MRCS PART A · APPLIED BASIC SCIENCES
Liver segments: supply, boundaries & surface landmarks
Two selected anatomy objectives with four linked SBAs. Identify the reference system before naming a territory. This conventional segment map is not an individual operative plan or a test of liver reserve.
2 topics · 4 original SBAs
1 · Which map are you using?
Your task: Separate external lobes, functional hemilivers and inflow/outflow landmarks.
Does the falciform ligament divide the functional hemilivers?
It marks an external right/left division, not the functional watershed. The conventional functional division follows the gallbladder-fossa–IVC plane associated with the middle hepatic vein: Rex–Cantlie's plane.
Is a surface line the whole internal boundary?
No. A line helps describe a plane through a volume; it does not supply every vessel's course.
What changes when the stem asks for surface anatomy?
Use its stated surface reference, rather than answering a functional-territory question that was not asked.
What belongs inside a segment's portal pedicle?
Portal venous and hepatic arterial branches accompany the biliary branch. Hepatic veins provide outflow and are not a substitute name for the portal venous branch.
Does 'portal triad' mean three blood vessels?
No. The bile duct is a conduit for bile, not another blood vessel. Separate structure, carried material and direction of flow.
Why are portal branches and major hepatic veins different landmarks?
Portal branches define supplied territories; major hepatic veins are conventional boundary landmarks. Inflow territory and venous drainage do not have identical maps.
Must a named segment have an exclusive main hepatic vein?
No. Adjacent territories can share hepatic venous drainage. A segment label cannot prove an exclusive outflow route or adequate remaining function.
2 · Locate the territory, then challenge the shortcut
Your task: Apply selected Couinaud groupings while recognising that real boundaries are not perfect geometric planes.
Where does segment IV belong functionally?
In the conventional left medial section. II and III form the left lateral section; II–IV together constitute the functional left hemiliver. A surface-based right/left description must not silently replace this classification.
What if a report says only 'left lobe'?
Clarify whether it means the external lobe or the functional hemiliver. A label without its reference system can mislead.
Which segments form the conventional right posterior section?
VI and VII; V and VIII form the right anterior section. Trace the supplying branch rather than assuming that a posterior location on one view establishes the entire territory.
What if the posterior portal branch arises directly from the main trunk?
Its different origin is a branching variant, not proof that its destination has changed. Follow the demonstrated branches to the supplied tissue.
Are the straight boundaries in a teaching map exact in every liver?
No. Human specimen work found irregular segment boundaries, including an oblique IVa/IVb relationship. A simplified model is useful for orientation, not proof of a patient's exact boundary.
Does uncertainty make the conventional classification useless?
No. Use it as a shared description and verify the actual connections when precision matters.
Can this lesson choose a resection margin or remnant?
No. Those decisions need individual imaging, disease assessment, function and specialist planning; they cannot be derived from a segment number alone.