Hydration Attenuates Incidental Iliac Vein Stenosis Detected by Magnetic Resonance Imaging in Deliberately Fasted Asymptomatic Individuals

ABSTRACTObjective Iliac vein stenosis (IVS) is observed in up to 30% of asymptomatic individuals, suggesting that it may represent a normal anatomic variant rather than a pathologic condition in these cases. This study aimed to examine the effect of intravascular hydration on the degree of IVS in deliberately fasted participants without venous symptoms. Methods This was a prospective, within-subject, analyst-blinded physiologic study conducted at a single, tertiary academic hospital from August 2022 to April 2024. Adult participants without venous symptoms were instructed to fast at midnight and to present the next morning for imaging. They underwent magnetic resonance imaging immediately before and after intravenous normal saline administration (1, 1.5, or 2 liters). Two independent reviewers measured the widest and narrowest areas of the bilateral common (CIV) and external (EIV) iliac veins using multiplanar reformatting. The primary outcome was the change in the proportion of participants with left CIV stenosis of ≥50% (defined by cross-sectional area) between pre-hydration and post-hydration MRI across all hydration volumes combined. Results Among 14 participants (median age, 30 years; 50% female; 71.4% white; 85.7% non-Hispanic), the median BMI was 26.3 IQR, 22.9-29.8. Across all hydration volumes combined, the proportion of participants with ≥50% stenosis of the left CIV decreased from 42.9% (n=6/14) to 7.1% (n=1/14) following hydration (p=0.025). The narrowest cross-sectional area of the left CIV demonstrated a substantially larger relative increase than the widest area (median IQR, +34.5% +21.0 to +76.3 vs. +8.4% +2.2 to +25.5, p=0.011), corresponding to a reduction in median stenosis severity from 45.7% to 36.9% (p=0.016). Hydration similarly increased both the narrowest and the widest areas of the right CIV, the left EIV, and the right EIV. For the right CIV, the increase was more pronounced at the narrowest area (+27.1% +9.7 to +45.0) compared to the widest (+17.6% +3.1 to +27.6; p=0.019). Neither hydration volume nor sex was associated with changes in cross-sectional area or stenosis in any iliac vein. Conclusions In deliberately fasted individuals, intravascular hydration increased left iliac vein size and reduced the apparent degree of IVS on MRI. Considering hydration status may reduce misclassification of physiologic iliac vein narrowing as pathologic IVS, and validation in symptomatic patients is warranted.