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Chapter 12 / Intraoperative Ultrasound of the Liver, Bile Ducts, andPancreas 141
will break down this big picture to smaller, usable, practical segments.
Pattern recognition is important in IOUS.
Echogenicity refers to the ultrasound appearance of tissues and
structures. Anechoic structures appear to be without echoes; hypoechoic
structures have fewer echoes, and hyperechoic structures have brighter
echoes than surrounding structures. (Fig. 12.2 shows the gallbladder lumen
FIGURE 12.1 Console of Aloka ultrasound unit. Gain knob is on bottom (long
arrows); TGC slider pots are on top right (short arrows).
FIGURE 12.2 IOUS of the gallbladder (short
arrow, note hyperechoic stones) in a patient
with portal vein thrombosis and cavernous
transformation (darker veins, long arrow).
Section II / Liver142
that is anechoic or hypoechoic relative to the adjacent liver parenchyma, as
well as hyperechoic stones in the gallbladder lumen.)
Signal transmission: begins with coupling of the transducer and
the structure being imaged. Coupling may be generated by direct probe
placement on the tissue to be imaged (liver, pancreas, etc.) or via “stand-
off ” through an acoustic window such as the stomach/duodenum.
Flooding the operative field with saline and using this fluid as an acous-
tic window is a useful standoff technique with which to evaluate super-
ficial lesions.
Probe types: Transducer frequencies ranging from 5 to 10 MHz are use-
ful for IOUS. Many IOUS probes are set at 7.5 MHz. e sound penetration of
these frequencies is 6 to 10 cm, which is acceptable for most IOUS applica-
tions. Most IOUS probes are linear array; the crystals may be arranged in
a linear fashion (which generates rectangular images) or curved orienta-
tion (also called convex probes). Probes may be of the “nger” or “T” shape.
Each probe shape has advantages and limitations. e operator should try
as many probes as possible; most will gravitate to one probe type or another
(i.e., nger or T). Laparoscopic probes may be rigid or articulate in one or
two orientations; the latter are particularly helpful when scanning the pos-
terior liver sections (Fig. 12.3).
Orientation: Two basic planes are recognized in ultrasound—longi-
tudinal and transverse. e operator should orient the probe (particularly
the T probe) by pattern recognition—the left lateral section of the liver is
a useful landmark with the “point” of the left lateral section aiming to the
left upper corner of the screen (Fig. 12.4). e right kidney also serves as a
good landmark.
FIGURE 12.3 Articulating laparoscopic transducers provide more range of tissue coverage.
Chapter 12 / Intraoperative Ultrasound of the Liver, Bile Ducts, andPancreas 143
Depth: can be adjusted in many ultrasound units (Fig. 12.1). Users
should remember that image “magnication” typically sacrices some
clarity.
Image renement: Once orientation and ideal scanning depth have
been established, the image is rened by adjusting the gain and time gain
compensation (TGC). Adjusting gain amplies the returning echo signal
(makes the image on the screen brighter). e gain should be set initially
to make structures known to be anechoic (such as blood vessels) black. Too
little gain results in nonvisualization of some structures; too much gain
results in image artifact. Sound waves attenuate as they pass through tis-
sue. e TGC controls are used to “ne tune” the depth of focus of IOUS
images, using the most sensitive area of the sound wave (the focal region of
transition from near eld to far eld) to interrogate the structure of interest.
Scanning techniques: systematic scanning is undertaken using four
basic probe movements—sliding, rotating, rocking, and tilting. e novice
ultrasonographer’s initial impulse is to slide the probe; however, a remark-
able amount of information can be learned simply by rocking and tilting
the probe from one discrete position. e operator must be aware of the
eect probe pressure exerts on the underlying tissue. Too much pressure
may compress vascular structures (Fig. 12.5) or obscure lesions. On the
other hand, deliberate compression (“compression scanning”) is a useful
technique for dening some structures. For example, in the porta hepatis,
the portal vein will compress, while the hepatic artery will not compress.
Special techniques: such as stando, acoustic window use, or intra-
vascular contrast-enhanced ultrasound may be applied to appropriate
situations.
