CMT is a relatively common deformity amongst infants.The direct cause of CMT is contracture and shortening of the SCM as a result of muscle fibrosis;however, the reason for muscle fibrosis is unclear [5
]. Recently, it has been found that the extent of SCM fibrosis is closely related to a limitation in the birth canal and an abnormal fetal position [6
]. The basic pathologic changes in patients with CMT are stromal proliferation and SCM fibrosis. Electron microscopic observations have shownthat the proliferated stroma contains collagen fibers and fibroblasts, together with large numbers of myoblasts, myofibroblasts, and mesenchymal-like cells. Some researchers believe that the key factor underlying different clinical outcomes of neck masses is the ratio of fibroblasts to myoblasts at various phases of differentiation and degeneration [7
]. The mass will disappear if myoblasts inside the mass differentiate and develop, as during the embryonic period. If degeneration takes place in some parts of myoblasts, partial muscle contracture occurs. If degeneration occurs in the majority of myoblasts, fibroblasts produce large amounts of collagen, leading to scar-like contracture of the SCM and typically resulting in torticollis [8
]. The timing of CMT treatment in the recovery of muscle function is key to the outcome; the sooner treatment begins, the better the outcome is likely to be. Self-healing of CMT is possible in patients < 1 year of age, and conservative treatment may achieve satisfactory results at this stage. Therefore, most researchers suggest only performing surgery in patients >1 year of age [9
]. If a diagnosis of CMT is established early and conservative treatment is initiated quickly, the cure rate can be > 80%, and the prognosis is excellent [9
]. If contractures or local deformities of the SCM have already occurred, the prognosis is poor, even after surgical treatment [10
]. Ultrasound examinations can reveal abnormal thicknesses and echo signals in the SCM in patients with CMT during the early stage. Our study showed that as a diagnostic test for CMT, ultrasonography has a very high sensitivity and specificity, which makes ultrasonography a very effective diagnostic tool. In our study, ultrasound examinations revealed no abnormalities in four patients who were diagnosed with CMT after surgery. Surgery showed that fibrosis occurred at the insertion sites of the sternal and clavicular heads of the SCM. It is possible that the sonographer neglected to check the distal ends of the SCM during scanning, resulting in misdiagnosis. In patients with non-muscular torticollis, mild SCM thickening occurred in two cases without abnormal echo signals, and the patients were ultimately diagnosed with spastic torticollis; however, there were no abnormal echo signal inside the muscle. Therefore, the diagnosis of CMT should not be based only on change in SCM thickness, but changes in echo signals should also be taken into account.
We also demonstrated differences in the clinical characteristics of CMT between the early and the late stages. The major manifestation in the early stage is a neck mass, while the characteristics in the late stage include muscle tension, contractures, and reduced neck activity. The stage of the disease affects the selection of treatment methods, with rehabilitative therapy often selected in the early stage and surgical treatment in the late stage.
Most of the previous studies have reported that the following sonographic features of the affected SCM in patients with CMT: echogenicity; texture; motility; softness; and the transverse and longitudinal extent of the involvement [11
]. Although many reports have been published on the ultrasonographic features of CMT, studies differentiating such features between the early and late stages are rare. Because the clinical manifestations of the disease, the extent of fibrosis, and treatment methods differ by stage, differences in ultrasound features in the early and late stages are valuable to help assess the severity of the disease and select an appropriate treatment method. We found that sonographic features of patients in the early stage of CMT include local thickening of the SCM, and weak or uneven echoes. In the late stage of CMT, the affected SCM becomes thick or thin, and there are diffuse increases in echo signals or cord-like hyperechoic signals inside the muscle layer. Color Doppler ultrasonography revealed short rod- and cord-like blood flow signals inside the thickened SCM muscle in patients with early-stage CMT (age <1 year). This finding may be associated with the rich network of capillaries inside the reactive granulation tissue that is produced during delivery because of extension of the SCM muscle fibers under heavy loads from external forces and gravity [15
]. No significant blood flow signal was noted inside the affected SCM in patients with late-stage CMT (age ≥1 year),which may be associated with the organization of granulation tissue, increased fibrosis, and reduced number of blood vessels. The results of the current study suggest that the color Doppler presentation can help determine the stage of the disease and the extent of fibrosis [16
Some researchers have indicated that if there is persistent head tilting and notable neck inclination to the affected side (>15°), as well as muscle contractures or scleromas inside the muscle after 6 months of conservative treatment, surgery should be performed early [17
]. In patients with CMT and ultrasonographic manifestations of the late stage, such as diffuse increases in echo signals or cord-like hyperechoic signals inside the muscle layer which meant relatively severe fibrosis, surgical treatment is used in most cases.In agreement with Yu et al.
], for patients with facial deformities caused by CMT, we believe that early surgery should be performed, even at age ≤ 8 months of age. If fibrosis is seen in a patient > 1 year of age, surgery should be performed as soon as possible to prevent refractory facial and neck deformities. In the present study, ultrasound examinations showed diffuse hyperechoic signals of the SCM and notable neck inclination in 8 cases during the early stage. Surgical treatment was performed in these patients, and significant muscular fibrosis was found intra-operatively. This suggests that when an ultrasound examination reveals diffusely increased or cord-like hyperechoic signals inside the SCM lesion and no blood flow signal within the lesion, indicating significant SCM fibrosis, surgery rather than rehabilitative therapy should be offered, even if the patient is < 1 year of age. Thus, an ultrasound examination can guide treatment decisions for patients with CMT [19
Non-muscular torticollis may be life-threatening if not treated early. In the present study, the SCM echo signals were normal in patients with non-muscular torticollis, with the exception of one case with a slightly thickened SCM. Muscular torticollis and non-muscular torticollis can be differentiated by the combination of changes in SCM thickness and echo signals. An ultrasound examination can differentiate a mass from other types of masses, such as cervical cystic lymphangiomas and enlarged cervical lymph nodes, and thus has high clinical value [20