrobiosis lipoidica
Keratosis pilaris atrophicans
Keratosis pilaris
Elastosis perforans serpiginosa