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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_1260_Библиотеки_им_академика_М_И_Перельмана
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Imaging of hepatopancreatobiliary diseases 69
70 Chapter 5
Figure 5.5 A 71-year-old man with incidentally discovered lesion in the pancreatic tail. Small enhancing nodule identified on
contrast-enhanced CT (a) in the pancreatic tail could represent an intrapancreatic splenule or solid pancreatic neoplasm such as
neuroendocrine tumor. SPECT (b) and fused SPECT/CT (c) images from a heat-damaged RBC scan demonstrated uptake within the
nodule, diagnostic of intrapancreatic splenule.
5.2 Organ-specific imaging 5.2.1.2 MRI sequences, protocols, and
contrast agents
5.2.1 Liver Magnetic resonance imaging provides superior soft tissue
5.2.1.1 Imaging options
Ultrasoundis a usefulscreening modality, typicallyemployed lesions [34,35]. While the large number of sequences
in the setting of hepatocellular carcinomascreening in at-risk can be intimidating to the nonradiologist, each MR
patients with chronic liver disease. However, the imaging sequence provides unique and complementary informacharacteristics of focal lesions on US tend to be nonspecific, tionabout the tissue/lesionof interest. Generally speaking,
often requiring further work-up with CT or MRI. Multiphase there are T1- and T2-weighted sequences. T1-weighted
contrast-enhanced CT [16] or MRI is the examination of images can provide information regarding fat content
choice for the characterization of focal liver lesions detected within the liver and also are the basis for postcontrast
on ultrasound or portal venous phase CT [4,34]. imaging. T2-weighted sequences are most useful for
contrast resolution and characterization of focal liver
◀
Figure 5.4 A 75-year-old man with colon cancer status post resection developed colorectal metastases to the liver and underwent
right hemihepatectomy. The postoperative course was complicated by abscess formation at the resection margin, with subsequent
development of a fistula to the anterior abdominal wall (partially seen in (d) and (f)). On routine follow-up, the patient was found
to have elevated carcinoembryonic antigen (CEA) levels, and PET/CT detected disease recurrence at the site of a previously ablated
segment II lesion (a). Patient underwent Eovist-enhanced liver MRI the following week, with redemonstration of recurrence at the
ablation site on arterial phase (b) and hepatobiliary phase (c) images. Note the linear hypointensity extending anteriorly from the
lesion, representing the ablation tract. Eovist-enhanced MRI demonstrated two additional liver lesions, one in segment II measuring
12 mm (d,e) and a second in segment IVB measuring 14 mm (f,g). These surgically resected metastatic lesions were not detectable
on PET/CT.
Imaging of hepatopancreatobiliary diseases 71
evaluation of fluid-containing structures such as cysts,
bowel, biliary, and pancreatic ducts. MR sequences are
packaged into MR protocols constructed to best characterize a lesion and answer a specific clinical question.
There are two basic types of gadolinium intravenous
contrast agents available for MRI. They are classified by
their biodistribution profiles into extracellular and hepatobiliary agents. Extracellular contrast agents are excreted
through glomerular filtration while hepatobiliary agents
have both renal and variable hepatobiliary excretion (5%
for gadobenate dimeglumine [Multihance, Bracco Diagnostics] and 50% for gadoxetate disodium [Eovist, Bayer
Healthcare Pharmaceuticals]) [36]. Standard gadolinium
contrast agents are extracellular with enhancement of
organs and lesions reflecting the biodistribution of contrast
in the vascular and interstitial spaces. Enhancement patterns with these agents reflect differential vascularity of
lesions relative to the hepatic parenchyma (tumors with
neoangiogenesis tend to be hypervascular/hyperenhancing
during the arterial phase relative to the liver). Enhancement
of lesions with hepatobiliaryagents reflectsa combination of
thevascularityoflesionsaswellasdifferentialuptake
related to presence or absence of hepatocyte transporters.
