Quadrilateral Space Syndrome Sherry-Ann N. Brown, MD, PhD, Derrick A. Doolittle, MD, Carol J. Bohanon, DNP, RN, FNP-BC, Arjun Jayaraj, MBBS, Sailendra G. Naidu, MD, Eric A. Huettl, MD, Kevin J. Renfree, MD, Gustavo S. Oderich, MD, Haraldur Bjarnason, MD, Peter Gloviczki, MD, Waldemar E. Wysokinski, MD, PhD, Ian R. McPhail, MD  Mayo Clinic Proceedings  Volume 90, Issue 3, Pages 382-394 (March 2015) DOI: 10.1016/j.mayocp.2014.12.012 Copyright © 2015 Mayo Foundation for Medical Education and Research Terms and Conditions

Figure 1 Diagnosis and treatment algorithm for patients with suspected QSS (alternative diagnosis must also be excluded). AER = abduction and external rotation; CTA = computed tomography angiography; DSA = digital subtraction angiography; MRA = magnetic resonance angiography; nQSS = neurogenic quadrilateral space syndrome; NSAID = nonsteroidal anti-inflammatory drug; Overhead athlete = any patient engaged in elite, collegial, professional, or dedicated sport or activity involving repetitive abduction and external rotation of the arm above the head; PCHA = posterior circumflex humeral artery; PT = physical therapy; QS = quadrilateral space; QSS = quadrilateral space syndrome; SOL = space-occupying lesion; UEA = upper extremity arterial; US = ultrasound; vQSS = vascular quadrilateral space syndrome. ∗Ultrasound imaging has been preliminarily studied for the diagnosis of nQSS; there have not yet been studies specifically assessing ultrasound use to diagnose vQSS. ∗∗Electromyography has poor sensitivity for nQSS, but can rule out alternative diagnoses. Mayo Clinic Proceedings 2015 90, 382-394DOI: (10.1016/j.mayocp.2014.12.012) Copyright © 2015 Mayo Foundation for Medical Education and Research Terms and Conditions

Figure 2 Angiography of the right hand for patient 1. A, Angiogram of the right forearm on day 1 demonstrates occlusion of the proximal ulnar artery (solid arrow) and proximal interosseous arteries with distal reconstitution. The radial artery occlusion (dashed arrow) begins in the mid forearm. B, Angiogram on day 1 demonstrates poor or absent contrast filling of the ulnar (solid arrow) and radial (dashed arrow) arteries, as well as common digital arteries (smaller double arrows) due to embolization. C, Angiogram after surgical intervention 7 days after the first angiogram (panels A and B) demonstrates overall improved flow into the hand with partial revascularization of the ulnar (solid arrow) and radial (dashed arrow) arteries, as well as common digital arteries (smaller double arrows). Mayo Clinic Proceedings 2015 90, 382-394DOI: (10.1016/j.mayocp.2014.12.012) Copyright © 2015 Mayo Foundation for Medical Education and Research Terms and Conditions

Figure 3 Angiography of the right shoulder for patient 1 showing abrupt occlusion of the PCHA (arrow) caused by thrombus. PCHA = posterior circumflex humeral artery. Mayo Clinic Proceedings 2015 90, 382-394DOI: (10.1016/j.mayocp.2014.12.012) Copyright © 2015 Mayo Foundation for Medical Education and Research Terms and Conditions

Figure 4 Proposed mechanism for PCHA aneurysmal degeneration and thrombosis: the PCHA stretches around the neck of the humerus analogous to a taut stretched rubber band leading to intimal injury and weakening of the vessel wall (inset circle A); the repetitive pulley movement likely leads to turbulent blood flow within the “bend” PCHA around the humeral neck (inset circle B); vessel injury from these changes leads to subsequent aneurysmal degeneration and thrombosis (inset circles C and D). AER = abduction and external rotation; PCHA = posterior circumflex humeral artery. Mayo Clinic Proceedings 2015 90, 382-394DOI: (10.1016/j.mayocp.2014.12.012) Copyright © 2015 Mayo Foundation for Medical Education and Research Terms and Conditions