Portal vein aneurysm mimicking a pancreatic mass: A case report with an emphasis on imaging pitfalls

Abstract

Portal vein aneurysm (PVA) is a rare vascular abnormality that may mimic pancreatic or peri-pancreatic masses. We report a case of a woman in her 50s who was referred to our hospital after an annual routine medical check-up revealed a suspected pancreatic cyst. Initial non-contrast MRI and multiphase contrast-enhanced CT demonstrated a round enhancing lesion adjacent to the portal venous confluence, raising suspicion for a hypervascular pancreatic tumor. Subsequent endoscopic ultrasonography with Doppler confirmed turbulent venous flow within the lesion, consistent with a portal vein aneurysm. The lesion gradually regressed during follow-up. This case highlights the importance of including vascular lesions in the differential diagnosis of pancreatic masses and demonstrates the diagnostic role of Doppler-enhanced ultrasonography and multiphase CT.

Introduction

Portal vein aneurysm (PVA) is a rare vascular entity increasingly recognized due to advances in cross-sectional imaging [1,2]. Although its relation to portal hypertension has been emphasized, some patients with PVAs are asymptomatic and have no signs suggestive of portal hypertension; the lesion can be incidentally detected by ultrasonography (US) [3]. PVAs can be either fusiform or saccular. In the liver, saccular PVAs on B-mode US images, if care is not taken, can be easily mistaken for much more common liver cysts, as both of these lesions appear well-demarcated with anechoic content [4].

Similar pitfalls may be encountered in PVAs occurring in other locations. We present a case of a PVA initially suspected to be a pancreatic cyst, highlighting the importance of multimodality imaging and endoscopic ultrasonography (EUS) in diagnosis, and discussing management strategies.

Case presentation

Patient information

A woman in her 50s was referred to our hospital after an annual routine medical check-up revealed a suspected pancreatic cyst on routine B-mode US. No Doppler US was performed at the referring hospital because it was a usual screening examination. She had no symptoms. Medical history was unremarkable except for an appendectomy at age 42. She had no allergies and no smoking or alcohol history. Menopause occurred at age 52.

Laboratory tests on referral showed mild elevation of liver enzymes (AST 31 U/L, ALT 46 U/L), while alkaline phosphatase, bilirubin, and γ-GTP levels were within the normal range (ALP 100 U/L, bilirubin 0.5 mg/dL, γ-GTP 32 U/L). Tumor markers were unremarkable, with CA19-9 < 2 U/mL and CEA 2.7 ng/mL.

Diagnostic assessment

MRI

First, non-contrast MRI was performed, reflecting a provisional diagnosis of pancreatic cyst made at the referring hospital. Consistent with the tentative diagnosis, a 25-mm well-demarcated, unilocular-cyst-like lesion was identified in the pancreatic head (Fig. 1). The lesion demonstrated high signal on T2-weighted imaging, low signal on T1-weighted imaging, no fat content, and facilitated diffusion on diffusion-weighted imaging/ADC map. The signal intensity was homogeneous across sequences. Her liver appeared normal with no signs of portal hypertension. Differential diagnoses included pancreatic retention cyst, post-pancreatitis pseudocyst, solid pseudopapillary neoplasm, and serous cystic neoplasm.

Fig. 1.

Abdominal MRI findings. (A) Axial T2-weighted image shows a 25-mm, well-demarcated lesion located in the pancreatic head (arrow), with homogeneous high signal. (B) The corresponding T1-weighted image shows low signal, and (C and D) diffusion-weighted imaging demonstrates facilitated diffusion. These findings seem consistent with a pancreatic cyst or cystic neoplasm.

CT

After the MRI examination, dynamic contrast-enhanced CT was performed. A 28- mm hypervascular lesion was noted at the same location as on MRI (Fig. 2). On non-contrast images, the lesion showed attenuation similar to that of the pancreatic parenchyma, which was inconsistent with the cystic appearance on MRI. On the arterial phase, the lesion demonstrated strong enhancement, raising a suspicion for a solid hypervascular tumor. On the portal venous phase, the lesion maintained marked enhancement nearly equivalent to that of large vessels such as the aorta and the portal vein. It was close to the main pancreatic duct, common bile duct, and superior mesenteric vein, but without apparent invasion. Based on the CT findings, pancreatic cyst and neoplasms with a predominant cyst became less likely, and then, the differential diagnoses included pancreatic neuroendocrine tumor, solid-type serous cystic neoplasm, paraganglioma, hemangioma, solitary fibrous tumor, and hypervascular metastasis.

Fig. 2.

