Hemodynamic evolution of umbilical-portal stenosis mimicking portal vein agenesis: description of a prenatal case

Congenital anomalies of the fetal portal venous system (PVS) present a significant challenge in prenatal sonography due to their complex spectrum of presentations. A prenatal diagnosis of portal vein agenesis (PVA) is often associated with a poor prognosis and may lead to pregnancy termination. We describe a diagnostic pitfall in which severe umbilical-portal stenosis with systemic shunting mimicked PVA. This case illustrates the spontaneous resolution of such hemodynamic alterations, highlighting the importance of differentiating between functional stenosis and anatomical agenesis through longitudinal quantitative assessment.

A 35-year-old woman (gravida 4, para 1), pregnant via in vitro fertilization, presented at 23 weeks of gestation for anomaly scanning of a dichorionic diamniotic twin pregnancy. Ultrasonography was performed using a GE Voluson E10 system (GE Healthcare, Zipf, Austria) equipped with a C1–5 convex transducer. Fetus A exhibited normal growth and anatomy, serving as a physiological internal control. However, in Fetus B, the PVS (including the left, right, and main portal veins, and ductus venosus) was poorly visualized, with a paucity of flow signals on high-definition flow imaging, highly suggestive of PVA (Figure 1A). Concurrently, biometry revealed that Fetus B was smaller than Fetus A (discordance of ~17%), consistent with potential vascular compromise.

Figure 1 Prenatal hemodynamic assessment of Fetus B at 23 weeks. (A) High-definition flow imaging of the upper abdomen showed sparse flow in the portal veins with non-visualization of secondary branches, initially mimicking agenesis. (B) Magnified view of the UPJ. The arrow highlights a focal high-velocity jet (aliasing) penetrating the critical stenosis. (C) Visualization of the primary systemic shunt, where the dilated UV drains directly into the LCIV (arrow). (D) An additional collateral pathway was detected, showing diversion of blood flow through a thoracic wall vein toward the right atrium (arrows). (E) Dilated IVC indicating volume overload. (F) Compensatory HA dilatation. BL, bladder; GB, gallbladder; HA, hepatic artery; IVC, inferior vena cava; LCIV, left common iliac vein; LPV, left portal vein; MPV, main portal vein; RPV, right portal vein; UPJ, umbilical-portal junction; UV, umbilical vein.

Subsequent hemodynamic assessment provided crucial details. Rather than complete anatomical agenesis, the imaging demonstrated severe stenosis at the umbilical-portal junction (UPJ), causing near occlusion. Optimized color Doppler revealed a thread-like residual flow with focal aliasing traversing the stricture (Figure 1B). Notably, proximal to the stenosis, the intra-abdominal umbilical vein (UV) exhibited marked tortuous dilatation resembling cavernous transformation (diameter: 11.2 mm in Fetus B vs. 5.5 mm in Fetus A), indicative of high venous pressure secondary to downstream obstruction. This dilatation drained into a complex collateral network, which, according to the Achiron classification (1), was classified as an umbilical-systemic shunt (USS). The primary shunt diverted blood directly into the left common iliac vein (Figure 1C), while additional collateral flow, observed along the thoraco-abdominal wall, directed blood toward the right atrium (Figure 1D). The shunt likely caused volume overload, evidenced by significant inferior vena cava (IVC) dilatation (5.5 mm in Fetus B vs. 3.5 mm in Fetus A) (Figure 1E).

Such findings suggested a classic hemodynamic steal phenomenon, in which the low-resistance systemic pathway compromised intrahepatic perfusion. Consequently, the hepatic artery (HA) exhibited compensatory dilatation (1.6 mm in Fetus B vs. 0.8 mm in Fetus A), consistent with the hepatic arterial buffer response (HABR) (Figure 1F). Prompted by these quantitative findings, we refined the diagnosis to USS secondary to critical stenosis and opted for expectant management.

The longitudinal hemodynamic evolution is summarized in Table 1. By 32 weeks of gestation, progressive expansion of the stenotic segment was observed. However, persistent aliasing on color Doppler indicated residual narrowing rather than complete normalization. This was confirmed by quantitative assessment, with Fetus B exhibiting significantly elevated peak systolic velocity (PSV) compared to the control Fetus A (55.2 vs. 22.3 cm/s). Simultaneously, the systemic shunt spontaneously diminished, and intrahepatic portal perfusion was clearly reconstituted (Figure 2A,2B). By 34 weeks of gestation, color Doppler imaging confirmed the near-normal restoration of the PVS (Figure 2C,2D). Postnatal ultrasound at 3 months confirmed a structurally normal liver and a patent PVS with physiological hepatopetal flow (Figure 2E,2F). The infant corresponding to Fetus B showed appropriate catch-up growth and normal liver function, supporting the transient and self-limiting nature of the prenatal hemodynamic alterations.