Eovist is taken up by a transporter expressed in normal
hepatocytes but is not taken up by metastatic lesions,
resulting in hypointense (dark) lesions on hepatobiliary
phase images [37]. In contradistinction, focal nodular
hyperplasia lesions express normal hepatocyte transporters
and are iso- to hyperintense (similar to or brighter than) in
comparison with the background liver on hepatobiliary
phase images [38,39]. Use of a hepatobiliary contrast agent
therefore may be advised when the differential diagnosis
includes focal nodular hyperplasia.
5.2.1.3 Focal liver lesions
There are several benign liver lesions which have classic
postcontrast imaging features on both CT and MRI [34].
Hemangiomas are the most common benign focal liver
lesion. These lesions are classically described as demonstrating discontinuous, nodular, peripheral enhancement that
gradually fills in on subsequent postcontrast phases (Figure 5.6). A characteristic feature of hemangiomas on MRI is
Figure 5.6 A 51-year-old woman with incidental liver lesion. The lesion centered within the caudate bridge demonstrates classic MR
findings of hemangioma. On T2-weighted images (a), the mildly lobulated lesion is hyperintense. On T1 fat-saturated late arterial
phase (b), the lesion is hypointense to liver and demonstrates discontinuous peripheral nodular enhancement, with progressive
centripetal filling of contrast enhancement on the portal venous (c) and equilibrium (d) phase images.
72 Chapter 5
“light bulb” bright T2 signal intensity. This can be a discriminating feature when compared with other lesions, like
metastases, that show only intermediate T2 signal intensity.
Focal nodular hyperplasia (FNH) is another benign lesion
that has a characteristic appearance on MR and CT. Because
FNH contains normal hepatocytes, it can be easily and
confidently diagnosed with use of hepatobiliary contrast
agents, such as Multihance and Eovist, because they retain
contrast (appear bright) on the hepatobiliary phase images
(Figure 5.7). Hepatocellular adenomas have variable
Figure 5.7 A 52-year-old woman with history of melanoma found to have a liver lesion on outside hospital CT exam. MRI of the
liver demonstrates lesion in segment VI of the liver. This lesion is minimally hyperintense on T2 HASTE (a), hypointense on
precontrast fat-saturated T1 sequences (b), demonstrates moderate arterial enhancement (c) which equilibrates on the portal venous
(d) and equilibrium phase (e) images, without evidence of washout. The lesion demonstrates central enhancement on the
five-minute delayed images (f), while the remainder of the lesion remains isointense to liver. This isointensity persists into the
one-hour delayed images (g). These findings are classic for focal nodular hyperplasia.
Imaging of hepatopancreatobiliary diseases 73
Figure 5.8 A 70-year-old man with alcoholic cirrhosis and portal hypertension presents with liver lesion detected on outside hospital
imaging. MRI demonstrates liver lesion meeting imaging criteria for hepatocellular carcinoma. The round lesion within segment VIII
demonstrates arterial enhancement (a), enhancing pseudocapsule on the portal venous phase (b) and washout on equilibrium
phase (c) images.
appearance on MR and CT and may contain blood products
from prior hemorrhage [40]. On MRI, these lesions may
demonstrate intracellular lipid which is detectable on
gradient echo in-phase and opposed-phase images.
Hepatocellular adenomas can be suggested by imaging
in the a ppropr iate clinical context; however, the imaging appear ance is not pathognomonic and follow-up or
biopsy confirmatio n is often required.
Malignant liver lesions such as hepatocellular carcinoma,
cholangiocarcinoma, and metastases can also be characterized by MR and CT. The most important discriminating
feature for liver lesions is the enhancement pattern that
they display. Hepatocellular carcinomas(HCC) usually occur
in the setting of chronic liver diseaseand demonstrate arterial
enhancement, washout, and delayed enhancing “capsule”
(Figure 5.8) [41]. HCC may also demonstrate vascular invasion and tumor thrombus (Figure 5.9). Intrahepatic massforming cholangiocarcinomas demonstrate continuous
peripheral enhancement and central delayed contrast
enhancement, and they may show a peripheral thin rim
of washout on delayed postcontrast images (Figure 5.10).
