Pseudotumor of sternomastoid muscle

Synonym: This condition is also known as Fibromastosis colli.

Introduction: This is a disorder of infancy. It is a non neoplastic condition involving the sternomastoid muscle. Its exact etiopathology is largely unknown, but prenatal and antinatal events have been implicated.

This condition is characterised by diffuse enlargement of the involved sternomastoid muscle. This enlargement is invariably associated with torticollis. This disorder usually presents as swelling over one side of neck. This swelling usually begins within 4-6 weeks after birth, and is commonly associated with difficult / vacuum / forceps delivery.

The swelling is usually firm to hard in consistency, and is not warm or tender. These patients are usually afebrile and always demonstrate restricted movements over that side of the neck.

Ultrasonogram: Is diagnostic. Real time ultrasonogram shows the mass to be moving along with sternomastoid muscle. This feature is really confirmatory. Eventhough this condition is commonly unilateral, bilateral involvement has also been documented. The swelling is usually spindle shaped.

CT scan: Shows diffuse isodense enlargement of sternomastoid muscle.

MRI scan: T2 weighted images show decreased signal intensity of the mass due to fibrosis. The extent of muscle involvement can be clearly delineated in MRI.

Differential diagnosis:

1. Soft tissue tumors
2. Abscess
3. Lymphadenitis
4. Ectopic thyroid tissue
5. Hemangioma
6. Congenital goitre
7. Dermoid cyst
8. Accessory lobe of thymus

Management:

Physiotherapy when started early is really beneficial. These exercises may range from passive to active aimed at preventing development of permanent contractures and shortening of sternomastoid muscle.

Neglected cases may lead to fibrosis and permanent shortening of sternomastoid muscle. This is an findication for surgical release. If left uncorrected it may progress to craniofacial growth asymmetry.