Diagnostic ultrasound ( PDFDrive )

80 PART II Abdominal and Pelvic Sonography
Diaphragm
Right triangular
ligament
Coronary
ligament
Falciform
ligament
Left triangular
ligament
Ligamentum teres (round ligament)
(obliterated umbilical vein)
FIG. 4.9 Hepatic Ligaments. Diagram of anterior surface of the liver.
border extends to or slightly below the costal margin. An accurate
assessment of liver size is diicult with real-time ultrasound
equipment because of the limited ield of view. Gosink and
Leymaster 7 proposed measuring the liver length in the midhepatic
line. In 75% of patients with a liver length of greater than 15.5 cm,
hepatomegaly is present. Niederau et al. 8 measured the liver in
a longitudinal and anteroposterior diameter in both the midclavicular
line and the midline and correlated these indings
with gender, age, height, weight, and body surface area. hey
found that organ size increases with height and body surface
area and decreases with age. he mean longitudinal diameter
of the liver in the midclavicular line in this study was 10.5 cm,
with standard deviation (SD) of 1.5 cm, and the mean midclavicular
anteroposterior diameter was 8.1 cm (SD 1.9 cm). In
most patients, measurement of the liver length suices to measure
liver size. Riedel lobe is a tonguelike extension of the inferior
tip of the right lobe of the liver, frequently found in asthenic
women.
he normal liver is homogeneous, contains ine-level echoes,
and is either minimally hyperechoic or isoechoic compared to
the normal renal cortex (Fig. 4.11A). he liver is hypoechoic
compared to the spleen. his relationship is evident when the
lateral segment of the let lobe is elongated and wraps around
the spleen (Fig. 4.11B).
FIG. 4.10 Right Triangular Ligament. Subcostal oblique scan near
dome of right hemidiaphragm (curved arrows). Note lobulated contour
and inhomogeneity of liver in this patient with cirrhosis. Right triangular
ligament (straight arrows) is visualized because of ascites.
Hepatic Venous System
Blood perfuses the liver parenchyma through the sinusoids and
then enters the terminal hepatic venules. hese terminal branches
unite to form sequentially larger veins. he hepatic veins vary
in number and position. However, in the general population,
there are three major veins: the right, middle, and let hepatic
veins (see Fig. 4.4). All drain into the IVC and, as with the portal
veins, are without valves. As discussed earlier, the right hepatic
vein is usually single and runs in the right intersegmental issure,
separating the anterior and posterior segments of the right lobe.
he middle hepatic vein, which courses in the main lobar issure,
forms a common trunk with the let hepatic vein in most cases.
he let hepatic vein forms the most cephalad boundary between
the medial and lateral segments of the let lobe.
Normal Liver Size and Echogenicity
he upper border of the liver lies approximately at the level of
the ith intercostal space at the midclavicular line. he lower
DEVELOPMENTAL ANOMALIES
Agenesis
Agenesis of the liver is incompatible with life. Agenesis of either
right or let lobes has been reported. 9,10 In three of ive reported
cases of agenesis of the right lobe, the caudate lobe was also
absent. 9 Compensatory hypertrophy of the remaining lobes
normally occurs, and results of liver function tests (LFTs) are
normal.
Anomalies of Position
In situs inversus totalis (viscerum), the liver is found in the
let hypochondrium. In congenital diaphragmatic hernia or
omphalocele, varying amounts of liver may herniate into the
thorax or outside the abdominal cavity.
Accessory Fissures
Although invaginations of the dome of the diaphragm have been
called “accessory issures,” these are not true issures but rather
diaphragmatic slips. hey are a cause of pseudomasses on
sonography if the liver is not carefully examined in both sagittal
and transverse planes (Fig. 4.12). True accessory issures are
uncommon and are caused by an infolding of peritoneum. he
inferior accessory hepatic issure is a true accessory issure that
stretches inferiorly from the right portal vein to the inferior
surface of the right lobe of the liver. 11
Vascular Anomalies
he common hepatic artery arises from the celiac axis and
divides into right and let branches at the porta hepatis. his
classic textbook description of the hepatic arterial anatomy occurs