Sternocleidomastoid pseudotumor of infants and congenital muscular torticollis: Fine-structure research

Fifty cases, 16 with sternocleidomastoid pseudotumor of infants (SCMPOI) an d 34 with congenital muscular torticollis (CMT), were investigated by light and electron microscopy. The ultrastructure of the pseudotumor revealed th at there were myoblasts, fibroblasts, myofibroblasts, and mesenchyme-like c ells, which consisted of fibrous tissue and were regarded as fibroblasts on ly in the literature. The myoblasts showed the various stages of differenti ation and degeneration. For those cases without mass, the collagen fibrils and fibrocytes were often arranged in tight parallel bundles in which some muscles showed normal structure and some with decreased myofibrillae. The m esenchyme-like cells and myoblasts found in the pseudotumor may be the key point to its pathologic characteristics.