Thoracic Outlet Duplex Ultrasound
Thoracic outlet syndrome is a condition whereby symptoms such as neck, shoulder and arm pain, numbness or impaired circulation to the arms are produced from compression of the nerves, blood vessels or both. This compression is caused by an inadequate passage way through an area between the base of the neck and the armpit. This is called the thoracic outlet. The thoracic outlet is surrounded by muscle, bone and other connective tissue. Any condition that results in enlargement or displacement of the tissues within or surrounding the thoracic outlet can cause compression of the neurovascular bundle running through this outlet. Muscular growth from weightlifting, injuries (both acute and chronic), weight gain, an extra or abnormal rib (cervical rib) and in rare cases, tumour can all cause thoracic outlet syndrome. Thoracic outlet compression of the subclavian vein should be considered for patients presenting with ipsilateral arm swelling and unexplained occlusion of the SCV.
Duplex ultrasound is used to assess the subclavian and axillary arteries/veins as they travel through the thoracic outlet. These arteries/veins are first examined with the arm relaxed and dependant and are assessed for patency and to determine if there is any fixed abnormality, dilation or stenosis. Peak systolic velocities are measured throughout these arteries as a baseline for comparison during PSV measurement with arm movement.
The arteries/veins are examined as the patient slowly abducts (raises) their arm and finally as they place their arm in the military brace position. Direct visualisation of these arteries/veins during arm manipulation allows for comment upon whether compression of these arteries/veins occurs and if compete occlusion occurs. The degree of abduction required to compress these vessels can be documented. The increase in peak systolic velocities as the vessels are compressed can be documented.
Popliteal Artery Entrapment Duplex Ultrasound
Popliteal artery entrapment syndrome (PAES) is a caused by abnormal positioning of the popliteal artery in relation to its surrounding structures. The popliteal artery may have an atypical course or there may be atypical muscular insertion in the popliteal fossa. One or both of these occurrences can lead to extrinsic compression of the popliteal artery and in time may cause aneurysmal dilation, thrombus and embolism and stenosis. This may result in limb ischemia. Most cases or PAES occur in young sportsmen or soldiers whose well developed muscular of the legs can lead to exacerbation of the consequences of the anomalous relationship between muscle and artery.
Another form of PAES is called functional PAES. This occurs not because of anatomical abnormalities but due to the increased muscularity of the patient’s calf causing compression of the popliteal artery when the patient is plantar or dorsi flexing the foot.
Duplex ultrasound can be used to diagnose PAES. The arteries of the leg are imaged to assess for patency and to exclude atherosclerosis. The popliteal artery is assessed for aneurysmal dilatation and stenosis. An abnormal course of the popliteal artery can be documented. When assessing functional PAES the patient is examined lying supine with the foot extended over the edge of the bed. The popliteal artery is imaged with the foot in a neutral position and is then imaged when the patient is actively plantar flexing and dorsi flexing the foot. This is performed against and not against resistance. Significant compression and occlusion of the popliteal artery is often seen, particularly at the level of head of tibia. The amount of effort that is needed to compress and occlude the popliteal artery with plantar/dorsi flexion varies between individuals.
A stress exercise ABI study is helpful in determining whether a patient is experiencing claudication at the time of exercise.
False Aneurysm Duplex Study
When a patient has an angiogram, balloon angioplasty or stent the most common site for catheter access are the common femoral artery in the groin and the brachial artery in the arm. Upon removal of this catheter the hole that has been made in the artery wall may not adequately close. This allows blood to escape from the artery and creates a cavity in the tissue close to the artery that is called a false aneurysm. Ultrasound is commonly used to assess the site of the false aneurysm and measure the size of the false aneurysm and the size of the neck of the aneurysm. If the false aneurysm is very large, surgical repair of the damaged artery wall may be needed. Ultrasound can also be used to compress the neck of the false aneurysm until the blood within the aneurysm is thrombosed.