Aortocaval fistula is an uncommon clinical entity, usually associated with aortoiliac aneurysms. Clinical manifestations include abdominal pain, a pulsatile mass, and bruits, often accompanied by symptoms of high-output heart failure such as dyspnea, tachypnea, and peripheral edema. Endovascular therapy could serve as the preferred treatment, especially in patients with cardiac and pulmonary dysfunction. This report highlights a key clinical finding of aortocaval fistula— a pulsatile femoral vein— and propose a novel, simple, and radiation-free method to confirm or exclude the presence of a fistula postoperatively. Informed consent was obtained from the patient for publication of the case report and accompanying images. Institutional Review Board approval was waived due to the retrospective nature of the case report.

A 65-year-old man presented to the emergency department with acute-onset lower abdominal pain associated with a hard, blue penis, dysuria, hematuria, and subsequently warm and blue lower extremities. Initial laboratory findings revealed elevated levels of white blood cells (WBCs) (25,000/µL), urea (101 mg/dL), creatinine (4.7 mg/dL), lactose dehydrogenase (LDH, 283 U/L), creatine phosphokinase (CPK, 951 U/L), and troponin (TROP, 0.7 ng/mL). The patient’s medical history included hypertension, diabetes mellitus, and a stroke, experienced 3 years ago, with residual left hemiparesis. He had undergone endovascular repair of a right-sided popliteal aneurysm a few years prior, but was unaware of a concurrent abdominal aortic aneurysm.

Clinical examination revealed a pulsatile abdominal mass and edema of the lower extremities. The patient underwent an urgent computed tomography angiography (CTA) of the thoracic and abdominal aorta, which revealed an 8-cm abdominal aortic aneurysm, early contrast enhancement of the inferior vena cava, and dilated iliac and femoral veins (Fig. 1A).

Figure 1. Computed tomography scans at different time points. (A) At presentation. (B) Before discharge, showing a small type II endoleak (delayed phase). (C) At 6-months, demonstrating regression of the aneurysm sac (pre-contrast phase). (D) At 3 years postoperatively, showing complete regression of the aneurysm sac with no evidence of an endoleak.

The patient underwent urgent endovascular repair using the bilateral femoral artery cut-down technique and a Gore Excluder stent graft (oversized by approximately 20%, W. L. Gore & Associates) (Fig. 2). Owing to venous hypertension, pulsation was observed in the femoral veins until endograft deployment. The need for vasopressors and inotropes ceased immediately after the expansion of the endograft. The procedure was completed successfully, and the patient was admitted to the the intensive care unit for one day.

Figure 2. Angiography performed in the operation room before and after the placement of the endograft.

Pre-discharge imaging included CT and duplex scans. CT revealed a small endoleak, likely type II (Fig. 1B). A duplex scan at the rupture site (retroperitoneum) revealed pulsatile flow with a velocity of 14-17 cm/s, whereas the femoral vein velocities ranged from 6-13 cm/s with pulsatility (Fig. 3). The laboratory results before discharge showed normalization of the previously measured values: WBC count (10,000/µL), urea concentration (48 mg/dL), creatinine (0.48 mg/dL), LDH (150 U/L), CPK (116 U/L), and TROP (0.01 ng/mL). The patient had an uncomplicated postoperative course and was discharged 1 week after the operation.

Figure 3. First postoperative duplex scan of the femoral vein revealing abnormal arterial flow, which can be observed in the presence of an endoleak.

At the 6-months follow-up, a duplex scan of the femoral vein showed continuous, non-pulsatile flow (Fig. 4), and a CT scan confirmed the absence of an endoleak (Fig. 1C). At the 3-year follow-up, the aneurysm sac had reduced to a maximum diameter of 4 cm with no evidence of an endoleak (Fig. 1D). Venous duplex ultrasound continued to demonstrate a continuous, non-pulsatile flow.

Figure 4. Second duplex scan of femoral vein at the 6-month follow-up revealed continuous, non-pulsatile flow.

Aortocaval fistula is a rare clinical entity characterized by an abnormal communication between the aorta and the inferior vena cava. It can be primary, such as the presence of abdominal aortic aneurysms, or secondary, following aortic or other surgical operations [1,2]. Clinical manifestations include a pulsatile abdominal mass; symptoms of high-output cardiac failure including dyspnea, fatigue, tachycardia, and hypotension; lower extremity congestion; and an abdominal bruit. Ben Abdallah et al. [3] presented a case of phlegmasia cerulea dolens resulting from an aortocaval fistula.