Figure 2 Follow-up hemodynamic assessment at 32 and 34 weeks of gestation, and postnatal evaluation. (A) Color Doppler imaging at 32 weeks of gestation showed recanalization of the UPJ. Although flow volume had increased, the persistence of mosaic flow signals (aliasing) indicated residual stenosis (arrow). (B) The MPV, LPV, and RPV showed visible flow signals, indicating restoration of intrahepatic perfusion. (C,D) Color Doppler imaging at 34 weeks of gestation revealed near-normal restoration of the PVS, displaying physiological flow in the LPV (C), and the MPV and RPV (D). (E,F) Postnatal ultrasound at 3 months confirmed a patent PVS with physiological hepatopetal flow in the MPV (E) and LPV (F). DV, ductus venosus; GB, gallbladder; LPV, left portal vein; MPV, main portal vein; PVS, portal venous system; RPV, right portal vein; UPJ, umbilical-portal junction; UV, umbilical vein.

All procedures in this case were performed in accordance with the ethical standards of the institutional and/or national research committee(s), and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patient for the publication of this case description and the accompanying images. A copy of the written consent form is available for review by the editorial office of this journal.

Discussion

The hemodynamic evolution observed in this case illustrates a distinct pathophysiological cascade characterizing a state of functional occlusion. Unlike true anatomical PVA, where the vessel is embryologically absent (2,3), this case shows that critical stenosis at the UPJ can create a high-resistance barrier. This barrier effectively diminishes downstream portal flow to velocities undetectable by routine ultrasound examination, creating a hemodynamic masking effect (4). This phenomenon explains the initial diagnostic pitfall: the portal vein was physically present but hemodynamically dormant, mimicking the “silent” portal system typically seen in total agenesis.

A key finding was the complex mechanism of the systemic shunt and its subsequent resolution. The critical stenosis forced the high-pressure umbilical venous return to seek a low-resistance escape pathway. This manifested proximal to the stenosis as marked tortuous dilatation of the UV—resembling cavernous transformation—and the formation of a massive USS draining into the iliac vein (5,6). Additionally, the recruitment of superficial collaterals on the thoraco-abdominal wall (Figure 1D) further corroborated the presence of severe venous outflow obstruction (7). These alterations resulted in a classic hemodynamic steal phenomenon, compromising intrahepatic perfusion (8).

This compromise in hepatic perfusion was likely a contributing factor to the fetal growth restriction (FGR) observed at 30 weeks of gestation. The fetal liver is the primary site for the production of insulin-like growth factor 1 (IGF-1), a crucial mediator of fetal somatic growth (9,10). Previous studies on congenital portosystemic shunts have postulated that prolonged bypass of the liver prevents trophic factors in the umbilical blood from reaching hepatocytes, thereby downregulating IGF-1 synthesis (11,12). In our case, the timing of FGR coincided with the peak of shunting and IVC dilatation (Table 1), supporting the hypothesis that the steal effect was hemodynamically significant enough to affect fetal growth potential (13).

Notably, this case highlights the specific role of quantitative ultrasound in differentiating between anatomical and functional agenesis. The HABR, evidenced in this case by significant compensatory dilatation of the HA (1.6 mm at 23 weeks), is a highly sensitive marker for reduced portal flow (14,15). However, HABR is non-specific; it occurs in both complete agenesis and severe stenosis (16). Therefore, HABR alone cannot confirm agenesis. A key differential marker emerged during longitudinal surveillance: the detection of a high-velocity jet (PSV >55 cm/s) at the stricture site. This stenotic jet is a characteristic sign of a patent but narrowed vessel, effectively ruling out anatomical agenesis (17).

The spontaneous resolution observed from 32 weeks of gestation onwards is consistent with fluid dynamics principles. Spontaneous closure or regression of fetal venous shunts has been documented (18,19). In this case, as Fetus B grew, the stenotic segment likely underwent expansive remodeling or maturation, aided by increased hydrostatic driving pressure, reducing the resistance at the UPJ. As vascular resistance in the portal pathway normalized, the pressure gradient driving the systemic shunt diminished, allowing the preferential restoration of physiological hepatopetal flow and the functional closure of collateral pathways (20).

In summary, severe umbilical-portal stenosis can mimic PVA by suppressing flow signals and inducing compensatory systemic shunts. We propose a two-step diagnostic strategy: (I) comprehensive mapping: in cases of non-visualized portal veins, sonographers should apply standardized scanning techniques, such as the “five-plane method” (21), to achieve better visualization of the hepatic flow and meticulously interrogate for residual flow or aliasing at the UPJ, while quantifying HA hemodynamics; and (II) longitudinal surveillance: as demonstrated by the spontaneous recanalization and catch-up growth in this case, hemodynamic anomalies can be transient. This is further supported by postnatal studies demonstrating that even in patients prenatally diagnosed with portal agenesis, the intrahepatic portal system can often be visualized using angiography with a shunt occlusion test (22). Caution is therefore warranted to avoid premature pregnancy termination in cases of “pseudo-agenesis”, where expectant management may lead to a favorable postnatal outcome.

Acknowledgments

None.

Footnote

Funding: This work was supported by a grant from the Department of Science and Technology of Sichuan Province (No. 2025ZNSFSC0345).

Conflicts of Interest: Both authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-2026-1-0117/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this case were in accordance with the ethical standards of the institutional and/or national research committee(s), and with the Helsinki Declaration and its subsequent amendments. Written informed consent was obtained from the patient for publication of this case description and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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