Case report: Fibromatosis colli in a neonate

Abstract Fibromatosis colli or pseudotumor of infancy of the sternocleidomastoid muscle is a rare cause of a benign neck mass in neonates and infants. If diagnosed correctly, it can be managed conservatively, and unnecessary investigations can be avoided.


Introduction
Fibromatosis colli is a condition in which there is diff use enlargement of the sternocleidomastoid muscle, usually in infancy. [1] Though the exact etiology is not known, it is most likely due to birth trauma. [2] It is one of the causes of congenital torticollis. Though USG is the imaging modality of choice, cross sectional imaging with CT scan or MRI may sometimes be required to further characterize the disease and to know the extent of involvement. Real time USG shows synchronous motion of the mass with the sternocleidomastoid muscle, thus confi rming the diagnosis. We present a case report where fi bromatosis colli was diagnosed using USG, in an infant.

Case Report
A 3 1/2-week-old neonate was referred to the radiology department for USG of a neck swelling on the left side that had been noticed by the parents 2 weeks ago. The swelling was fi rm to hard in consistency and was not warm to touch. The patient was afebrile. There was restriction of neck movements on the aff ected side. The parents reported that the child had had a forceps delivery.
USG showed a thickened sternocleidomastoid muscle on the left ; it had a fusiform appearance and heterogenous echotexture. The fi brillar structure of the muscle fi bers was however maintained [ Figure 1]. In comparison, the right sternocleidomastoid muscle appeared normal [ Figure 2]. There was no cervical lymphadenopathy.
Based on these USG features and the clinical fi ndings, a diagnosis of fi bromatosis colli or pseudotumor of the sternocleidomastoid muscle was considered.
Physiotherapy was started and the swelling showed a slight decrease in size aft er 3 weeks, with the neck movements returning to near normal.

Discussion
It typically presents with a neck swelling at 2-4 weeks of birth, most commonly following a diffi cult delivery (vacuum extraction or forceps delivery). The diagnosis can be made on USG, which shows spindle-shaped thickening of the sternocleidomastoid muscle on the aff ected side in contrast to the normal contralateral side. There is no cervical lymphadenopathy and no vascular invasion or bony involvement as may be seen with other neck masses. Torticollis can develop in around 20% of cases. [3] Bilateral sternocleidomastoid tumors of infancy, though extremely rare, have also been described. [4] Treatment is symptomatic, with physiotherapy and neck stretching exercises. The swelling regresses over a period of time, with complete disappearance by 4-6 months. The diff erential diagnosis of solid tumors in this situation includes rhabdomyosarcoma and neuroblastoma in which, in addition to a neck mass, there can be enlarged cervical lymph nodes, vascular encasement, or invasion of surrounding structures. compared to gradient-recalled T1W images, because of the presence of fi brous tissue. [5] The extent of involved muscle is bett er delineated with MRI than with USG. The cytologic features include bland-appearing fi broblasts and atrophic skeletal muscle, along with muscle giant cells and bare nuclei. [6] To conclude, fi bromatosis colli is a relatively rare cause of neck swelling in neonates and infants and the radiologist must be aware of its imaging features in order to diff erentiate it from other neck masses.