Ultrasound Imaging of the Brachial Plexus Sheath and Its Fascial Compartments at the Costoclavicular Space and Infraclavicular Fossa

The existence of the brachial plexus sheath (BPS) and its septae and compartments has been a subject of debate and controversy. Numerous cadaver studies indicate that BPS is present while other researchers based on limited clinical data suggest none. Nevertheless, cumulative evidence over the last six decades indicate that it is multi-layered, fibrous and a web-like connective tissue that is derived from the deep cervical fascia and fused with the deep fascia of the arm The BPS completely envelopes that neurovascular bundle and filed with loose connective tissue and fat. It is a multi-compartment structure in the axilla with each nerve having a separate compartment, that communicate with each other. Some studies suggested that the septae affect the spread of local anesthetic during an axillary or infraclavicular brachial plexus block, while some suggest the opposite. With the use of ultrasound imaging, researchers found the presence of this connective tissue septum within the BPS at the costoclavicular space and infraclavicular fossa. The septum is visualized as a linear hyperechoic band on ultrasound imaging and when present appears to reduce the spread of the drugs during brachial plexus block. Yet the anatomy is poorly seen with the previous generation of ultrasound imaging. The aim of this study is to define the connective tissue (fascial) layers that surround the brachial plexus and its septum at the infraclavicular fossa by reviewing our archived high definition ultrasound images of 100 patients who had successfully undergone the ultrasound guided brachial plexus block over a 5 year period (2013 to 2018).