Demonstration of Unilateral Absence of the Palmar Arch Without Collateral Circulation
A 27-year-old surgical resident from South America noticed occasional tingling in her right hand on awakening. She performed a modified Allen test1 on her own hands and noticed a subtle line of demarcation on the palm of her right hand accompanied by induction of similar tingling sensations. The demarcation was not seen on the left hand. We suspected an incomplete palmar arch, and to better demonstrate these findings, we wrapped the patient’s right hand with a latex bandage to exsanguinate the extremity. Assistants applied pressure to both the radial and ulnar arteries at the wrist as the latex bandage was removed. Initially, the ulnar artery pressure was released while we maintained an occlusive force on the radial artery. The dramatic visual results of the Allen test can be seen in the photograph (Figure 1). In addition, the subject complained of nearly simultaneous tingling and numbness in the ischemic radial artery distribution after arterial occlusion. The evaluation was then repeated to demonstrate the incomplete arch pattern with occlusion of the ulnar artery (Figure 2). The subject had some mild residual discomfort in her hand for the next 12 hours after the test-provoked ischemia, which subsequently subsided.
The Allen test, first described in 1929, was initially used to evaluate occlusive disease in the ulnar artery distribution and is used frequently as a bedside evaluation of collateral circulation of the hand.1 It is estimated that &50% of the population may have “incomplete” palmar arches, but we have no conclusive evidence about the percentage of the population that will have significant loss of flow through the superficial palmar arch region with occlusion of the radial artery.2 Considering that 27.5% of radial catheters cause abnormal radial artery flow with the potential for thrombosis, medical staff should be cognizant of the potential for ischemia due to this anatomic variance.3 In patients in whom signs or symptoms of ischemia are noted, immediate removal of the intra-arterial catheter is required, and further testing for adequate blood flow may be indicated. For patients having a radial artery harvest for coronary artery bypass grafting, a Doppler evaluation may be considered because of the equivocal nature of the Allen test in some patients who would ultimately not tolerate radial artery ligation.4,5