Stepwise evaluation of liver sectors and liver segments by endoscopic ultrasound

Table 1 The sectors and the segments of liver

Four hepatic sectors	Eight hepatic segments
	Segment I - the caudate lobe
Left lateral sector	Segment II - posterosuperior
	Segment III - anteroinferior
Left medial sector	IVa - superior segment
	IVb - inferior segment
Right anterior sector	Segment V - inferior segment
	Segment VIII - superior segment
Right posterior sector	Segment VI - inferior segment
	Segment VII - superior segment

This table shows the relationship of hepatic sectors and hepatic segments. The four segments of left liver are: I (caudate); II (left lateral superior); III (left lateral inferior); and IV (left medial) [subdivided into superior (IVa) and inferior parts (IVb) by Bismuth]. The four segments of right liver are: V (right anteroinferior); VI (right posteroinferior); VII (right posterosuperior) and VIII (right anterosuperior). The caudate lobe is often called an independent segment.

Table 2 The home bases of imaging for liver segments

Home bases	Defining of segments
Hepatic veins	LHV separates II and III from IV (a and b)
	MHV separates IVa from VIII and IVb from V
	RHV separates V from VI and VIII from VII
Portal vein and its branches	Superior segments lie above and inferior segments lie below the transverse fissure
	The LPV supplies segments II to IV
	The RPV supplies segments V to VIII
IVC	IVC passes through the bare area of the liver and is related to superior segments in the upper part, segment I for most of its course, and with segment VI close to the lower most part above the right kidney
IVC suprahepatic part	A transverse plane defines the upper limit of superior segments (II, IV, VIII, and VII)
Ligamentum teres	Separates segment III from IVb
Ligamentum venosum	Separates I from IVa and II
Gallbladder	Neck lies close to segment V and fundus close to segment VI, from stomach IVb comes between the gallbladder and probe

IVC: Inferior vena cava; LHV: Left hepatic vein; MHV: Middle hepatic vein; RHV: Right hepatic vein; LPV: Left branch of the portal vein; RPV: Right branch of the portal vein.

Table 3 A difference in the segments of imaging from the three positions

Station	Comment	Segments visualized
Abdominal part of the esophagus and stomach	Probe in the esophagus lies close to the left lobe of the liver and in the stomach close to the visceral surface of the liver	Superior segments and caudate lobe are in direct contact with the lower end of esophagus All segments except segment VIII on the visceral surface of liver are in contact with the stomach
Duodenal bulb	Probe lies close to the hilum of the liver	Direct contact with segment I and right lobe liver segments Left side segments are seen through caudate lobe, caudate process, and IVC
Second part of duodenum.	Probe lies close to the hilum of the liver	Direct contact with segment I and right lobe liver segments Left side segments are seen through caudate lobe, caudate process, and IVC

IVC: Inferior vena cava.

Table 4 The structures from three positions from station 1

Clockwise rotation from an open position to left	Part of portal vein	Part of hepatic vein	Other home base structures	Main sector of liver visualized	Main segments of liver visualized	Figure number for segment
Open position to left	PII and PIII	LHV	Diaphragm and heart	Left medial closer to left lateral1	II, III, and IV	2A, 2B, 3A, 5A
Neutral position after approximately 60° to 75° clockwise rotation	Fisheye appearance of LPV	MHV	Left edge of transverse fissure attached to ligamentum venosum and ligamentum teres	Left medial closer to probe than right anterior	I and IV	3A, 5B
Open position to right after further approximately 60° to 75° clockwise rotation	RPV dividing into anterior and posterior branches	RHV	Right edge of transverse fissure, IVC, gallbladder, and caudate process	Right anterior closer to probe than right posterior	V, VI, VII, and VIII	3A, 7A 7C, 7D

¹When the scope is in maximum open position only the left lateral segment is seen. IVC: Inferior vena cava; LHV: Left hepatic vein; MHV: Middle hepatic vein; RHV: Right hepatic vein; LPV: Left branch of the portal vein; RPV: Right branch of the portal vein.

Table 5 The representation of liver segments

Home base structure	Comment	Figure No.
Hepatic veins	The main left hepatic vein drains the two lateral segments of the left lobe (segments II and III)	9D
	The middle vein drains segment IV and the anterior sector of the right lobe (segments V and VIII)	9B
	The right vein drains the remainder of the right lobe (segments VI and VII) and a variable portion of segments Vand VIII	9C
Hepatic vein tributaries	The higher tributary of LHV going towards the diaphragmatic and costal surface belongs to segment II	9D
	The higher tributary of MHV going towards the diaphragmatic and costal surface belongs to segment VIII	9B, 14C, 14D
	The higher tributary of RHV going towards the diaphragmatic and costal surface belongs to segment VII	15A, 15C
	The tributary of LHV going towards the liver hilum drains segment IVa	14B
	The tributary of MHV going towards the liver hilum drains segment IVb	14D
	The tributaries of RHV going towards the liver hilum drains segments Vand VIII	9C
Right and left branches of the portal vein	The right branch of the portal vein supplies the right liver (segments Vto VIII)	7A, 7B, 7C, 7D
	The left branch of the portal vein supplies the left liver (segments II to IV)	5A, 5B, 5C, 5D, 6A, 6B
	The caudate lobe receives direct branches from both the right and left branches	12C
Segmental branches of the portal vein	The extrahepatic part supplies segment I	11D
	The anterior branch of the RPV supplies segments Vand VIII	7C
	The posterior branch of the RPV supplies segments VI and VII	7D
Right kidney	Lies lateral to the infrahepatic part of the IVC	8A
Caudate lobe	Forms an important anatomical landmark	10A, 10B, 10D, 11A, 11B, 11C

IVC: Inferior vena cava; LHV: Left hepatic vein; MHV: Middle hepatic vein; RHV: Right hepatic vein; LPV: Left branch of the portal vein; RPV: Right branch of the portal vein.