What is the cause of congenital torticollis, is it ischaemia (lack of blood flow) or trauma leading to fibrosis (scarring) and contracture (muscle shortening)?

Congenital Torticollis: Etiology and Pathophysiology

Congenital muscular torticollis is primarily caused by fibrosis and contracture of the sternocleidomastoid muscle resulting from birth trauma or intrauterine ischemia leading to muscle injury and subsequent fibrotic changes.

Pathophysiological Mechanisms

Primary Causes

• Fibrotic changes in the sternocleidomastoid muscle (SCM) are the fundamental structural abnormality in congenital muscular torticollis 1
• The fibrotic process results in shortening of the SCM, creating an asymmetrical head position with lateral head tilt and chin rotation toward the opposite side 2
• Ultrasound examination reveals characteristic lesions showing homogeneous or heterogeneous hyperechoic areas within the SCM, representing fibrotic tissue 3

Birth Trauma Theory

• Children born via vaginal delivery more frequently develop left-sided torticollis with more significant broadening of the SCM, supporting the trauma theory 1
• Birth trauma may cause muscle injury leading to compartment syndrome, resulting in ischemia, necrosis, and subsequent fibrosis of the SCM 1, 2
• The mechanical forces during delivery may stretch or tear the SCM, initiating an inflammatory response that progresses to fibrosis 3

Ischemic Theory

• Intrauterine or perinatal vascular insufficiency to the SCM may lead to muscle ischemia 2
• The ischemic injury triggers an inflammatory cascade that ultimately results in fibrosis and contracture 4
• The extent of fibrosis correlates with clinical severity - larger cross-sectional involvement of the muscle (higher lesion-to-muscle ratio) predicts poorer outcomes and higher likelihood of requiring surgical intervention 3

Risk Factors and Associated Findings

• Male predominance with 54% of cases occurring in male infants 1
• Higher birth weight is associated with increased risk, particularly in male infants (p<0.05) 1
• 76% of pediatric patients with congenital muscular torticollis are born to first-time mothers 1
• Hip dysplasia coexists in approximately 10% of cases, making it an important associated finding to screen for 2, 5
• The right side is more commonly affected (59.3%) than the left side (40.1%) 3

Natural History and Progression

• Without treatment, the fibrotic process in the SCM may lead to persistent head tilt, facial asymmetry, and limited neck range of motion 4
• The extent of fibrosis naturally decreases over time - from 83.6% at 2 months to 59.9% at 9 months, and further to 40% beyond 1 year of age 3
• The decrease in fibrosis occurs due to increased normal muscle volume at the periphery and regenerated muscle fibers within the lesion 3
• Whole-length muscle involvement is a significant predictor of poor outcome - 34.7% of cases with entire length involvement required surgical intervention versus only 6.3% when limited to middle/lower thirds 3

Differential Diagnosis

• Ocular torticollis caused by eye muscle weakness 2
• Sandifer's syndrome resulting from gastroesophageal reflux 2
• Neural axis abnormalities 2
• Benign paroxysmal torticollis 2
• Atlantoaxial rotatory displacement 2
• Retropharyngeal abscesses 2
• Posterior fossa tumors 2

In conclusion, congenital muscular torticollis results from a combination of birth trauma and/or ischemic injury to the sternocleidomastoid muscle, leading to fibrosis and contracture. The extent and distribution of fibrotic changes within the muscle determine the clinical severity and prognosis. Early identification and intervention are crucial for optimal outcomes.