Thoracic outlet syndrome occurs when the blood vessels or nerves in the thoracic outlet - the space between the lower neck and upper chest - become compressed. This can cause pain and numbness in the shoulders and neck as well as reduced pulse. It is commonly caused by anatomical variations like cervical ribs or muscle abnormalities that reduce the space available to the neurovascular structures passing through. Diagnosis involves clinical tests like Adson's maneuver and imaging like MRI. Treatment ranges from physiotherapy and analgesics for mild cases to surgical removal of the first rib and scalene muscles for more severe or progressive cases.