Which anatomical structure is most likely to be affected by a cervical rib?

A cervical rib is an extra rib that can develop from the seventh cervical vertebra. Its presence can lead to various complications, particularly concerning the structures in its vicinity.

The subclavian artery, which supplies blood to the upper limb and part of the thorax, runs near the first rib and can be compressed by an abnormal cervical rib. This compression can lead to vascular symptoms in the arm. Similarly, the brachial plexus, which is a network of nerves that innervates the upper limb, can also be affected by a cervical rib. A cervical rib can cause nerve compression, leading to pain, weakness, or numbness in the affected arm.

Considering this, the presence of a cervical rib is likely to impact both the subclavian artery and the brachial plexus. Therefore, the correct choice highlights that both of these critical structures are at risk of being affected by the anatomical alterations introduced by a cervical rib. These combined effects make answer choice detailing both the subclavian artery and brachial plexus the most accurate and appropriate response.