Coronavirus disease 2019 (COVID-19) is associated with significant thromboembolic risk. Extensive deep vein thrombosis can infrequently progress to phlegmasia cerulea dolens that carries high morbidity and mortality rates. We report a case of a middle-aged male presenting with phlegmasia cerulea dolens in the context of COVID-19 and underlying May-Thurner syndrome, associated with transiently positive antiphospholipid antibodies.

Deep venous thrombosis (DVT) is the most common cause of unilateral lower limb swelling. Common differential diagnosis includes superficial thrombophlebitis and ruptured Baker's cyst. DVT is one of the most common complications diagnosed following lower extremity orthopedic surgery. However, many less frequent causes are often easily overlooked. Here we present a case of a 65-year-old man with a previous hip replacement who developed left-sided progressive leg swelling for years, which was managed initially with anticoagulation for provoked DVT and with compression stockings for post-thrombotic syndrome with no improvement. There was arterialization and spectral broadening of the venous waveform in the Doppler study. Computed tomography angiogram of the lower limbs showed evidence of arteriovenous fistula (AVF) with opacification of the deep left leg veins. Angioplasty and embolization of the fistula resulted in the resolution of leg swelling. We also discussed similar cases found in the literature. AVF needs to be considered in patients presenting with unilateral leg swelling following lower extremity orthopedic surgery.