Thoracic outlet syndrome is a disease of extrinsic compression of the neurovascular structures thoracic outlet. And Congential Muscle abnormalities like those of the Omohyoid Muscles can cause e.g compressions of the subclavian vessels against the first rib!
http://medicine.hsc.wvu.edu/Surgery/MediaLibraries/Medicine-Surgery/Media/Documents/PDFs/Vascular/Presentations/Thoracic-Outlet.pdf