is an Assistant Clinical Professor, University of California-San
Francisco (UCSF) and a Staff Radiologist, San Francisco Veterans
Administration Medical Center (SFVAMC).
is the Vice Chair of Radiology, UCSF and the Chief of Radiology,
SFVAMC, San Francisco, CA.
The imaging of pancreatic masses has evolved considerably since
the introduction of multidetector computed tomography (MDCT). This
new technology has enabled the acquisition of thinner slices during
multiphasic scanning, with improved spatial resolution of axial,
multiplanar reformatted, and 3-dimensional (3D) images. Pancreatic
adenocarcinoma is the most common malignancy of the pancreas and
accounts for up to 90% of all pancreatic tumors. Other, less common
causes of pancreatic masses include solid tumors (such as islet
cell tumor [ICT]), lymphoma, mesenchymal tumor, metastasis to the
pancreas as well as a variety of cystic lesions. Inflammatory
masses of the pancreas related to either acute or chronic
pancreatitis may also simulate a pancreatic neoplasm (Figure
MDCT allows multiphasic contrast-enhanced scans of the pancreas,
so that data is acquired during optimal pancreatic enhancement,
aiding tumor detection. Optimum vascular opacification is also more
reliable, enabling assessment of vascular invasion by tumor. The
pancreas may also be scanned using thinner slices, which improves
resolution and can aid in the detection of smaller lesions.
Water is the preferred oral contrast agent because it is well
tolerated by patients and acts as an excellent negative contrast
agent that allows for improved visualization of the duodenum and
the small bowel when intravenous contrast is given.
A negative oral contrast agent is also helpful if postprocessing
techniques are to be used to evaluate pancreatic vessels.
Accurate timing of the data acquisition is dependent on the type
of CT scanner utilized, the rate of contrast administration, and
the patient's cardiac output.
A fast contrast injection rate of at least 3 to 4 mL/sec is
essential for optimal tissue enhancement. Bolus-tracking software
is commercially available to help with accurate timing of CT data
acquisition during the various phases following contrast injection.
MDCT allows for rapid scanning of the abdomen-from the level of the
diaphragm to the iliac crest in <20 seconds.
Multiphasic scanning of the pancreas involves an initial
noncontrast-scan series through the abdomen for pancreas
localization. This is followed by scanning the pancreas during
arterial, pancreatic, and venous phases. Arterial-phase scans are
acquired 20 seconds after the start of the intravenous contrast
injection. Arterial-phase images are necessary if CT angiography
(CTA) is being performed. The pancreatic phase is performed 40
seconds after the start of contrast injection. The pancreatic
parenchyma typically enhances maximally during this phase.
Several studies have found that the majority of pancreatic lesions
are optimally visualized during the pancreatic phase.
The final phase is the venous phase, which is acquired 60 to 65
seconds after the start of contrast injection. During this phase,
the mesenteric arteries and veins achieve maximum enhancement,
which is essential for the accurate depiction of vascular invasion.
This phase is also the most sensitive for identifying hepatic
metastases. The timing of the different phases of the CT study may
be adjusted manually to accommodate for variables such as the
patient's cardiac output and body habitus when bolus-tracking
software is not employed.
The CT data is available for postprocessing following scan
completion. There are many commercially available computer software
packages that allow rapid multiplanar reconstructions and 3D
renderings. The user can manually trace the pancreatic or biliary
ducts to create curved planar reconstructions (Figures 2 and 3).
Further manipulation of the CT data set can be performed using 3D
techniques, such as maximum intensity projection (MIP) and volume
rendering. Real-time manipulation of the CT data generates images
in multiple planes to best depict the pancreas and adjacent
Pancreatic adenocarcinoma has a dismal prognosis with a 5-year
survival rate of 5%.
Survival improves when early-stage smaller lesions are detected. A
study by Ariyama et al
reported a 5-year survival rate of 100% for patients with tumors
<1 cm if these tumors were limited to the intraductal epithelium
without parenchymal, vascular, or lymphatic invasion. However,
survival rates fell precipitously with increasing lesion size.
Studies have reported survival rates of 30% for lesions measuring
<2 cm in diameter.
Unfortunately, only a minority of patients with pancreatic cancer
have localized disease at presentation; therefore, it is crucial to
detect early-stage tumors to identify patients who are suitable for
curative surgical resection.