FIGURE 12.4 Orientation relative to left lateral liver section. A. Correct orienta-
tion, edge of the liver at top right of screen (arrow). B. Backward orientation.
Section II / Liver144
FIGURE 12.5 Compression. A. Liver without compression. Note hepatic vein (short arrow),
portal vein branch (long arrow, note hyperechoic edges from extension of Glisson capsule
around the portal triad), and hyperechoic ligamentum venosum (dashed arrow). B. Probe is
in the same position, though with compression. Note ligamentum venosum (dashed arrow)
as anatomic reference; the vascular structures have been obliterated by the compression.
Chapter 12 / Intraoperative Ultrasound of the Liver, Bile Ducts, andPancreas 145
Mode: most ultrasound images are in gray scale “B” mode (bright-
ness modulation). Doppler mode may be used to evaluate vascular ow.
In Doppler mode, spectral analysis is plotted against time. Color ow uses
computer transformation of Doppler direction and velocity. By convention,
ow toward the transducer is red and ow away from the transducer is
blue. Velocity is typically shown in shades—darker shades indicate reduced
velocity, and brighter hues representing more rapid velocity.
Annotation and storage: Images may be stored either as static images
or as “cine” loop recording real-time scans.
Biopsy/ablation: biopsy or ablation may be directed precisely by ultra-
sound. It is critical to conrm needle position in two planes. A helpful tech-
nique is to apply color ow: moving the biopsy needle or ablation probe
under color ow visualization produces color motion marking.
Table 12.1 illustrates basic approach to IOUS scanning.
INTRAOPERATIVE ULTRASOUND OF THE LIVER
Intraoperative liver ultrasound is used to evaluate known lesions, identify
new lesions, and guide procedures (resection, ablation, biopsy). is guid-
ance also includes precisely localizing a lesion’s location relative to intra-
hepatic vascular structures, which has obvious therapeutic implications.
Despite advances in cross-sectional imaging, IOUS remains the most accu-
rate way to detect liver lesions; as many as 10% of patients will have unan-
ticipated additional liver lesions found at the time of IOUS evaluation. is
situation is particularly true for neuroendocrine tumors, many of which
have numerous occult intrahepatic metastases.
Intrahepatic metastases have a discrete acoustic character—they
may be isoechoic, hyperechoic, or hypoechoic relative to the surrounding
liver parenchyma (Fig. 12.6). Multiple metastases in the same patient nearly
always have similar echogenicity. erefore, the best approach to a patient
with known hepatic metastases is to rst identify a known lesion (i.e., one
that is palpable or easily seen on cross-sectional imaging) to determine
echogenicity. After identifying the echogenic characteristics of the known
lesion, the entire hepatic parenchyma should be scanned systematically,
keeping in mind the lesions’ character. Isoechoic lesions obviously are the
most challenging to detect intraoperatively.
In general, the approach to liver IOUS involves documenting vascular
inow and outow, followed by systematic evaluation of the parenchyma
with particular attention paid to target lesions’ relationship to vascular
1. Orientation—relative to known patterns such as left lateral liver section
2. Depth adjustment—will sacrice resolution for magnication
3. Image renement—gain and TGC
4. Systematic scanning
a. Movements—sliding, rotating, rocking, tilting
b. Compression scanning
c. Special techniques—standoff, acoustic windows
d. Mode adjustment—duplex, color ow
e. Biopsy/ablation (if indicated)
5. Annotation and storage
6. Completion scan
a
IOUS should be performed both prior to and after any dissection.
Basic Approach to IOUS Scanning
a
TABLE
12.1
Section II / Liver146
structures. Mobilization of the liver permits more accurate ultrasono-
graphic examination, though also creates supercial artifact. erefore,
liver IOUS should be performed both before and after mobilizing dissection.
Systematic Approach
Again, IOUS of the liver consists of inow, outow, and parenchymal evalu-
ation. Pattern recognition is important: an example is the fact that hepatic
veins have more acute angles of articulation than portal veins, which join at
more of a right angle. Particularly important to inow is evaluation of known
tumor relationship to vascular structures. An example of this concept is
a caudate tumor’s relationship to the inferior vena cava and portal vein.