These lesions are often associated with intrahepatic biliary
duct dilatation when they occur centrally. They may
demonstratecapsularretractionwhentheyoccurinthe
periphery of the liver [42]. Metastases have variable appearances, often depending on the site of tumor origin [43].
Generally speaking, most metastases, including colorectal [44] (Figure 5.11; see also Figure 5.4) and pancreatic [45]
adenocarcinomas, are hypovascular (enhance less than the
background parenchyma). Metastases from primaries such
as neuroendocrine tumor are hypervascular (enhance
brighter than the background liver during the arterial
phase) [46] (Table 5.4).
5.2.1.4 Diffuse liver disease
Diffuse liver disease, while not a surgical entity, is important in the presurgical planning of patients with focal liver
lesions. Hepatic steatosis is commonly encountered and
can be diagnosed by ultrasound, CT or MRI [47]. On
ultrasound, there will be diffusely increased echogenicity
of the liver when compared with the adjacent right
kidney [3]. On CT, this manifests as diffusely low attenuation of the liver, diagnosed on noncontrast images when
the liver is 10 Hounsfield units lower than the spleen [47].
Magnetic resonance imaging can quantitatively char-
acterize steatosis and iron deposition. In-phase and
74 Chapter 5
Figure 5.9 A 56-year-old man presenting with abdominal distension and pain was found to have an echogenic expansile mass in the
main portal vein. Grayscale image of the right portal vein (a) demonstrates echogenic thrombus expanding the vein, contiguous
with an ill-defined mass in the right hemiliver. Doppler interrogation of the portal venous waveform (b) fails to demonstrate normal
portal venous flow but instead demonstrates arterial signal secondary to vascularized tumor thrombus. Correlative oblique coronal
contrast-enhanced CT image (c) demonstrates infiltrative tumor thrombus within the main and right portal vein. Axial CT image
(d) demonstrates contiguous infiltrative tumor in the right hemiliver, with tumor thrombus also invading the IVC.
opposed-phase gradient echo sequences take advantage
of chemical shift artifact of fat and water protons. When
the liver becomes darker on the opposed-phase images
when compared with the in-phase images, this is referred
to as “dropout” and indicates intravoxel lipid as seen with
diffuse hepatic steatosis [48,49] (Figure 5.12). The degree
of dropout can be quantified as a fat fraction or percentage
of steatosis that has been shown to correlate with pathology [48]. Other diffuse processes that involve the liver,
such as hemosiderosis, can also be detected. In contrast to
dropout of hepatic steatosis, if the liver becomes darker on
the in-phase image compared with the opposed-phase
image, this reflects iron deposition in the liver [50] (Figure 5.13). The liver may also demonstrate abnormally
increased T2 signal intensity (appear brighter) and show
diffusion restriction in the setting of hepatitis and fibrosis.
5.2.2 Biliary
Several imaging modalities are available in the diagnostic
work-up of biliary tract diseases, some of which are invasive. Noninvasive imaging modalities include CT, MRI with
magnetic resonance cholangiopancreatography (MRCP),
ultrasound, and cholescintigraphy. Invasive modalities
include endoscopic retrograde cholangiopancreatography
(ERCP) and percutaneous transhepatic cholangiography
(PTC). These examinations are often complementary in
the work-up of various biliary conditions (Table 5.5).
Intrahepatic biliary duct dilatation is readily detectable on
US, CT, and MRCP/MRI. MRCP depicts the biliary tree in a
noninvasive fashion (Figure 5.14) and has been shown to be
superior to ultrasound in the detection of common bile duct
stones [51,52]. It is useful in the evaluation of both benign
and malignant entities of the biliarysystem, includingbiliary
Imaging of hepatopancreatobiliary diseases 75
Figure 5.10 A 49-year-old woman with no significant past medical history presented with a several-month history of right upper
quadrant discomfort. MRI was performed for further evaluation and demonstrated a large lobulated mass centered within the
caudate bridge. This mass was T2 hyperintense (a) and demonstrated mild arterial enhancement (b), mostly in the periphery which
demonstrates progressive centripetal enhancement on portal venous (c) and five-minute delayed (d) images. On the one-hour
delayed images (e), the lesion demonstrates a thin rim of peripheral washout, a feature seen with cholangiocarcinoma and
metastatic adenocarcinoma. Biopsy of the liver lesion demonstrated intrahepatic cholangiocarcinoma.
