Pathophysiology of congenital anomalies in thoracic outlet syndrome.

Careful anatomic studies during 1,120 operations for thoracic outlet syndrome indicate that most TOS patients have anomalous fibromuscular bands near the brachial plexus and subclavian vessels that predispose them to neurovascular symptoms in the shoulder and upper extremity. Nine different types of these "soft tissue" anomalies not visible on roentgenograms have been identified during these operations. The anomalies often are multiple, and may or may not be associated with bone abnormalities as well. These anomalies are clearly associated with the symptoms of thoracic outlet syndrome, particularly the neurologic type, as they apparently irritate or compress the brachial plexus. Thus, it finally becomes clear why the majority of symptoms of TOS are neurologic in nature, rather than vascular, and why the positional pulse tests and arteriograms, strongly advocated in the past for this diagnosis, have proved generally unreliable. Furthermore, the anomalous bands explain why the electromyogram and nerve conduction tests are of little benefit in establishing the accurate diagnosis of TOS. They even indicate the most reliable clinical tests to establish the diagnosis, and dictate the most appropriate surgical procedures required to offer permanent relief. If patients with shoulder, arm and hand symptoms are carefully evaluated with appropriate tests, and then highly selected for surgical treatment after conservative measures fail, gratifying relief may still be obtained in over 90% of patients with severe thoracic outlet syndrome, providing the diagnosis is correct, and the proper operation is performed with great care.