Light and electron microscopic evaluation of the pectoralis major muscle following tissue expansion for breast reconstruction

The placement of tissue expanders under the pectoralis major muscle has become a common procedure in breast reconstruction after mastectomy. Little information is available regarding the changes caused by tissue expansion on human skeletal muscle. In this study, we report the light and electron microscopic changes observed in 20 expanded pectoralis major muscles from 12 patients undergoing two-stage breast reconstruction procedures. Standard 400-cc round Radovan tissue expanders were placed, eight bilaterally and four unilaterally. Three biopsies were taken from each muscle at different locations during both the first stage (pre-expansion) and 23 weeks later at the second stage (postexpansion). The operative procedures and expansion protocol were the same in all reconstructions. No postoperative radiation therapy was added. The histologic changes were reported in a blind fashion by one pathologist. Light microscopy did not show significant pathologic changes. All but one of the pre-expansion specimens examined by electron microscope were reported as normal, whereas all of the postexpansion biopsies were grossly altered. Focal muscle fiber degeneration with glycogen deposits and mild interstitial fibrosis was noted. In addition, some fibers showed disorganization of the myofilaments in the sarcomeres. The above ultrastructural changes are significant morphologic alterations, which may be the result of muscle hypoxia. Whether these changes indicate permanent or transient transformation is yet unclear. Patient follow-up did not reveal any functional muscular deficit. We conclude that there is definite evidence to suggest significant muscular structural damage after routine subpectoral expansion for breast reconstruction.