Fibromatosis colli: A rare neck mass of the sternocleidomastoid muscle in an infant: A case report

Fibromatosis colli (FC), also known as sternocleidomastoid pseudotumor of infancy, is a rare benign proliferation of fibrous tissue within the sternocleidomastoid muscle. It typically presents as a unilateral neck mass during the first weeks of life. Although self-limiting, early recognition is essential to prevent unnecessary investigations and to reduce the risk of complications such as congenital torticollis. We report the case of a 3-week-old female neonate who presented with a painless, left-sided neck swelling of one week’s duration. Clinical examination revealed a firm, non-tender mass along the sternocleidomastoid muscle. Ultrasonography confirmed the diagnosis of Fibromatosis colli. The patient was managed conservatively with physiotherapy, resulting in near-complete resolution of the mass and restoration of normal neck mobility within three months. Fibromatosis colli is an uncommon but clinically significant cause of neck swelling in neonates and may closely mimic neoplastic lesions. It should be considered in the differential diagnosis of unilateral neck masses in early infancy. Accurate diagnosis is typically achieved through targeted clinical examination complemented by ultrasonography. Early initiation of physiotherapy is highly effective, typically resulting in complete recovery without the need for surgical intervention. Timely recognition and differentiation from other neonatal neck masses are crucial to avoid unnecessary invasive procedures, alleviate parental anxiety, and prevent complications such as persistent torticollis and craniofacial asymmetry.