An Incomplete Superficial Palmar Arterial Arch: Clinical Considerations of the Modified Allen's Test

The modified Allen's test (MAT) is a non-invasive test for evaluating the circulation of the hand, including the superficial palmar arch (SPA). However, although there are many variations of SPA, it cannot be said that it is widely recognized in clinical practice. Herein, we report an incomplete SPA observed in the right hand of an 83-year-old male cadaver. Notably, the superficial palmar branch of the radial artery ran superficial to the abductor pollicis brevis muscle, and no median artery was identified. Six common palmar digital arteries, that is, four from the ulnar artery and two from the radial artery, were observed. This anatomical configuration lacked an anastomotic connection between the radial and ulnar arteries, suggesting insufficient collateral circulation. As a result, performing the MAT in such a case may yield a "positive" result, indicating inadequate collateral blood flow. However, in the context of an incomplete SPA, this result may reflect a true anatomical limitation rather than a pathological arterial obstruction. Therefore, clinicians must consider underlying anatomical variations when interpreting MAT results. Supplemental diagnostic tools, such as Doppler ultrasonography or pulse oximetry, may help distinguish between anatomical variants and vascular pathology. Recognizing these variations is essential for accurate circulatory assessment and safe hemodynamic monitoring during anesthesia and other clinical interventions.