Sternocleidomastoid tumour:

This is  due to the bleeding within the sternicleidomastoid  muscle caused by the injury during difficult delivery. The formation of hematoma within the sternocleidomastoid  further damages the muscle causing ischemia. Ultimately the fibrous tissue replaces the ischemic fibres. This will produce congenital torticollis. Passive stretching will usually be effective in restoring the range of motion. This tumours may be present any where in the line of sternocleidomastoid.