Diagnostic ultrasound ( PDFDrive )

76 PART II Abdominal and Pelvic Sonography
CL
CL
A
B
FIG. 4.3 Caudate Lobe. (A) Sagittal view and (B) transverse view show the caudate lobe (CL) separated from the left lobe by the issure for
the ligamentum venosum (arrows) anteriorly. Posterior is the inferior vena cava.
lobar issure and separates the anterior segment of the right lobe
from the medial segment of the let. he right hepatic vein runs
within the right intersegmental issure and divides the right lobe
into anterior and posterior segments. In more caudal sections
of the liver, the right hepatic vein is no longer identiied; therefore
the segmental boundary becomes a poorly deined division
between the anterior and posterior branches of the right portal
vein. he major branches of the right and let portal veins run
centrally within the segments (intrasegmental), with the exception
of the ascending portion of the let portal vein, which runs
in the let intersegmental issure. he let intersegmental issure,
which separates the medial segment of the let lobe from the
lateral segment, can be divided into cranial, middle, and caudal
sections. he let hepatic vein forms the boundary of the cranial
third, the ascending branch of the let portal vein represents the
middle third, and the issure for the ligamentum teres acts as
the most caudal division of the let lobe (Table 4.1). 2
FIG. 4.4 Hepatic Venous Anatomy. The three hepatic veins—right
(RHV), middle (MHV), and left (LHV)—are interlobar and intersegmental,
separating the lobes and segments. At the level of the hepatic venous
conluence with the inferior vena cava, the right hepatic vein separates
the right posterior segment (segment 7) from the right anterior segment
(segment 8). The left hepatic vein separates the left medial segment
from the left lateral segment. The middle hepatic vein separates the
right and left lobes. As shown here, the hepatic veins are best seen on
a subcostal oblique view.
lobe, which may appear separate from the liver and mimic
lymphadenopathy.
Understanding the vascular anatomy of the liver is essential
to an appreciation of the relative positions of the hepatic segments.
he major hepatic veins course between the lobes and segments
(interlobar and intersegmental). hey are ideal segmental
boundaries but are visualized only when scanning the superior
liver (Fig. 4.4). he middle hepatic vein courses within the main
Couinaud Anatomy
Because sonography allows evaluation of liver anatomy in multiple
planes, lesions can be localized to speciic segments. his can
aid surgical planning and follow-up of lesions over time. Couinaud
anatomy is now the universal nomenclature for hepatic
lesion localization (Table 4.2). 3 his description is based on portal
segments and is of both functional and pathologic importance.
Each segment has its own blood supply (arterial, portal venous,
and hepatic venous), lymphatics, and biliary drainage. hus the
surgeon may resect a segment of a hepatic lobe, providing the
vascular supply to the remaining lobe is let intact. Each segment
has a branch or branches of the portal vein at its center, bounded
by a hepatic vein. here are eight segments. he right, middle,
and let hepatic veins divide the liver longitudinally into four
sections. Each of these sections is further divided transversely
by an imaginary plane through the right main and let main
portal pedicles. Segment I is the caudate lobe, segments II and
III are the let superior and inferior lateral segments, respectively,
and segment IV, which is further divided into IVa and IVb, is