The detection rate for smaller tumors has been disappointing,
with studies reporting sensitivities of 67% and 58% for lesions
<1.5 cm and 2 cm, respectively.
A recent study by Bronstein et al
found improved lesion detection, reporting a sensitivity of 77% for
pancreatic tumors that are <2 cm in size, with a specificity of
100%. This study was partially performed using MDCT with narrow
collimation (2.5 mm). Contrast-enhanced triple-phase scans were
performed using arterial phase, pancreatic parenchymal phase, and
portal venous phase scans.
The accuracy of single-detector CT for the detection of
pancreatic masses of all sizes is higher, ranging from 75% to 90%.
Further improvement has been achieved since the introduction of
MDCT. McNulty et al
detected 27 of 28 (96%) pancreatic carcinomas (mean tumor size of
3.3 cm) using MDCT. They reported that maximum enhancement of the
pancreas occurred during the pancreatic parenchymal phase. The
maximum tumor-to-parenchyma attenuation difference during the
pancreatic parenchymal phase and portal venous phase was
equivalent, with no significant difference seen subjectively. It
was noted that both of these phases were superior to the arterial
phase. Maximum arterial enhancement was seen during the pancreatic
parenchymal phase, and maximum venous enhancement was seen during
the portal-venous phase. The study concluded that the pancreatic
parenchymal phase and the portal-venous phase are sufficient for
the detection of the pancreatic adenocarcinoma and that the
arterial phase may be reserved for those patients who require CTA.
MDCT features of pancreatic adenocarcinoma
Adenocarcinoma of the pancreas consists of a dense fibroblastic
stroma with reduced vascularity in comparison with normal
Tumor tissue enhances less than normal pancreatic tissue does and
appears as a hypodense mass on contrast-enhanced CT. Larger tumors
may distort the pancreatic contour and extend to infiltrate
adjacent structures. Obstruction of the main pancreatic duct distal
to the tumor is often present because these tumors originate from
ductal epithelium. Adenocarcinoma located in the pancreatic head
may also cause obstruction of the common bile duct, giving rise to
the double-duct sign (Figure 2B).
Smaller pancreatic masses may be difficult to visualize because
their small size causes no gland distortion or because they are
isoattenuating to normal pancreatic parenchyma. A study by Prokesch
that used contrast-enhanced CT found that 11% (6 of 53) of
pancreatic tumors were not visualized directly on either pancreatic
or venous phases. Therefore, ancillary findings of pancreatic
carcinoma (including atrophy of the pancreas distal to a mass,
convex deformity of the pancreatic contour, or abrupt termination
of a dilated pancreatic duct
[Figure 3C]) are helpful in detection. The pancreatic duct may
become dilated either because of tumor or chronic pancreatitis, and
it is often impossible to make the distinction on contrast-enhanced
Pancreatic adenocarcinoma readily extends to the peripancreatic
fat and vessels, especially since the pancreas lacks a capsule.
Tumor resectability depends on the extent of local extension or
vascular involvement in the absence of distal metastases.
Lu et al
proposed a CT-based grading system for determining vascular
involvement by pancreatic carcinoma. The authors prospectively
graded vascular involvement using the pancreatic phase. A scale of
0 to 4 was used based on the degree of circumferential contiguity
of tumor to vessel, where 0 was no contiguity and 4 was >75%
contiguity. These criteria were applied to both arteries and veins,
and it was found that if >50% of the vessel circumference
(grades 3 and 4) was in contact with tumor, then there was a high
likelihood of the tumor being unresectable. A sensitivity of 84%
and a specificity of 98% were found for determining tumor
resectability based on vascular involvement.
The use of MDCT improves the resolution of sagittal and coronal
multiplanar reformatted images and allows for improved detection of
changes in vessel caliber
(Figures 4, 5, and 6). Diehl et al
reported that helical CT with dual-phase imaging was able to detect
vascular invasion in 35 of 40 (88%) patients with pancreatic
adenocarcinoma and a negative-predictive value of 79% for
determining nonresectability. Raptopoulos et al
obtained CT angiograms in 82 patients and found that CTA improved
the accuracy of diagnosing unresectable pancreatic carcinoma. The
addition of CTA to conventional axial helical CT resulted in a
negative-predictive value for determining tumor resectability of
96% compared with 70% for conventional axial helical CT alone.