Outow imaging documents hepatic vein drainage to the suprahepatic vena
cava as well as documentation of accessory right hepatic vein. Although
this anatomy is ideally known from preoperative imaging, the actual spa-
tial relationship to the vena cava is well visualized with the ultrasound. e
relationship of central tumors to the intrahepatic vasculature (particularly
the middle hepatic vein) is similarly quite important. Intravascular tumor
thrombus may be diagnosed by IOUS; this nding may dramatically alter
operative approach.
Hepatic parenchymal pathology such as cirrhosis, steatosis, and post-
chemotherapy changes signicantly aects ultrasound characteristics. e
hyperechogenicity of fatty liver or cirrhotic liver limits IOUS resolution.
Evaluation of the parenchyma should be performed in a systematic fashion,
that is, “lawn mowing” or segmental approach. No one perfect method for
parenchymal scanning exists; the operator should become familiar with an
approach and apply this approach consistently. As mentioned above, intra-
hepatic metastases may be hyper-, hypo-, or isoechoic to the underlying
FIGURE 12.6 Metastatic cholangiocarcinoma to the
liver (arrow). The lesion is hypoechoic to the surround-
ing hepatic parenchyma.
Chapter 12 / Intraoperative Ultrasound of the Liver, Bile Ducts, andPancreas 147
parenchyma; identifying the echogenicity of a known lesion early facilitates
systematic interrogation of the hepatic parenchyma. Parenchyma should
be scanned slowly. e operator should be cautious of supercial lesions
that may not be completely captured by ultrasound without using stando
techniques. e operator should also be aware of compression, too much
of which may obscure intrahepatic lesions. With increasing experience,
the ultrasound operator will become more comfortable adjusting TGC to
obtain more precise visualization of deep liver lesions. Perihepatic lymph
nodes particularly the portal nodes, celiac nodes, and retropancreatic
(aortocaval) nodes should also be evaluated at this point. Finally, postre-
section, evaluating ow in vascular structures with Doppler/ow mode,
is particularly useful after vascular reconstruction or to document portal
ow following a Pringle maneuver.
Pearls
■ Interoperative ultrasound of the liver may be limited in the setting of
hepatic parenchymal pathology such as cirrhosis and steatosis.
■ Do not “directly observe” intrahepatic radiofrequency ablation; the heat
may damage the sensitive ultrasound crystals as they contact the liver
surface.
■ For ultrasound-guided needle localization (radiofrequency ablation or
biopsy), the angle of needle placement may be challenging, and experi-
ence is helpful in determining this approach. Needle placement directly
adjacent to the ultrasound probe may not be the best position.
■ Validating probe position in two planes is mandatory prior to ablation.
is maneuver must be performed prior to ablation to avoid artifact.
Also, remember that ablation defects are not spherical.
■ Simple cysts of the liver are easily characterized; these lesions are
anechoic with posterior shadow (Fig. 12.7).
FIGURE 12.7 Classic features of simple
liver cyst: anechoic cyst with posterior
shadowing (arrows).
Section II / Liver148
■ Hemangioma of the liver may be conrmed by documenting ow through
the lesion (although this diagnosis is almost always secure preoperatively
with adequate IV contrast-enhanced cross-sectional imaging).
■ e ultrasound character of focal nodular hyperplasia and hepatic ade-
noma is very similar—these heterogeneous lesions are not possible to
distinguish by IOUS.
■ e posterior section and segment VII in particular is most challenging
to visualize with the laparoscopic ultrasound probe. A two-way articu-
lating probe is quite helpful evaluating these areas. Mobilizing the fal-
ciform and coronary ligaments also helps expose the posterior section
for IOUS.
■ It is important to complete laparoscopic IOUS through multiple port
sites.
■ Scoring the liver capsule with electrocautery provides a useful artifact
that helps dene the intrahepatic plane of resection.
INTRAOPERATIVE ULTRASOUND OF THE BILIARY SYSTEM
IOUS of the biliary system is most commonly used to visualize intrahe-
patic and extrahepatic stones as well as to evaluate the relationship of
biliary tumors to intra- and extrahepatic vascular structures. Less com-
monly, the diagnosis of biliary cystadenoma may be conrmed by visual-
izing septa and/or rarely a direct communication between cyst and the
biliary tree. e later is usually seen more clearly with magnetic resonance
cholangiography.
