Upper limit of normal portal vein diameter

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Understanding how the portal vein size reflects portal pressure is key. In a healthy adult, the main portal vein diameter is normally up to about 13 mm. When you measure, you do it inner-to-inner at the main portal vein near the porta hepatis, ideally with minimal respiratory variation.

So 13 mm represents the upper limit of normal. A diameter around this size suggests normal portal flow, while enlargements beyond this point raise concern for portal hypertension, with larger values indicating greater likelihood of abnormal pressure. A 10 mm measurement is still normal but not at the upper limit; 15 mm and especially 20 mm are progressively more abnormal and would prompt further evaluation for portal hypertension or other vascular issues.