Vargas et al
evaluated the resectability of pancreatic carcinoma using MDCT and
found an overall negative-predictive value of 87%. The negative
predicative value for detecting vascular invasion with the use of
curved planar reformats was 100%.
Local lymph node spread
The lymphatic drainage of the pancreas is primarily to the
pancreaticosplenic nodes that accompany the splenic artery. Some
drainage also occurs to the pancreaticoduodenal nodes and the
superior mesenteric preaortic nodes.
The detection of metastases involving these lymph node groups in
patients with pancreatic cancer on CT remains challenging.
The main criterion used to assess tumor metastases to lymph nodes
is nodal enlargement. However, all enlarged nodes do not
necessarily contain tumor, and all normal-sized nodes may not
necessarily be free of tumor. Zeman et al
found nodal staging accuracy to be only 58% when evaluating TNM
staging of pancreatic carcinoma using helical CT. Muller et al
found a sensitivity and specificity of only 22% and 57%,
respectively, for the detection of nodes involved by pancreatic
cancer. A study by Diehl et al
showed that nodal involvement was detected in only 54% of cases,
but the overall accuracy of CT for staging pancreatic cancer
remained high at 91%. The accuracy of readers in determining
resectable versus unresectable disease was much higher at 96% and
Regional lymph nodes are typically resected at surgery; hence,
nodal enlargement is not considered a contraindication to surgery
if there are no other signs of advanced disease.
The liver is a common site for pancreatic metastases, and their
detection is critical for accurate staging. Hepatic metastases are
best seen during the portal-venous phase of enhancement, and they
typically appear as low-attenuation lesions compared with adjacent
normally enhancing liver parenchyma.
Metastases from pancreatic carcinoma are also commonly seen in the
lungs and peritoneum.
Excellent results have been found using helical CT for the
identification of patients with unresectable disease due to
However, CT does not perform as well in identifying resectable
pancreatic carcinoma. Patients may be understaged because of missed
small hepatic metastases and peritoneal deposits. Bluemke et al
found that 42% of patients were inaccurately staged because of
missed liver metastases. The routine use of thin collimation is
essential and can aid in the detection of lesions <5 mm.
Unfortunately, liver lesions that are this small are difficult to
characterize accurately, limiting the specificity of
contrast-enhanced CT. These small hepatic lesions may represent
cysts or hemangiomas as well as metastases. The sensitivity of
dual-phase helical CT for detecting hepatic metastases is only 75%.
Most missed liver lesions are <1 cm in size or are surface
lesions that are detected only during surgery.
Other pancreatic masses
Islet cell tumors
Islet cell tumors arise from neuroendocrine cells in the
pancreas, with an incidence of 5 cases per million persons per
These cells are classified as functioning or nonfunctioning.
Patients with functioning ICTs represent approximately 75% of all
neuroendocrine tumors and usually present with symptoms related to
excessive hormone production. Nonfunctioning ICTs do not produce
active hormones and are typically diagnosed incidentally or because
of mass effect. Even if malignant, ICTs have a favorable prognosis
when compared with pancreatic adenocarcinoma with a 5-year survival
rate of approximately 50%.
Since ICTs are often slow-growing indolent tumors, aggressive
management is justified even if the tumor has metastasized.
Functioning ICTs are often diagnosed prior to imaging by the
detection of elevated hormonal levels. The main role of imaging,
therefore, is to precisely locate and map the number and size of
these lesions to aid in surgical resection.
Functioning ICTs are named according to the hormones they produce.
Insulinomas are the most common and are usually benign. Patients
with insulinoma typically present with episodes of hypoglycemia
that are associated with elevated levels of plasma insulin.
Gastrinomas are the second most common and are usually malignant.
Patients with gastrinomas may present with symptoms of peptic ulcer
disease, abdominal pain, and diarrhea. Other functioning ICTs (such
as vipomas, glucagonomas, stomatostatinomas, and
corticotrophinomas) are much less common, representing only
approximately 5% of all ICTs.
