Anatomical Variations of Portal Venous System: Importance in Surgical Clinic

Abstract

- BACKGROUND: Knowledge of the portal system and its anatomical variations aids to prevent surgical adverse events. The portal vein is usually made by the confluence of the superior mesenteric and splenic veins, together with their main tributaries, the inferior mesenteric, left gastric, and pancreaticoduodenal veins; however, anatomical variations are frequent. AIM: This article presents a literature review regarding previously described anatomical variations of the portal venous system and their frequency. METHODS: A systematic review of primary studies was performed in the databases PubMed, SciELO, BIREME, LILACS, Embase, ScienceDirect, and Scopus. Databases were searched for the following key terms: Anatomy, Portal vein, Mesenteric vein, Formation, Variation, Variant anatomic, Splenomesenteric vein, Splenic vein tributaries, and Confluence. RESULTS: We identified 12 variants of the portal venous bed, representing different unions of the splenic vein, superior mesenteric vein, and inferior mesenteric vein. Thomson classification of the end of 19th century refers to the three most frequent variants, with type I as predominant (M=47%), followed by type III (M=27.8%) and type II (M=18.6%). CONCLUSION: Thomson classification of variants is the most well-known, accounting for over 90% of portal venous variant found in clinical practice, inasmuch as the sum of the three junctions are found in over 93% of the patients. Even though rarer and accounting for less than 7% of variants, the other nine reported variations will occasionally be found during many abdominal operations.

A Rare Variant of the Portal Vein Formation

“…Figure 2 shows a diagram of the described variation. The SV receives splenic tributaries, the left gastroepiploic vein, short gastric veins, posterior gastric veins, pancreaticoduodenal veins, and IMV (2,3,6). SMV receives tributaries from the small intestine (jejunal and ileal), colon (ileocolic, right colic, and middle colic (MCV)), pancreas, and stomach through the right gastroepiploic veins (3,6).…”

“…The SV receives splenic tributaries, the left gastroepiploic vein, short gastric veins, posterior gastric veins, pancreaticoduodenal veins, and IMV (2,3,6). SMV receives tributaries from the small intestine (jejunal and ileal), colon (ileocolic, right colic, and middle colic (MCV)), pancreas, and stomach through the right gastroepiploic veins (3,6). The MCV typically joins the SMV on its anterior surface when the SMV crosses the uncinate process of the pancreas (8).…”

“…The Thomson classification (1890) of PV variants is the most well-known in surgical and radiological practice (3,4). Prado Neto and Petroianu in their systematic review describe 12 variants of PV formation out of which the first three variants are the most frequent and found in around 93% of the patients and were first described by Thomson (3).…”

“…In type XI, LGV and IMV drain into SMV. In XII, there are 2 IMVs, each draining into SMV and SV (3,5). The MCV typically drains the proximal 2/3 of the transverse colon, accompanying the middle colic artery, and drains into the SMV in around 80% of cases (6,15,16).…”

“…Here, the PV runs between the two layers of lesser omentum at its free edge and can be compressed manually during surgeries. It enters the liver at the porta hepatis (2,3). Knowledge regarding its variants is important in interpreting radiological images and surgical procedures to prevent adverse events.…”