Systematic Approach
It is helpful to use an acoustic window (i.e., viewing through hepatic seg-
ment III or IV) to visualize the extrahepatic biliary tree. Similarly, either the
stomach or the duodenal bulb provides a good acoustic window to visual-
ize the intrapancreatic common bile duct. Of note, no Kocher maneuver
is necessary to image the intrapancreatic bile duct. If Kocher maneuver is
planned, ultrasonography should be performed both before and after dis-
rupting these tissue planes. e quality of ultrasound images decreases sig-
nicantly after dissection.
e course of the biliary tree should be dened. Particular atten-
tion should be paid to the aberrant biliary anatomy such as a low-lying
right posterior sectoral duct. The relationship of the biliary tree to vas-
cular structures (particularly the right hepatic artery) should be dened.
Figure 12.8 shows aberrant right hepatic artery coursing anterior to the
common bile duct. e presence of shadowing defects (e.g., intraductal
stones) should be sought. ree classic sonographic criteria for stones are
(1) presence of hyperechoic focus, (2) posterior shadowing, and (3) mobil-
ity (Fig. 12.9). Most stones are mobile with movement of the gallbladder
or bile duct—this distinguishes them from polyps or tumors, which are
xed. Gallbladder polyps may not shadow; generally, neoplastic polyps
are less echogenic than cholesterol polyps. Inltrating tumors may show
irregular wall thickening; attention should be paid to the interface of the
gallbladder wall with the hepatic parenchyma. Tumors of the gallbladder
fundus or extrahepatic biliary tree should be evaluated relative to their
relationship with adjacent vascular structures—portal veins and hepatic
arteries.
Although some skilled operators advocate IOUS as the sole modal-
ity to diagnose bile duct stones, it is important to realize that the learn-
ing curve for biliary IOUS is relatively steep. Many biliary surgeons
feel comfortable conrming ultrasound ndings with intraoperative
cholangiography.
Chapter 12 / Intraoperative Ultrasound of the Liver, Bile Ducts, andPancreas 149
Pearls
■ IOUS is helpful in identifying the course of an aberrant arterial structure
(i.e., replaced right hepatic artery, right hepatic artery anterior to the
common hepatic duct).
■ IOUS of the biliary system may actually be most useful in laparoscopic
surgery, where decreased tactile sensation is available.
■ IOUS is quite useful to evaluate the intrahepatic and intrapancreatic
extension of choledochal cysts.
■ With practice, ultrasonography allows identication of the common bile
duct and main pancreatic duct junction in the pancreatic head, that is,
an abnormal biliopancreatic junction.
■ IOUS is useful to localize the papilla for “targeted” (limited) duodenot-
omy for papillary exploration, such as sphincteroplasty, ampullectomy,
transsphincteric exploration.
■ IOUS is helpful to identify enlarged and possibly pathologic involved second
echelon lymph nodes in patients with cholangiocarcinoma and gallblad-
der cancer (i.e., celiac, retropancreatic, aortocaval nodes). Many authorities
consider involvement of these nodes to be a contraindication to resection.
■ In gallbladder cancer, ultrasound is important in evaluating tumor rela-
tionship to the portal vein and the hepatic artery.
■ In Mirizzi syndrome, ultrasound is quite useful for evaluating the biliary
tree in relationship with the surrounding vascular structures and posi-
tion of the stone.
■ Pressure from the ultrasound probe in the porta hepatis will compress
the portal vein but not the hepatic artery.
■ Intrahepatic bile ducts are typically not visible on ultrasound scanning.
erefore, any intrahepatic biliary dilation visible on IOUS suggests
biliary pathology.
FIGURE 12.8 Transhepatic acoustic window visualizing extrahe-
patic biliary tree. Aberrant right hepatic artery (arrows) passing
anterior to dilated common bile duct (star).
Section II / Liver150
FIGURE 12.9 Laparoscopic IOUS of common bile duct stone
(arrow) shown in transverse (A) and sagittal (B) orientation.
The stone is hyperechoic with posterior shadowing.