Torticollis is a result of unilateral tightness and shortening of one sternocleidomastoid muscle. The earliest description of this condition dates back to writings from the ancient Greek civilization. According to Plutarch, Alexander the Great may have had torticollis.
Torticollis occurs in 0.4% of all births. A visible or sometimes palpable swelling, often referred to as a sternomastoid tumor, appears in a part of the muscle in infants aged 2-3 weeks. It often persists until they are aged 1 year. It is rarely bilateral and may be seen in older children in whom the mass was not previously identified.
An end-arterial branch of the superior thyroid artery supplies the middle part of the sternocleidomastoid; obliteration of this end artery may be responsible for the development of muscle fibrosis. (See the image below.) As an alternative, primary trauma that temporarily and acutely obstructs the veins may lead to intravascular clotting in the obstructed venous tree. In infants, this clotting is evidenced by the development of a sternocleidomastoid mass, which eventually disappears and is replaced by fibrous tissue.
Abnormalities in the basal ganglia may be involved in the pathophysiology of spasmodic torticollis.  On the other hand, some vestibular abnormalities have been reported that are not explainable solely as secondary to abnormal head and neck movements in spasmodic torticollis but seem to be more intimately related to its pathophysiology. In this respect, abnormal interaction of vestibular signals with higher-order motor commands and disrupted central vestibular processing (perhaps caused by subtle imbalances in the vestibular system) seem particularly important. 
The etiology of torticollis is incompletely understood, though several theories have been advanced. [3, 4] Reports on the familial transmission of congenital muscular torticollis have been few. An idiopathic intrauterine embryopathy or the intrauterine development of sternocleidomastoid compartment syndrome may be responsible for the sternomastoid fibrosis.
Recurrent torticollis after surgery is rare, with a frequency of approximately 5%.  Even in patients older than school age and those who have finished growth, sufficient unipolar or bipolar release of the sternocleidomastoid and intensive postoperative care can generally be expected to yield satisfactory treatment results. 
Secondary effects of untreated torticollis include the following:
Plagiocephaly is an asymmetric skull deformity in infants that is caused by flattening of one occiput that leads to secondary flattening of the contralateral forehead. After the torticollis resolves, the plagiocephaly resolves; however, several years may pass before it disappears.  Although torticollis can predispose to plagiocephaly without synostosis (PWS), torticollis appears to result from plagiocephaly in a large proportion of cases of plagiocephaly with scoliosis. 
Facial hypoplasia is inhibition in the growth of the mandible and maxilla due to muscle inactivity. Clinically significant facial hemihypoplasia develops over 8 months; however, it is obvious in patients at the age of 2-3 years. Facial hypoplasia improves as the child grows, after the torticollis resolves. 
Musculoskeletal effects include the compensatory ipsilateral elevation of the shoulder, as well as cervical and thoracic scoliosis. Wasting of additional muscles in the neck may be present as a consequence of sternocleidomastoid inactivity.
Congenital muscular torticollis has also been reported to be a significant risk factor for later neurodevelopmental conditions (eg, attention-deficit hyperactivity disorder [ADHD], developmental coordination disorder, language impairment, and autistic spectrum disorder), with disorders presenting at different stages of development.