Answer: Fibromatosis Colli.
- Non-neoplastic SCM muscle enlargement in early infancy.
- Best diagnostic clue: Non-tender sternocleidomastoid muscle enlargement without discrete mass in an infant
- Mid to lower third of sternocleidomastoid muscle.
- Right > left; rarely bilateral.
- Oval or fusiform unilateral sternocleidomastoid muscle enlargement.
- No discrete mass or adenopathy.
- Best imaging tool: Ultrasound confirms clinical suspicion.
- Top Differential Diagnoses:
- Muscular Torticollis.
- Myositis Related to Neck Infection.
- Spinal Accessory Nodal Malignancy.
- Fibrocollagenous infiltration of SCM.
- When necessary, diagnosis can be confirmed by thin needle aspiration cytology.
- Possibly precipitated by in utero head position and SCM compartment syndrome.
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