Figure 5.11 A 54-year-old man with previously resected colorectal cancer presents with new liver lesions. Liver MRI performed with
Eovist contrast in the hepatobiliary phase (20 minutes post contrast) demonstrated two hypointense liver lesions, the larger of the
two shown in the axial (a) and coronal (b) planes within segment II of the liver, abutting the left (a) and middle hepatic veins (b), as
well as the IVC. Although surgical resection of the two liver lesions was planned, intraoperative evaluation revealed peritoneal
implants, not visible on MR, consistent with metastatic disease. On palpation and intraoperative ultrasound, multiple other liver
lesions suspicious for metastases were discovered and the planned surgery was aborted.
76 Chapter 5
Table 5.4 Classic imaging appearance of select focal liver lesions.
Liver lesion Contrast enhancement Other findings
Hemangioma
Focal nodular hyperplasia (FNH)
Hepatocellular adenoma
Hepatocellular carcinoma
Intrahepatic cholangiocarcinoma
Peripheral nodular contrast enhancement with
centripetal fill-in of enhancement with time
Early, avid arterial enhancement
Isointense (stealthy) on later contrast phases
Retention of hepatobiliary contrast agent
Variable
Arterial enhancement with washout and delayed
“capsule” appearance
Peripheral arterial enhancement with gradual centripetal
enhancement and peripheral rim of contrast “washout”
T2 hyperintense (“light bulb” bright)
Isointense (stealthy) on T2
Central scar may enhance on delayed images
Typically T2 hyperintense
May contain lipid
May contain blood products
Typically mild T2 hyperintensity
May contain lipid
May show vascular invasion
Typically mild T2 hyperintensity
Capsular retraction
Intrahepatic biliary duct dilatation
Figure 5.12 A 49-year-old woman with diffuse hepatic steatosis. Gradient echo in-phase (a) and opposed-phase (b) MR images
show decrease in liver signal intensity on the opposed-phase images compared with the in-phase images, consistent with diffuse
hepatic steatosis.
Figure 5.13 MR images of the liver in a 41-year-old man with sickle cell anemia and history of multiple blood transfusions
demonstrate greater loss of signal within the liver, spleen, and to a lesser extent the bone marrow on gradient echo in-phase
(a) compared with opposed-phase (b) images consistent with iron deposition in the reticuloendothelial system in the setting of
secondary hemosiderosis.
Imaging of hepatopancreatobiliary diseases 77
Table 5.5
Comparison of imaging modalities in the evaluation of biliary disease.
Imaging modality Noninvasive Strengths Weaknesses
Computed
tomography Great spatial resolution/anatomical detail
Ultrasound
MRI/MRCP
Cholescintigraphy
ERCP Detailed evaluation of biliary tree Difficult in postbiliary-enteric anastomosis
PTC Evaluation of ducts upstream from level of
p
p
p
p
Readily available
Intrahepatic and extrahepatic ductal dilatation
well seen
Radiodense cholelithiasis and choledocholithiasis
may be seen
Assessment of sonographic Murphy’s sign Limitations by body habitus
Identification of acute cholecystitis Distal CBD and much of pancreas can be
Identification of cholelithiasis and difficult to visualize owing to bowel gas
choledocholithiasis
Comprehensive evaluation of biliary disease
Strictures, masses, choledocholithiasis well
evaluated
Assessment of biliary tract in postbiliary-enteric
anastomosis patients
Eovist can be used to produce enhanced biliary
imaging and assessment of bile leak
Assessment of physiology Poor anatomical detail
Detection of cystic duct obstruction in acute
cholecystitis
Detection of bile leak
Potential for therapeutic intervention (balloon patients
sweep/dilatation and stent placement) and duct Limited ability to opacify ducts upstream from
brushings stricture
obstruction
Identification of isolated ducts in iatrogenic bile
duct injuries
Potential for therapeutic intervention (drainage
catheter placement) and duct brushings
Cannot detect radiolucent biliary stones
Not as sensitive as MRCP for subtle stricturing
Eovist uptake and excretion may be impaired in
setting of severe cholestasis or liver dysfunction
Risk of post-ERCP pancreatitis/cholangitis
Risk of vascular injury and cholangitis
CBD, common bile duct; ERCP, endoscopic retrograde cholangiopancreatography; MRCP, magnetic resonance cholangiopancreatography;
MRI, magnetic resonance imaging; PTC, percutaneous transhepatic cholangiography.
