Abstract
While congenital muscular torticollis (CMT) can occur along with other conditions, such as clavicle fracture or brachial plexus injury, these conditions exist outside the sternocleidomastoid muscle (SCM). We present a rare case with concurrence of CMT and a malignant tumor inside the same SCM, along with serial clinical and radiological findings of the atypical features of CMT. The malignant tumor was in fact a low-grade fibromyxoid sarcoma. To the best of our knowledge, the current case is the first of a concurrent condition of CMT inside the SCM. This case suggests that concurrent conditions could exist either inside or outside the SCM with CMT. Therefore, a thorough evaluation of SCM is required when subjects with CMT display atypical features, such as the increase of mass or poor response to conservative therapy. In that case, appropriate imaging modalities, such as ultrasonogram or magnetic resonance imaging, are useful for differential diagnosis.