Nonfunctioning ICTs are often larger than functioning ICTs at
initial presentation. These tumors are typically diagnosed when
patients experience symptoms related to the size or location of the
lesion. The presenting symptoms are nonspecific, including
abdominal pain and weight loss. An increasing number of
asymptomatic nonfunctioning ICTs are being discovered incidentally
because of the increased use of cross-sectional imaging studies.
MDCT imaging features
Islet cell tumors are highly vascular tumors with similar
enhancement characteristics for both functioning and nonfunctioning
ICTs. These lesions enhance more intensely than the normal
pancreatic parenchyma during both the arterial and venous phases.
This characteristic is helpful in differentiating these lesions
from other pancreatic masses, such as adenocarcinomas, which are
hypovascular. Multiphasic MDCT plays an essential role in the
detection of small ICTs. Their detection is dependent upon
correctly timing image acquisition relative to injection of the
intravenous contrast bolus.
The hypervascular nature of ICTs suggests that they are best
seen during the arterial or pancreatic phase (Figure 7). This has
been confirmed by studies that have measured the mean attenuation
difference between the lesion and the surrounding pancreatic
In a series of patients with functioning ICTs, Van Hoe et al
reported that most lesions were hyperenhancing but only a few were
more conspicuous during the arterial phase. A study by Ichikawa et
found no significant difference in the enhancement of ICTs when
comparing the arterial and venous phases. Some tumors have an
atypical enhancement pattern, particularly if they are larger with
regions of necrosis, which will appear hypo- or isoenhancing to the
normal pancreatic parenchyma during different enhancement phases
(Figure 8). Therefore, it is essential to analyze the venous phase
as well as the arterial and pancreatic phases.
In addition to local tumor extension, the liver and regional
lymph nodes are common sites for metastases. Metastases to the
liver are often hypervascular and are best appreciated during the
The sensitivity of helical CT in localizing functioning ICTs is
relatively low, with studies reporting 71% to 82%.
This has been attributed to the fact that ICTs, particularly
insulinoma tumors, are often small and difficult to visualize.
Endoscopic ultrasound provides an alternative imaging tool, with
Anderson et al
reporting a sensitivity and specificity of 93% and 95%,
respectively, for ICT detection.
Lymphoma that involves the pancreas is usually non-Hodgkin's
lymphoma (of the B-cell type). The pancreas typically becomes
involved by direct extension from peripancreatic lymph nodes.
Primary pancreatic lymphoma is much less common and is associated
with host immunosup-pression or human immuno-deficiency virus (HIV)
Pa- tients with pancreatic lymphoma present with symptoms such as
weight loss and abdominal pain. Acute pancreatitis and small bowel
obstruction have also been described as complications of pancreatic
Pancreatic lymphoma rarely presents with obstructive jaundice or
Pancreatic lymphoma has 2 main morphologic patterns-it can
appear as either a focal poorly enhancing, homogeneous soft tissue
mass or as diffuse infiltration of the pancreas, causing
enlargement of the entire gland.
The latter appearance may be mistaken for acute pancreatitis on
Pancreatitis has also been reported in association with pancreatic
lymphoma, presumably triggered by invasion of the pancreatic
parenchyma. The peripancreatic vessels may become encased by
lymphomatous tissue. However, dilatation of the pancreatic duct and
bile duct is uncommon and is a helpful feature in differentiating
this condition from pancreatic adenocarcinoma.
Lymphadenopathy located below the level of the renal veins is also
more commonly associated with lymphoma and is unusual for
If the imaging findings are atypical for pancreatic adenocarcinoma
and there is clinical suspicion of lymphoma, image-guided biopsy
can help confirm the diagnosis.
Mesenchymal tumors of the pancreas
Mesenchymal tumors are rare and represent approximately 1% of
pancreatic neoplasms. These tumors arise from connective, vascular,
or neuronal tissue in and around the pancreas. They are classified
by their histological appearance and include schwannomas,
neurofibromas, lymphangiomas, teratomas, and lipomas.
Giant cell tumor of the pancreas
These are rare tumors with 2 distinct histological types: 1) a
pleomorphic type, containing pleomorphic mononuclear and
multinuclear giant cells; and 2) an osteoclastic type, consisting
of osteoclast giant cells. The latter type is less common but is
associated with a better prognosis. The CT appearance of the
osteoclastic type is that of a large exophytic hypervascular mass
with areas of hemorrhage and necrosis (Figure 9). Giant cell tumors
of the pancreas may be mistaken for extrapancreatic tumors because
of their exophytic appearance.
