Here, we report an interesting case of bilateral fibrous structures found in the costoclavicular space of a 58-year-old male cadaver during routine anatomical dissection. On the left side, a strong fibrous band extending between the inferior surface of the lateral two-thirds of the clavicle and the coracoid process to the medial end of the first rib was found. On the right side, a similar but thinner structure was discovered. On both sides the variant fibrous structures replacing the subclavius muscle, reduced the costoclavicular space thus led to a possible entrapment site for the brachial plexus and the subclavian/axillary vessels, and may be involved in the development of thoracic outlet syndrome.
