Claude Couinaud (1957) showed the liver is not two anatomical lobes but eight independently perfused segments (I-VIII), each fed by its own portal pedicle — a branch of the portal vein, hepatic artery and bile duct that travel together — and drained by one of three hepatic veins into the inferior vena cava.
Portal territories (inflow):
Right portal vein -> V, VI, VII, VIII
Left portal vein -> II, III, IV
(Segment I / caudate is perfused by both)
Hepatic venous drainage (outflow):
Right hepatic vein -> VI, VII
Middle hepatic vein -> IV, V, VIII
Left hepatic vein -> II, III
Segment I drains directly into the IVC via short
accessory veins — independent of all three main veins.
Because each segment has its own vascular pedicle, a surgeon can remove whole segments along the plane between two portal territories without starving or congesting the segments left behind — this is what makes anatomical (segment-based) liver resection possible, unlike an arbitrary wedge cut.
The key planning number is the Future Liver Remnant (FLR): the percentage of total liver volume left after resection. FLR = 100% − (sum of resected segment volumes as % of total). Below roughly 25-30% remnant in a healthy liver (higher, ~40%, if the liver is cirrhotic or chemotherapy-damaged) the remaining tissue cannot regenerate fast enough to meet metabolic demand, risking post-hepatectomy liver failure — so the resected/remnant split, not just tumor clearance, drives the operative plan.
- Resection plan — loads a standard named resection (right/left hepatectomy, extended right trisectionectomy, left lateral sectionectomy) by selecting the correct set of segments.
- Segment buttons / clicking the diagram — toggle any individual segment I-VIII on/off to build a custom resection and see its FLR immediately.
- Explode slider — pulls the eight segments apart from the hilum so the segment boundaries and vascular pedicles are easier to see.
- Vascular tree toggle — shows/hides the portal vein (blue) and hepatic vein (violet) branches feeding and draining each segment.
This 2D companion renders the same eight segments, volume weights, portal/hepatic-vein territories and FLR formula as the 3D model, laid out as a coronal (front-view) schematic — left/right position matches the true left/right split, and top/bottom matches superior/inferior — so it works as a flat clinical diagram rather than a rotatable model.