Morphometric evaluation of the left inferior phrenic vein in patients with portal hypertension

We reviewed venograms during BRTO for morphometric assessment of LIPV in patients with portal hypertension. All LIPV phlebograms showed narrowing just above the common trunk. The diameter of the LIPV and the narrowed LIPV were significantly larger in men than in the women, while no significant difference was observed in the rate of narrowing or the distance between the narrowed LIPV and the left renal vein.

LIPV is rarely discussed in classical anatomy textbooks16. However, in recent years, with the development of endoscopic and endovascular treatments for esophageal and gastric varices, LIPV, which serves as an important portosystemic shunt in patients with portal hypertension, is attracting more and more attention.12,17,18,19. Loukas et al. classified and described variations in the origins and distributions of LIPV in cadavers19. Among 300 cadaver specimens, 37% of LIPV drained into the IVC below the diaphragm, 25% into the left adrenal vein, 15% into the left renal vein, 14% into the left hepatic vein, and 1% both into the VCI and left. adrenal vein. On the other hand, Araki et al. reviewed phlebograms obtained from adrenal vein sampling and reported that the LIPV fused with the left adrenal vein in 92.8% of cases, and the mean distance from the confluence to the renal vein was 16.4 mm , with a standard deviation of 4.7 mm12. They also noted that 87.2% of patients without portal hypertension had narrowed LIPV, which was presumably formed by the valves. Saad et al. reviewed the BRTO technique and reported a web-like narrowing at the junction of the LIPV with the common trunk, which made catheter insertion difficult11.

The present study is the first to describe the morphometric characteristics of LIPV and its shrinkage. Since the LIPV serves as a major portosystemic shunt, it was hypothesized that the diameter of the LIPV correlated with the severity of portal hypertension. However, only total bilirubin level and Child-Pugh score correlated with LIPV diameter in the present study. Other factors should be considered to determine the association between LIPV diameter and portal hypertension, including portal blood flow, portal pressure, and degree of development of collateral pathways.

The results revealed the presence of a narrowing just above the common trunk of LIPV. There were no significant differences in LIPV diameter or shrinkage rate between venograms and axial CT images. In contrast, the diameter of the narrowed LIPV was significantly larger on CT images (6.1 ± 2.3 mm) than on venograms (5.1 ± 2.3 mm) (p= 0.03). However, since the 95% confidence interval was -1.65 to 0.098 mm, the difference in diameter of the narrowed LIPV between venograms and CT images was not considered clinically significant.

The mean distance between the narrowed LIPV and the left renal vein was 20.0 mm with a standard deviation of 7.4 mm. This was longer than previously reported by Araki et al.12, and can be attributed to differences in patient characteristics. The study by Araki et al. examined patients without portal hypertension, whereas we studied and obtained measurements in patients with portal hypertension. The LIPV may be dilated and tortuous in patients with portal hypertension and therefore the distance between the narrowed LIPV and the left renal vein may be longer.

Based on the results obtained, in BRTO, careful manipulation of the catheter is required to pass through a narrowing of the LIPV located approximately 2 cm from the left renal vein. Once a catheter passes, the narrowing provides a very effective choke point11. In BRTO, it is critical for successful treatment that GRS be completely balloon occluded before injecting sclerosant into the gastric varices. A balloon placed just above the stricture may be stable and adequately occlude the GRS10.11.

This study has some limitations. First, the sample size was small. Second, LIPV venograms during BRTO were obtained following manual contrast injection to prevent vein rupture. Differences in contrast volume and injection speed can affect LIPV performance and shrinkage. Additionally, we hypothesized that the LIPV stricture was formed by venous valves (downflow valves), which was consistent with the reason for the difficulty in passing the catheter over the stricture. However, the presence of venous valves has not yet been confirmed histologically; therefore, further investigation of the cadavers is required.

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