Circumportal pancreas: a review of the literature and image findings

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Executive Summary

Circumportal pancreas (CP) is a rare congenital anomaly characterized by the encasement of the portal vein (PV) and/or superior mesenteric vein (SMV) by fused pancreatic tissue. While commonly found in swine, it is present in only 1–3.4% of the human population and is typically asymptomatic, often discovered incidentally during abdominal imaging.

The primary clinical significance of CP lies in its impact on pancreatic surgery. Preoperative identification is critical to avoid major complications, most notably pancreatic fistulas, which occur in approximately 38.5% of reported surgical cases. CP is also frequently associated with vascular variants, such as replaced hepatic arteries, which can complicate oncologic resections and vascular reconstructions. Advanced imaging (CT and MRI) is the gold standard for diagnosis, allowing surgeons to classify the anomaly based on the location of the pancreatic duct and the site of fusion relative to the splenic vein.

Overview and Pathophysiology

Circumportal pancreas occurs when the uncinate process of the pancreas hypertrophies and fuses with the dorsal portion of the pancreas behind the mesenteric vessels, above the spleno-portal junction.

  • Embryogenesis: The anomaly is believed to arise during the 7th week of fetogenesis due to variations in the normal rotation and high fusion of the ventral and dorsal pancreatic precursors.

  • Terminology: The condition is also referred to as "portal annular pancreas." To avoid confusion with "annular pancreas"—which encircles the duodenum—the term "circumportal pancreas" is preferred when the PV or SMV is involved.

Classification Systems

CP is classified based on the relationship between the pancreatic tissue, the main pancreatic duct (MPD), and the surrounding vasculature.

Level of Fusion and Morphology

Studies by Karasaki and Joseph established classifications based on the site of fusion relative to the splenic vein and the course of the duct.

Classification Type

Description

Suprasplenic

Fusion occurs above the level of the splenic vein.

Infrasplenic

Fusion occurs below the level of the splenic vein.

Mixed

Fusion involves both suprasplenic and infrasplenic regions.

Type I

Ventral and dorsal buds fuse posterior to the PV with a retroportal duct.

Type II

Type I findings accompanied by pancreas divisum.

Type III

Only involves the uncinate process; the duct is anterior to the PV (anteportal).

Tappouni Five-Grade Classification

A comprehensive system combines the fusion location with the course of the main pancreatic duct:

  1. Grade 1: Normal anatomy.

  2. Grade 2: Anteportal suprasplenic.

  3. Grade 3: Retroportal suprasplenic.

  4. Grade 4: Anteportal infrasplenic.

  5. Grade 5: Retroportal infrasplenic.

In a series of 40 cases, the most common variant was anteportal suprasplenic (82%).

Clinical and Surgical Implications

The presence of CP significantly alters the risk profile and technical requirements of pancreatic resections, such as pancreaticoduodenectomy or distal pancreatectomy.

Risk of Postoperative Fistula

Pancreatic fistula is the most common adverse outcome, occurring when the division of the pancreatic neck creates two distinct cut surfaces—one above the portal vein and one below it—both of which may source a leak.

  • Statistical Incidence: Of 13 documented surgical outcomes, 5 patients (38.5%) developed a fistula.

  • Mitigation Strategies: Techniques to reduce fistula risk include additional resection of the pancreatic body distal to the original line to create a single cut surface, or specialized suturing to narrow the pancreatic surface.

Associated Vascular Variants

Vascular anomalies are found in approximately 30% of CP cases. These must be identified preoperatively to plan for vascular reconstruction during oncologic resections:

  • Intraparenchymal Arteries: The common hepatic artery (CHA) or replaced right hepatic artery (RHA) may run directly through the pancreatic head (noted in 22.5% of one series).

  • Replaced Arteries: Replaced RHA from the superior mesenteric artery (SMA) or replaced left hepatic artery (LHA) from the left gastric artery (LGA).

Diagnostic Challenges and Misidentification

If not identified preoperatively, CP can lead to:

  • Inappropriate Reconstruction: Misidentifying the minor duct as the main duct during pancreaticojejunostomy.

  • Mistaken Tumor Extension: Pancreatic tissue encasing the vein may be misidentified as cancerous infiltration.

  • Unnecessary Surgery: In one reported case, a retention cyst within a CP was mistaken for a recurring neoplasm, leading to a secondary operative intervention.

Radiographic Identification

Since CP is asymptomatic, it must be actively sought during preoperative imaging.

  • Imaging Modalities: Multidetector-row CT and MRI/MRCP are the primary tools. MRCP is particularly useful for visualizing the relationship between the main pancreatic duct and the portal vein.

  • Radiographic Hallmark: The definitive sign is a continuity of tissue with pancreatic density located dorsal to the SMV or PV, resulting in complete encirclement of the vessel.

  • Differential Diagnosis: CP must be distinguished from peripancreatic lymphadenopathy or an extension of the caudate lobe of the liver.

Summary of Literature Findings (1987–2014)

A review of 91 cases identified in the literature provides the following data points:

  • Gender and Diagnosis: In some series, a majority of cases were found in women, with primary diagnoses ranging from colonic adenocarcinoma to hepatoma.

  • Vessel Involvement: Cases involved the PV (17), the SMV (3), or both (2).

  • Surgical Context: Of the 14 cases undergoing surgery, 11 were for suspected carcinoma and 3 for benign neoplasms (e.g., insulinomas, inflammatory masses).

  • Incidence Trends: The number of reported cases has increased over time, likely due to the increased use and resolution of modern imaging. However, because it is asymptomatic, the true incidence is likely higher than currently reported.