Cervical Spondylosis: This condition, which involves wear and tear on the discs in the neck, can cause pain in the neck, upper back, and refer pain to the shoulder and elbow due to nerve compression. The supraclavicular fossa enlargement could be due to muscle spasm or swelling in response to the cervical spine issues.

Thoracic Outlet Syndrome (TOS): This condition involves compression, injury, or irritation of the nerves and/or blood vessels (arteries and veins) in the thoracic outlet area, which lies between your collarbone (clavicle) and first rib. It can cause pain in the shoulders, neck, and upper back, and could potentially cause swelling or the sensation of enlargement in the supraclavicular fossa.
Costoclavicular Syndrome: Similar to TOS, this condition involves compression of the neurovascular bundle between the clavicle and the first rib, leading to pain and potentially swelling in the supraclavicular area, along with shoulder and elbow pain due to referred pain patterns.
Scalene Muscle Syndrome: This is another form of TOS, where the scalene muscles compress the nerves and/or blood vessels, causing similar symptoms to those described.

Pancoast Tumor: A type of lung cancer located at the top of the lung that can cause shoulder and arm pain, along with swelling in the supraclavicular fossa due to lymph node involvement or direct tumor extension. Although less common, missing this diagnosis could be fatal.
Aortic Dissection: A serious condition where there is a tear in the aorta's inner layer, which can cause severe, tearing chest pain radiating to the back, and potentially swelling or pain in the supraclavicular area if the dissection affects blood flow to the upper body.
Spinal Cord Compression: Conditions such as tumors, abscesses, or fractures can compress the spinal cord, leading to pain, neurological deficits, and potentially swelling in the supraclavicular area due to muscle spasm or referred pain.

Eagle Syndrome: A condition where an elongated or calcified styloid process irritates the surrounding nerves and tissues, causing pain in the face, neck, and ears, and potentially referred pain to the shoulder and elbow.
Cervical Rib: An extra rib that can cause TOS-like symptoms due to compression of the nerves and blood vessels between the cervical rib and the first thoracic rib.
Brachial Plexitis (Neuralgic Amyotrophy): An inflammatory condition affecting the nerves of the brachial plexus, leading to severe pain in the shoulder and arm, which could potentially cause swelling or the sensation of enlargement in the supraclavicular fossa due to inflammation.