strictures, primary sclerosing cholangitis, and cholangiocarcinoma [53]. In the setting of suspected primary sclerosing
cholangitis, MRCP performs well as an initial imaging test,
which is often followed up with an ERCP [54]. There is a
paucity of diagnostic accuracy studies comparing the performance of US, CT, and MRI in the evaluation of hilar
cholangiocarcinoma [55] (Figure 5.15). Most studies have
investigated the diagnostic performance of CT in staging
cholangiocarcinoma, with an accuracy of 86% in determining ductal extent of tumor [55].
Endoscopic retrograde cholangiopancreatography and
PTC both employ the common principle of injection of
contrast directly into the biliary tree (Figure 5.16). Both of
these techniques are invasive and can yield highly detailed
images of the bile ducts. ERCP is performed under sedation,
with endoscopists cannulating the common bile duct or
pancreatic duct and injecting contrast agent under force
in a retrograde fashion. The advantage of this technique is
the potential for intervention, such as balloon sweep of
filling defect, balloon dilatation of strictures, and placement
of decompressive stents upon identification of pathology.
PTC involves percutaneous needle injection of contrast
agent into the liver and not uncommonly involves multiple
attempts to opacify an appropriate bile duct. This technique
is useful in the evaluation of intrahepatic ductal dilatation,
which may not be evaluated by ERCP owing to prior biliary
78 Chapter 5
Figure 5.14 Thick slab MRCP image (a) demonstrates intrahepatic and extrahepatic biliary duct dilatation, the reason for which is
not evident until examining the coronal T2 fat-saturated thin-slice image of the biliary tree (b). This reveals an obstructing stone in
the distalmost common bile duct.
enteric surgery or high-grade stricture, or in the assessment
of iatrogenic bile duct injury, especially when intervention
such as placement of an internal/external biliary drain or U
tube is a therapeutic necessity [56]. PTC and ERCP are
typically performed after an initial assessment of the biliary
tree with noninvasive cross-sectional imaging.
In the setting of suspected bile leak, usually from iatrogenic injury, several diagnostic imaging modalities are
available. Patients are often first imaged by CT in the
postoperative setting because of abdominal pain or liver
function test abnormalities. This may reveal intraperitoneal
or perihepatic fluid suspicious for biloma. The etiology of
these fluid collections can be further evaluated by MRCP
with Eovist hepatobiliary contrast agent [57] (Figure 5.17)
or with a HIDA scan which will show extraluminal extravasation of excreted contrast or radiotracer, respectively.
Hepatobiliary phase MRCP images may demonstrate the
duct responsible for the biloma, but often ERCP and/or PTC
are required for definitive identification and preoperative
planning for repair.
5.2.3 Gallbladder
The gallbladder is affected by many benign entities as well
as carcinoma and, rarely, metastatic disease. The most
Figure 5.15 An 87-year-old man with multiple medical problems presented after his family noticed increased jaundice.
CT examination with image in an oblique coronal reformatted plane (a) demonstrates enhancing intraductal mass within the
common hepatic duct which causes intrahepatic biliary duct dilatation. This malignant stricture secondary to cholangiocarcinoma is
confirmed on ERCP (b) with brushings. IVC filter is also noted.
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