Basic Abdominal Anatomy
Landmarks that organize the abdomen
The sonographic map of the abdomen rests on a few fixed relationships. The liver is divided into eight Couinaud segments by portal vein branches and drained by three hepatic veins. The middle hepatic vein runs in the main lobar fissure and separates the right and left lobes; the right hepatic vein divides the right lobe into anterior and posterior sectors; the left hepatic vein separates the left medial and lateral segments. The caudate lobe (segment I) lies between the IVC and the fissure for the ligamentum venosum and drains directly into the IVC. The gallbladder fossa and main lobar fissure are the classic landmarks for the gallbladder.
The portal triad-portal vein, hepatic artery, and common bile duct-travels in the hepatoduodenal ligament; the bile duct lies anterior and to the right of the portal vein, with the hepatic artery between them.
The pancreas is retroperitoneal: head within the duodenal C-loop, uncinate process posterior to the superior mesenteric vein, and body/tail coursing toward the splenic hilum. The spleen sits posterior to the stomach and lateral to the left kidney; the right kidney lies posterior to the liver, and the left kidney is posterolateral to the spleen.
Traps
Do not confuse the ligamentum teres (round ligament) with the fissure for the ligamentum venosum. Segment numbering follows portal, not hepatic, venous anatomy. Never call splenomegaly from a single view-measure in two planes.
Rule of thumb
A lesion lying between the middle and right hepatic veins on an axial image belongs to the right anterior sector (segments V/VIII).