Fibromatosis Colli
Fibromatosis colli is benign focal or fusiform enlargement of the sternocleidomastoid muscle in infants that usually regresses by 6 to 8 months of age.
It is thought to be due to trauma to the sternocleidomastoid muscle or to a positioning abnormality in utero.
Ultrasound of the muscle shows either diffuse enlargement or a focal hyperechoic mass.
MRI shows low signal intensity on T2-weighted images due to fibrosis in the sternocleidomastoid muscle.