Metastases to the pancreas
The majority of metastases to the pancreas originate from the
kidney, followed by the lung, breast, colon, melanoma, and soft
Patients with pancreatic metastases usually present with symptoms
related to their primary malignancy or to mass effect from
pancreatic masses, such as abdominal pain, jaundice, and weight
loss. Metastases to the pancreas may appear as a well-defined mass;
alternatively, multiple small lesions or diffuse gland enlargement
due to infiltration may be seen. The pancreatic duct may also
become dilated due to obstruction.
Cystic pancreatic masses
Pancreatic serous cystadenomas are rare neoplasms that occur
more commonly in women (female to male ratio of 2:1) usually over
the age of 60 years.
Symptoms are nonspecific, such as weight loss, malaise, anorexia,
and fatigue. These tumors are often found in the head and neck
region of the pancreas and may be large at presentation, although
biliary obstruction is not typically present.
Serous cystadenomas are composed of multiple small (<2 cm)
cystic areas, each of which resembles a bunch of grapes. The very
small cysts can have a honeycomb appearance on cross-sectional
imaging. The central fibrous stroma is often hypervascular and may
calcify, thus exhibiting the characteristic centrally located
calcified stellate scar (Figure 10). However, this is seen in only
a minority of patients (18%).
Although these lesions are benign, they may occasionally be
mistaken for malignant mucinous cystic neoplasm.
Mucinous cystic neoplasm
Mucinous cystic neoplasms are rare lesions that occur
predominantly in women (female to male ratio of 9:1), usually at a
younger age than serous cystadenomas. They usually occur in the
body and tail of the pancreas and are often large at presentation
(>10 cm in diameter).
Symptoms are nonspecific, related to local mass effect that causes
adjacent organ displacement or compression.
The differentiation of mucinous cystic neoplasms from other
cystic lesions of the pancreas is crucial because of their
malignant potential, with a reported 5-year survival rate of 17% to
Mucinous cystic neoplasms may be composed of several cystic areas
with each cyst typically >2 cm in diameter or may be a solitary
large cystic lesion
(Figure 11). The presence of septations or solid nodules within the
wall of the cysts can help differentiate them from other cystic
lesions. Such features are uncommon in serous cystadenomas and
Calcification, if present, is peripheral and curvilinear.
In a study by Procacci et al,
the presence of calcification, a thick cyst wall (>2 mm), and
septations correlated with a 95% risk of malignancy. Patients with
questionable cystic lesions should undergo percutaneous cyst
Intraductal papillary mucinous tumor
Intraductal papillary mucinous tumor (IPMT) of the pancreas
typically occurs in men who are older than 60 years.
Patients with IPMT often present with symptoms of recurrent
abdominal pain or unexplained weight loss. The absence of
predisposing etiologic factors for chronic pancreatitis (eg,
alcohol abuse and hyperlipidemia) should alert the clinician to the
possibility of an IPMT.
There are 3 types of IPMT: A main duct form that causes diffuse
or segmental dilatation of the main pancreatic duct; a branch duct
form that causes cystic dilatation of the branch ducts; and a mixed
form with elements of both types. Typical features seen on CT are
segmental or diffuse dilatation of the main pancreatic duct (MPD)
>2 mm and/or cystic lesions corresponding to dilated branch
ducts that are usually in the uncinate process. These findings may
be seen together or individually
(Figures 12 and 13). Gland atrophy is often present, and dysmorphic
calcifications may be seen in the dilated duct.
However, pancreatic calcifications seen with chronic pancreatitis
are typically not present. Endoscopic retrograde
cholangiopancreatography can help confirm the diagnosis by showing
mucin emanating from a bulging papilla with a dilated MPD.
The introduction of MDCT and postprocessing techniques with 3D
manipulation of the data set have greatly improved imaging of the
pancreas. These advances should further facilitate early detection
of small pancreatic lesions and are likely to impact the treatment
of pancreatic tumors, especially pancreatic adenocarcinoma. The use
of multiplanar reformatted images and 3D representation of the
vascular structures helps in accurate staging of pancreatic tumors
and aids in successful surgical resection.