Dynamic CT findings. Precontrast (A) and arterial-phase (B) images show a 28-mm hypervascular lesion within or adjacent to the pancreatic head (arrow). The lesion shows strong enhancement comparable to the renal cortex on the arterial phase (B) and maintains marked enhancement on the portal venous phase axial (C) and coronal reformatted (D) images. (E) A drawing illustrates the anatomic relationship between the lesion (its final diagnosis is a PVA) and adjacent vessels. No invasion of adjacent ducts or vessels is noted. Abbreviations: *, the lesion; PT, main portal trunk; SMV, superior mesenteric vein; SV, splenic vein.

EUS

After MRI and CT, EUS was performed and revealed a 25-mm round lesion adjacent to the superior mesenteric vein at the spleno-portal confluence (Fig. 3). The lesion had a smooth inner wall, and Doppler imaging demonstrated turbulent flow with continuity from the main portal vein. Under perfluorobutane contrast-enhanced-EUS, the lesion showed enhancement identical to the main portal vein, clearly showing the continuity of the portal vein and the lesion. These findings confirmed the diagnosis of a portal vein aneurysm.

Fig. 3.

Endoscopic ultrasonography (EUS) findings. (A) EUS shows a 25-mm round lesion adjacent to the superior mesenteric vein at the spleno-portal confluence. (B) Doppler imaging shows turbulent flow within the lesion, continuous with the main portal vein (★). (C) Perflubutane-enhanced EUS shows enhancement identical to the main portal vein, confirming its vascular nature.

Management and outcomes

Conservative follow-up was adopted. A CT scan 1 year later showed shrinkage of the aneurysm, leaving only a 4 mm protrusion in the portal vein (Fig. 4). A 2-year follow-up CT demonstrated stable findings. The patient remains asymptomatic; annual surveillance continues.

Fig. 4.

Follow-up CT findings. At 1-year post-diagnosis, CT shows shrinkage with a 4-mm protrusion of the portal vein wall (arrow) in axial (A) and coronal reformatted (B) images. Two years later, the finding remains unchanged.

Discussion

Portal vein aneurysm is a rare vascular anomaly with an estimated prevalence of 0.6 per 1,000 persons [2]. The most common locations for PVAs are the main portal trunk and the portal bifurcation/intra-hepatic, followed by the spleno-mesenteric confluence [5]. If a PVA occurs in the spleno-portal confluence, because of its proximity to the pancreatic head, it can mimic a pancreatic tumor when imaging demonstrates arterial enhancement or saccular morphology. Although PVAs are often associated with portal hypertension or portal thrombus [3,5], this patient has no signs of portal hypertension on CT or MRI, possibly contributing to misinterpretation as a hypervascular pancreatic tumor. Similar diagnostic challenges sometimes happen in other organs as well; for instance, it is known that an internal carotid artery aneurysm can mimic a pituitary tumor on imaging [6].

This case highlights one important clinical lesson: when evaluating a pancreatic or peri-pancreatic mass, vascular etiologies—including aneurysms—should be considered. Failure to include vascular lesions in the differential diagnosis may lead to unnecessary biopsy or even surgery. Doppler US and multiphase CT play a pivotal role in distinguishing a PVA from cyst or solid tumors [[1], [2], [3],7]. Although arterial-phase enhancement may be misleading, demonstration of continuity with the portal venous system and identical enhancement during the portal venous phase strongly suggests a vascular lesion.

MRI can provide additional evaluation of internal morphology and soft-tissue signal characteristics, but may be confusing when cyst-like appearances, as in this case, are shown across many MRI sequences. In addition, typical flow voids were not detected in the aneurysm but were seen in the main portal vein. This discrepancy in imaging may have misled us to the initial diagnosis of a distinct lesion adjacent to the portal vein.

EUS with Doppler is valuable for confirming turbulent venous flow and direct communication with the portal venous system. In this case, fluoroscopic Doppler confirmation helped avoid unnecessary invasive procedures and clarified the diagnosis.

Management depends on symptoms, size, and complications. Surgical indication is considered for complicated PVAs, including those with rupture, thrombosis, symptomatic aneurysms, or in enlarging aneurysms due to risk of spontaneous rupture [5]. Most asymptomatic cases, including this one, can be managed conservatively. Notably, rare reports describe spontaneous regression of PVA, consistent with this case [8].

Conclusion

Portal vein aneurysm should be included in the differential diagnosis when evaluating hypervascular pancreatic lesions, particularly when adjacent to the venous confluence. Knowledge of the imaging pitfalls and the appropriate use of multiphase CT and Doppler ultrasonography would prevent misinterpretation.

Ethics statement

Ethics approval was waived by our institutional review board because this is a single anonymized case report.

Declaration of Generative AI and AI-assisted technologies in the writing process

During the preparation of this work, the author used ChatGPT (OpenAI) to improve the clarity of the English language and formatting. After using this tool, the author reviewed and edited the content as needed and takes full responsibility for the content of the publication.

Patient consent

Written informed consent was obtained from the patient for the publication of this case report and accompanying images.