Dynamic Entrapment Causing Bypass Graft Occlusion: Ultrasound Reveals an Unusual Cause of Flow Interruption

By: Ming Yeung

Aims To present a case of graft entrapment causing dynamic occlusion of a bypass graft and to demonstrate how duplex ultrasound, performed with slight positional variation, can uncover critical diagnostic findings when standard imaging fails to explain low graft flow. Methods A 60-year-old male underwent a right proximal superficial femoral artery (SFA) to proximal anterior tibial artery (ATA) bypass graft using a reversed great saphenous vein. Initial post-operative ultrasound surveillance demonstrated low flow velocities without any identifiable stenosis. A follow up scan was performed with knee alternately in flexion and full extension demonstrated position-dependent flow interruption. Results The initial post-operative ultrasound scan showed low velocities, raising concern for compromised graft function; however, no stenosis was detected at either anastomosis. At three months, the follow up duplex demonstrated improved velocities and triphasic waveforms consistent with a patent graft. However, positional ultrasound revealed that with full knee extension, flow ceased entirely, whereas flow resumed (peak systolic velocity 58cm/s) with slight knee flexion, indicating dynamic occlusion. Magnetic resonance angiography confirmed the graft was entrapped between the medial head of gastrocnemius and the hamstring tendon. Surgical release of the entrapment restored graft flow independent of knee position. Conclusion This case highlights the diagnostic value of positional duplex ultrasound in identifying rare, dynamic causes of graft occlusion not apparent on routine imaging. When persistently low flows are observed in absence of stenosis, graft entrapment - although uncommon – should be considered. Attention to scanning technique and experience interpretation are essential in detecting such unusual postoperative findings.