| Discussion: |
The differential diagnosis of neck masses in infancy includes infection, congenital cysts, neoplasm, or traumatic lesions. The sternocleidomastoid tumor of infancy, or fibromatosis colli, is a localized fibrous tissue mass within the sternocleidomastoid (SCM) muscle. An ipsilateral head tilt and contralateral chin rotation commonly occur, giving rise to the popular connotation—"torticollis." Fetal intrauterine malposition, birth trauma, or vascular compromise has been proposed as possible etiologies for this benign, self-limited condition. Associated problems may include congenital hip dysplasia, clubfoot, and Erb's palsy.
The lateral neck mass commonly is noted by a parent at 4 to 6 weeks of age and occurs with equal frequency on the right and left sides of the neck. The diagnosis of fibromatosis colli often can be made on the basis of a thorough history and physical exam. However, additional studies may be helpful to confirm the clinician's impression. Ultrasonography is a noninvasive study that is relatively inexpensive and provides highly specific imaging for this condition. This modality can be performed without the need for sedation and avoids exposure to ionizing radiation. In these cases, the ultrasound demonstrates a mass within the mid to lower sternocleidomastoid muscle with an equal frequency of heterogeneous or homogeneous characteristics (Figure 1). Synchronous movement of the mass with the muscle is seen with real time sonography.
The mass of fibromatosis colli disappears by 6 to 8 months of age in 80% of cases. Five to 20% of patients may develop true muscular torticollis.[5,6] Treatment is conservative and includes passive and active range of motion exercises to prevent contracture and permanent shortening of the SCM muscle. Uncorrected rotation and tilting of the head will lead to permanent fibrosis and contraction of the SCM muscle with progressive craniofacial growth asymmetry (nonsynostotic positional plagiocephaly)—hence the urgency for prompt and appropriate intervention. In such cases, surgical release may be necessary.