Ultrasound liver segments are the same eight Couinaud units, read with a transducer instead of a gantry. The map is functional — each segment has its own portal inflow, hepatic-vein outflow, and bile duct — so a segmentectomy can take one “district” and leave the rest. This page is that map on US. It is not a CT rename.
If you meant the same map on CT → CT liver segments. If you meant a CT organ mask → liver segmentation on CT.
The Couinaud city, on US
Hepatic veins are the highways. Portal branches are the local streets. Numbering runs clockwise from the caudate (I) at the back. The gallbladder sits between IVb and V — the landmark you actually use on a subcostal sweep.
| Segment | Lobe | Location | US landmarks |
|---|---|---|---|
| I | Caudate | Most posterior | Posterior to the portal vein |
| II | Left | Superior-lateral | Left hepatic vein |
| III | Left | Inferior-lateral | Left portal-vein branches |
| IVa | Left | Superior-medial | Middle hepatic vein, left side |
| IVb | Left | Inferior-medial | Gallbladder fossa |
| V | Right | Inferior-anterior | Anterior branch of the right portal vein |
| VI | Right | Inferior-posterior | Posterior branch of the right portal vein |
| VII | Right | Superior-posterior | Right hepatic vein |
| VIII | Right | Superior-anterior | Middle hepatic vein, right side |
IVa vs IVb is the US-specific split. On a routine axial CT, segment 4 is often one row. Here the gallbladder fossa is how you tell them apart.
Playboy Bunny and Color Doppler
In a high transverse / slightly oblique view the three hepatic veins (right, middle, left) meet the IVC as a pair of ears plus a head — the Playboy Bunny sign. That single frame orients you on the superior segments: VII and VIII on the right of the middle vein, IVa and II on the left. Miss the bunny and you are guessing which “ear” is middle vs left.
Color Doppler is the road sign, not a decoration. Portal flow and hepatic-vein flow run different directions; Doppler tells you which vessel you landed on when grayscale is a grey blob. Without it, a replaced right hepatic artery or a fat-filled fissure will steal a segment from you. Direction and velocity are how you confirm the border, then you put the lesion on the correct side.
Planes: subcostal transverse for the bunny and the portal bifurcation; intercostal for VII/VIII when the rib is in the way; a sagittal sweep down the left lobe for II vs III. Each press of the probe is a 2D slice. The 3D map is in the sonographer’s head. Obesity, gas, and cirrhosis (twisted veins, no plane) are why this stays a skill.
Why the segment number matters
- Segmentectomy. Tumor in VI only → take VI. That is the point of Couinaud.
- Guided biopsy. VII and VIII are the awkward high-right segments; the path has to miss the big veins. Segment of the sample is a known complication factor.
- Ablation / chemoembolization. Aim at a segment, spare the rest.
- Cirrhosis follow-up. Segments do not shrink equally. Volume change on US is a clue, not a CT remnant calculation.
AI that auto-outlines US segments is a research line. It does not replace the bunny or Doppler on this page. Generic deep-learning segmentation (any organ, any modality) is medical image segmentation.
PYCAD builds the viewers clinicians use to hang a Couinaud map next to the clip. Case studies.