Fibromatosis colli (FMC), also termed sternocleidomastoid tumor of infancy, pseudotumor of infancy, and infancy sternocleidomastoid pseudotumor, is an uncommon (incidence: 0.4%-1.3% of live births), congenital tumor in one of the two sternocleidomastoid neck muscles although rare cases have presented with a FMC tumor in both sternocleidomastoid muscles. A tumor is here defined as a growth of tissue that is not coordinated with the normal surrounding tissue and persists in growing even if the original trigger for its growth is removed. FMC tumors are benign growths that may cause disfigurements but are not cancers and do not metastasize (i.e. spread) to distant tissues.As judged by microscopic cytology analyses, fibromatosis colli tumors consist of spindle-shaped fibroblasts (i.e. the most common cell type in connective tissue) located in a background of collagen fibers, decomposing skeletal muscle fibers, and, in some cases, regenerating skeletal muscle fibers. The fibroblasts have a completely normal appearance with no evidence suggesting that they are malignant. The World Health Organization, 2020, classified fibromatosis colli as in the category of benign fibroblastic and myofibroblastic tumors.In the majority of cases, FMC tumors decrease in size and completely resolve by the newborns second year. If left untreated, however, a significant percentage of cases progress to, and are the most frequent cause of, congenital muscular torticollis, i.e. an abnormal, asymmetrical head or neck position commonly called wry neck. Untreated FMC tumors may also progress to facial asymmetry, plagiocephaly (i.e. flattened head), permanent loss of neck mobility, scoliosis (i.e.
If the findings still remain unclear, microscopic examination of fine needle asperates taken from the tumor will, when combined with the imaging findings, the lesion’s natural history, and its clinical presentation, likely confirm the diagnosis of FMC in virtually all cases. Treatment and prognosis
Prompt diagnosis and treatment of FMS is crucial for avoiding the impairments that may follow long-term mal-positioning of infants head such as permanent facial asymmetry, flattened head, loss of neck mobility, and scoliosis. About 95% of infants with minimal limitations in their heads mobility show improvements in this mobility after 4 weeks of an active home stimulation program (i.e. observation, massage, and active and passive stretching) while ~91% of infants with more severe movement limitations show good results after 3 sessions of targeted physiotherapy over a 3–4 month period. The recommended treatment for infants who show no improvements in mobility after 1 year of physical therapy or who initially present at >12 months of age is surgical tenotomy (i.e. cutting) of one of the tendons on the involved sternocleidomastoid muscle. Tenotomy may use the open surgical (i.e. cutting of skin) approach or endoscopic (i.e. percutaneous) approach. The overall prognosis of FMS tumors is good using these treatment measures.Infants presenting with FMS should be examined for the presence of hip dysplasia. See also
Skin lesion


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