Streamline Flow of the Portal Vein Affects the Distribution of Colorectal Cancer Metastases: Clinical Reality or Just a Belief? A Systematic Review and Meta-Analysis.

The "streamline flow" of the portal vein (PV) is a controversial yet well-known theory presented almost 125 years ago. It states that blood from the superior mesenteric vein (SMV) goes preferentially to the right liver lobe, while splenic and inferior mesenteric veins divert blood predominantly to the left lobe, affecting this way the metastatic distribution of colorectal cancer (CRC). The aim of this systematic review is to assess its validity by examining and combining all the relevant literature with a critical eye. This study constitutes a systematic review of the literature and adheres to all PRISMA system criteria. Three search engines (PubMed, Google Scholar, and the Cochrane Library) were used, and 11 out of 435 studies between 1984 and 2024 were finally included in this meta-analysis. All statistical analysis was conducted using RevMan Web, Version: 7.12.0, and Jamovi v 2.3.260 software. The meta-analysis revealed that regardless of the primary location of the tumor, the metastases preferentially migrate to the right lobe due to various possible reasons. The prevalence of metastases from right colon cancer to the right liver lobe was 75%, while the prevalence of left colon cancer metastases to the right lobe was 68%. This difference was not found statistically significant. The theory has been proven inaccurate, at least from the perspective of the origin-associated distribution of CRC metastases in the liver lobes, and therefore bears no clear predictive value. Further research under different perspectives is essential for determining more definite conclusions.