Accurate diagnosis of isolated iliac vein thrombosis in third trimester pregnancy with clues on great saphenous vein reflux: a case report and review of literature

Pregnancy is a pro-coagulant state [4]. Combined with pregnancy-induced thrombophilia, venous stasis from the gravid uterus quadruples the incidence of DVT during pregnancy [5]. Unfortunately, most of the symptoms that raise suspicion of DVT or PE, such as swelling or pain in the legs, tachycardia, and dyspnea, represent benign physiological changes during pregnancy [6], and most patients with these symptoms will not have DVT or PE.

D-dimer is physiologically elevated during pregnancy, so its utility during pregnancy is limited to ruling out DVT. According to an analysis of a prospective study [7] evaluating the use of US for DVT diagnosis in pregnant patients using whole-blood agglutination D-dimer assays, the sensitivity of the assay was 100% (CI, 77–100%), the specificity was 60% (CI, 52–68%), and the negative predictive value was 100% (CI, 95–100%). Therefore, the diagnostic approach for VTE during pregnancy differs from that in non-pregnant individuals. The recommended initial diagnostic test is compression ultrasonography (CUS) when signs or symptoms suggest new-onset DVT [8]. In a review of published case series [9], in 88% of cases, DVT involved the left leg, and 46% of the described thrombosis was confined to the iliac and/or femoral vein. Notably, 12% of DVTs in pregnant women were isolated pelvic vein thrombosis compared to less than 1% in the non-pregnant population [10]. Left leg and proximal vein involvement in a pregnant patient supports the hypothesis of May–Thurner syndrome (MTS), also known as iliac vein compression syndrome, caused by the right thick-walled common iliac artery compressing the left thin-walled iliofemoral vein. Iliac vein thrombosis can be diagnosed by direct observation of echogenic masses in the cavity or the absence of spontaneous venous flow on Doppler examination (especially with augmentation maneuvers) [11]. Owing to obvious anatomical reasons, a CUS examination cannot be performed over the iliac veins. Because of the deep location, ultrasound imaging is less accurate for iliac vein thrombosis, especially in pregnant patients. In a study using MR imaging in pregnant women with CUS-proven DVT, CUS did not reveal concurrent pelvic vein thrombosis in 11% of patients [12]. When the iliac vein is blocked, blood flow from the lower limbs can bypass the branches of the great saphenous vein and return to the inferior vena cava. Vessels such as superficial circumflex iliac vein, superficial epigastric vein, and superficial external pudenal vein may form collateral circulation. Therefore, reverse blood flow occurs in the saphenous vein. In this case, the reflux in the saphenous vein lacks respiratory phasicity. This reflux is distinct from venous insufficiency with Valsalva response and respiratory phasicity (Figs. 5, 6 and 7). Flow that lacks respiratory phasicity and is not stopped by proximal compression or Valsalva maneuver is called continuous flow [13]. Unilateral continuous great saphenous vein reflux is suggestive of iliac veins obstruction or extrinsic compression. The imaging of reflux in the great saphenous vein may be integrated into the point-of-care clinical ultrasound protocol to predict iliac vein thrombosis during compression ultrasonography of the lower extremities.

The recommended treatment for thromboembolism in pregnant patients consists of weight-based unfractionated heparin or low-molecular weight heparin throughout pregnancy until at least 6 weeks postpartum [2]. The reduction of recurrent deep venous thrombosis or PE in patients who continued to anticoagulants was 64% compared with those taking placebo [14, 15]. In this case, the patient received low molecular weight heparin for anticoagulation, and no bleeding or bruising complications at the time of injection.

IVCF was widely used in the daily clinical practice to prevent PE. An inferior vena cava (IVC) filter can act as a mechanical barrier in the prevention of a lower extremity or pelvic venous thrombosis from embolising to become a potentially lethal pulmonary embolus. The intended dwell time of a temporary IVCF is 7 to 35 days. Complications of IVC filters include trauma at insertion, fracture and/or migration, occlusion by thrombus or endothelialisation, penetration of the IVC and failed retrieval [16].