Diagnosis relies on thorough clinical examination and CTA. CTA provides detailed anatomical information, aiding treatment planning and identifying complications such as thrombosis or pulmonary embolism. Currently, endovascular therapy is the preferred approach for anatomically feasible patients since it is also used to treat ruptured abdominal aortic aneurisms (rAAAs). For rAAAs, a graft oversizing of 30% is recommended because of potential inaccuracies in aortic measurements resulting from hypotension and hypovolemia [4,5]. However, in cases of aortocaval fistula, where hypotension occurs without hypovolemia due to blood diversion into the venous system, a standard oversizing of 20% may be typically sufficient, as demonstrated in our patient. However, no specific guidelines are available regarding oversizing in this condition.

In a recent systematic review regarding the outcomes after endovascular aneurysm repair (EVAR) for aortocaval fistula, Dakis et al. [6] reported an endoleak incidence of up to 39.5%. The reintervention rate was estimated to be within 35.7%-50% after EVAR [6,7]. A possible explanation for the high percentage of endoleaks is that EVAR isolates the aneurysm from the circulation but does not address the fistula, which remains open as a continuous pathway between the aneurysm sac and the inferior vena cava. In cases of endoleak associated with heart failure or pulmonary embolism, closure of the fistula via embolization, plug insertion, or stent grafting of the inferior vena cava may be necessary [8]. This underscores the importance of long-term follow-up.

CTA offers high-resolution images and enables rapid and efficient diagnosis. However, its limitations concerning radiation exposure and contrast-related risks should be carefully considered and balanced according to the clinical needs of the patient. Duplex scanning of the aorta also provide valuable information for follow-up. However, it has some limitations, such as operator dependency and limited visualization in patients with obesity.

In this case report, we propose duplex ultrasound of the femoral veins as a complementary tool for assessing aortocaval fistulas during follow-up. This method is easier to perform in obese patients than aortic duplex scans, is less time-consuming, and provides valuable diagnostic information. It can identify abnormal venous patterns, such as increased velocity and pulsatile venous flow, suggesting the presence of an arterial-to-venous shunt. Additionally, it allows monitoring of femoral venous flow changes over time, offering insights into fistula stability, regression, or progression.

In our patient, abnormal femoral vein velocities and pulsatility 1-week postoperatively corresponded with a small type II endoleak, which resolved on subsequent follow-up examination. Duplex ultrasound of the femoral veins can reduce reliance on repeated CT scans by ruling out (or suspecting) a significant endoleak affecting the aneurysm sac and venous system. However, it should be noted that this method cannot replace CT. A limitation of this method is that it is an indirect method of diagnosis because it does not visualize the fistula itself (size and location), and it cannot be used for further investigation (e.g., preoperative planning). Therefore, it is a valuable adjunct rather than a substitute for other modalities.

The pathophysiology and remodelling of the aorta after EVAR for aortocaval fistulas need to be elucidated. In this case, it is suggested that early postoperative pulsatile flow in the femoral vein was caused by a residual type II endoleak, which disappeared when the endoleak ceased. The differential diagnosis included residual heart failure induced by an aortocaval fistula. Heart failure might have gradually improved after the fistula was corrected, resulting in the normalization of the femoral vein waveform over time. Further consultation by cardiologists using other diagnostic modalities (echocardiography), involving larger samples of patients with and without endoleaks after endovascular repair of aortocaval fistulas, would help determine the exact cause of this finding. In addition, an interesting article by Greenfield et al. [9] suggested that persistent type II endoleak, by draining into the inferior vena cava and facilitating depressurization of the aneurysmal sac, may play a role in promoting greater sac shrinkage.

Finally, the observation of pulsating femoral veins highlights the need for femoral cut-down or careful ultrasound-guided puncture of the femoral artery during EVAR. Inadvertent puncture of the femoral vein could result in significant blood loss and large hematoma formation.

In summary, this report proposes duplex scanning of the femoral vein as a follow-up method for an aortocaval fistulas. The presence of arterial-like flow in duplex scans of the femoral vein serves as an innovative, indirect, radiation-free, and noninvasive indicator for detecting endoleaks or persistent aortocaval fistulas. While it cannot entirely replace other diagnostic modalities, it can play an important adjunctive role in overall patient assessment.

None.

The authors have nothing to disclose.

Concept and design: CA, AM. Analysis and interpretation: CA, VI, SA, CG. Data collection: VI, FS, SS, CG. Writing the article: CA, AM. Critical revision of the article: FS, SA. Final approval of the article: all authors. Statistical analysis: none. Obtained funding: none. Overall responsibility: AM.