Page 183 - Libro 2

10 — Upper Extremity Arterial Duplex Scanning
163
THORACIC OUTLET SYNDROME
Impingement of the neurovascular bundle as it tra- verses the confines of the thoracic outlet can cause symptoms related to the compression of the brachial plexus or vascular structures, but rarely both at the same time. Compression of structures in the thoracic outlet may be secondary to cervical ribs, abnormal fibrous bands, and possibly hypertrophy of the sca- lene muscles.
Symptoms of pure neurogenic TOS consist of pain, weakness, and muscle atrophy. A definitive diag- nosis is made by appropriate history and physical combined with electromyography (EMG) or nerve conduction studies. Demonstration of positional sub- clavian artery occlusion with an arterial duplex is often used as “supportive evidence” of neurogenic TOS because impingement of the subclavian artery is thought to suggest impingement of the adjacent neural tissues at the thoracic outlet. However, these provocative maneuvers are not specific, and subcla- vian artery occlusion can be demonstrated in up to 20% of normal individuals.9 There is no convincing evidence that arterial duplex can or should be used to confirm neurogenic TOS.
Venous TOS is another variant of thoracic outlet syndrome. Patients present with swelling of the arm due to venous obstruction and/or thrombosis. Chap- ter 15 discusses the venous duplex ultrasound proce- dures used in assessing the upper extremity venous system.
Major arterial thoracic outlet syndrome occurs primarily in younger patients. Large cervical ribs or clavicular abnormalities secondary to prior trauma can compress and damage the subclavian artery. This repeated trauma can result in a sub- clavian artery aneurysm, stenosis, ulceration, or occlusion of the subclavian artery. All of these ab- normalities can be the source of acute or chronic distal embolization to digital and palmar arteries. In more advanced cases, even occlusion of the brachial, axillary, and/or forearm arteries can oc- cur, all of which can be detected by arterial duplex scanning.
Arterial duplex or plethysmographic findings sug- gestive of asymmetric digital artery occlusion should prompt a search for a proximal embolic source. Du- plex ultrasound can readily identify subclavian ar- tery aneurysms and significant occlusive lesions. However, emboli can also result from seemingly trivial lesions. Slight areas of luminal irregularity are not definitively excluded by arterial duplex scan- ning. When there are unilateral digital artery occlu- sions and negative proximal arterial duplex studies, arteriography or intravascular ultrasound (IVUS) is indicated to definitively rule out a proximal arterial source of emboli.
Some patients with positional occlusion or steno- sis of the subclavian artery may be quite symptom- atic with activity, especially when working with their arms overhead. In such cases, the subclavian artery is compressed between the clavicle and first rib when the arms are abducted for overhead activity. Duplex or plethysmographic techniques can be used to demonstrate positional changes in distal arterial waveforms. It is uncommon for this so-called arterial minor form of TOS to result in damage to the arte- rial wall or to cause distal embolization. Treatment is only indicated in severely symptomatic patients. Treatment consists of first rib resection without arte- rial reconstruction.
Even though upper extremity arterial duplex is not indicated in the evaluation of neurogenic TOS, pro- vocative maneuvers in an attempt to elicit vascular compromise as supportive evidence for possible neu- rogenic TOS are widely practiced. Patients are exam- ined with a series of provocative positional changes in an attempt to provoke and therefore detect sub- clavian artery compromise. Other noninvasive vas- cular lab techniques, including segmental pressures with pulse volume recordings (PVRs) and/or digital photoplethysmography (PPG), may also be used with these maneuvers. Chapter 8 provides a complete re- view of these maneuvers.
TRAUMA
Currently, the standard of care for identifying a clini- cally significant vascular deficit in the setting of arterial trauma is arteriography or direct surgical exploration. There is a benefit in performing screening arterial du- plex examinations in patients with a normal physical exam but with a history of blunt or penetrating trauma distal to the axillary crease. One study evaluated 198 patients with 319 potential vascular injuries to the neck or extremities. The mechanism of injury was gunshot wounds in 62%, stabbings in 17%, and blunt trauma in 21%. All patients were hemodynamically stable without a clinically obvious arterial injury. Arterial du- plex studies correctly diagnosed 23 vascular injuries with 2 false-negative studies, neither of which required intervention, giving a sensitivity of 95% and specificity of 100%.10
Another study evaluated upper extremity trauma pa- tients with diminished extremity pulses. Fifty patients underwent extremity arterial duplex ultrasound fol- lowed by confirmatory angiography and/or surgical ex- ploration with a 100% sensitivity and specificity.11 In a follow-up cohort of 175 patients, the same authors used duplex ultrasound as the sole imaging modality and diagnosed 18 injuries. Seventeen of these were later confirmed by angiography and/or surgery. This study gives further evidence that duplex ultrasound serves