Macroscopic structure and landmarks
The upper surface of the liver is dome-shaped, precisely matching the contours of the diaphragm. The sagittal fissure serves as the most important surface landmark. It contains the round ligament of the liver (ligamentum teres, which is an obliterated umbilical vein), located within the falciform ligament (ligamentum falciforme).
On the inferior (visceral) surface, the porta hepatis (porta hepatis or hilum) occupies a central position. The portal vein, hepatic artery, and common bile duct pass through this depression. Anterior to the porta is the fossa for the gallbladder, and to the left of it is the quadrate lobe. The caudate lobe is located posteriorly, separating the porta of the organ from the inferior vena cava (IVC). An interesting anatomical variant of normal is Riedel's lobe — an elongation of the tip of the right lobe below the costal margin, which can sometimes mimic pathological organomegaly.
Segmental architecture and microanatomy
The liver is traditionally divided into right and left halves by an internal craniocaudal plane, landmarks for which include the IVC groove, the middle hepatic vein, and the gallbladder fossa. Further division into 8 Couinaud segments (Couinaud segments) is based exclusively on vascular supply characteristics. The caudate lobe (Segment I) is particularly distinct: it has a fully autonomous blood supply from both the right and left branches and features independent venous drainage directly into the IVC.
At the microscopic level, the parenchyma consists of lobules. Each lobule contains a central draining vein and sinusoids. Portal tracts containing the portal triad are located at the periphery of the lobules. The cellular composition of the organ includes not only working cells — hepatocytes, but also stellate cells and Kupffer cells, which are macrophages of the reticuloendothelial system (RES).
Vascular anatomy variations
Blood flow in the liver is unique: during meals, mesenteric blood flow can double, significantly increasing blood inflow via the portal vein. At the same time, arterial anatomy exhibits high variability. Normally, the common hepatic artery originates from the celiac trunk and divides into right and left branches. However, variants are common:
- Replaced left hepatic artery (originating from the left gastric artery).
- Replaced right hepatic artery (originating from the superior mesenteric artery).
- Presence of accessory arteries.
Blood drains via the hepatic veins into the IVC. In 70% of people, there are three main veins, while in 30% of cases, accessory venous trunks are found. Knowledge of these features is critical when planning resection or transplantation.
Basics of diagnostic imaging
Imaging methods play a key role in evaluating the liver:
- Ultrasound: Normally, the parenchyma has a homogeneous echostructure, and its echogenicity is slightly higher than that of the cortical layer of the adjacent kidney. Doppler imaging of the hepatic veins demonstrates transient reverse blood flow during the right atrial systole ('A' wave).
- Computed tomography (CT): The X-ray attenuation of normal parenchyma is 54–60 HU. Multiphasic CT is used routinely. In the arterial phase, hepatic veins do not enhance (remain dark), whereas most solid lesions actively take up contrast. In the portal venous phase, the veins appear bright.
- Magnetic resonance imaging (MRI): Features maximum soft tissue contrast. On T2-weighted images, the signal from the spleen is normally higher than that from the liver. The Dixon method (Dixon) is widely used to assess steatosis — fat content is confirmed by a drop in signal intensity on opposed-phase images.
Briefly: answers to topical questions
What elements make up the microscopic portal triad of the liver?
The microscopic portal triad of the liver consists of three tubular structures surrounded by loose fibrous connective tissue.
- Branch of the hepatic artery (a. hepatica) — interlobular artery.
- Branch of the portal vein (v. portae) — interlobular vein.
- Bile duct (ductuli biliferi) — interlobular bile duct, which collects bile from the lobules.
These elements travel together within the interlobular connective tissue at the junctions of adjacent hepatic lobules.
Which ligaments form the anchoring apparatus of the liver?
According to sources, the ligaments and peritoneal reflections associated with the liver include:
- Round ligament of the liver (ligamentum teres) — located within the falciform ligament.
- Falciform ligament (ligamentum falciforme) — contains the round ligament of the liver; also borders the left anterior perihepatic space.
- Right coronary ligament (coronary ligament) — forms the right lateral border of the bare area of the liver.
- Ligamentum venosum (ligamentum venosum) — associated with the fissure for the ligamentum venosum between the caudate and left lobes.
- Hepatogastric ligament (gastrohepatic ligament) — extends from the lesser curvature of the stomach to the fissure for the ligamentum venosum.
- Hepatoduodenal ligament (hepatoduodenal ligament) — connects the superior duodenal flexure to the porta hepatis; contains the common hepatic duct, common bile duct, hepatic artery, and portal vein.
Which organs and anatomical structures are adjacent to the visceral surface of the spleen?
The following organs are adjacent to the visceral surface of the spleen (facies visceralis), forming corresponding impressions on it:
- Gastric fundus — contacts the spleen, forming the gastric impression (impressio gastrica).
- Upper pole of the left kidney and adrenal gland — form the renal impression (impressio renalis).
- Left colic flexure — contacts the organ, forming the colic impression (impressio colica).
- Tail of the pancreas — lies adjacent to the spleen, forming the pancreatic impression (impressio pancreatica).
Also located on this concave surface is the hilum of the spleen (hilum lienis), through which vessels and nerves pass.
The portal triad includes three elements easily remembered by the acronym VAP: Vein (portal), Artery (hepatic), and Bile duct.
Class and exam questions
What is Riedel's lobe and is it pathological?
Riedel's lobe is a normal anatomical variant of liver shape, representing an elongation of the tip of the right lobe anteriorly and inferiorly past the costal margin. It is neither a separate segment nor a sign of disease.
How to differentiate hepatic veins from portal vein branches on ultrasound?
Branches of the portal vein have prominent hyperechoic (bright) walls. In contrast, the walls of the hepatic veins are not visually distinct and blend with the surrounding parenchyma.
What is the anatomical uniqueness of the caudate lobe (segment I)?
It has a fully autonomous blood supply from both the left and right branches of the portal vein and hepatic artery, and its venous drainage occurs directly into the inferior vena cava, bypassing the major hepatic veins.
What else to study on this topic
- Multiphasic liver CT: interpretation of unenhanced, arterial, portal, and delayed phases
- Variants of hepatic artery anatomy (replaced and accessory branches)
- Liver MRI using the Dixon method: diagnosing steatosis
- Hepatobiliary and iron oxide-based contrast agents
- Radiological anatomy and diseases of the spleen (congenital and acquired)
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Other topics in the section "Diagnostic Radiology of the Abdominal Organs"
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