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Archived Issues of Radiology Rounds
MGH Department of Radiology Website
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Cystic Pancreatic Lesions
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- High-resolution multi-detector CT is the preferred imaging
modality both for the detection and initial characterization of
pancreatic cystic lesions
- MRI with MR cholangiopancreatography (MRCP) accurately depicts
the cystic morphology and can demonstrate the relationship of the cyst
to the pancreatic duct
- Imaging with CT and/or MRI can characterize many pancreatic
cysts; if indeterminate, endoscopic ultrasound provides high-resolution
information and the opportunity to aspirate and biopsy suspicious areas
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As
cross-sectional imaging has become more common, there has been a marked
increase in the incidental detection of cystic pancreatic lesions. It
is estimated that more than a third of these are found in asymptomatic
patients. Although knowledge of the natural history of cystic lesions
is incomplete at this time, it is known that some cystic pancreatic
lesions, including pseudocysts and serous cystadenomas, have an
extremely low potential for malignancy while most mucin producing
cystic lesions have malignant potential. However, in general, the
prognosis for cystic neoplasms is better than pancreatic ductal
adenocarcinoma.
Pancreatic resection is major surgery
that has a high rate (30%) of complications and may precipitate
diabetes. Therefore, accurate characterization of cystic lesions and
assessment of the risk of malignancy is essential in order to avoid
resection of low risk lesions, especially when they are located at the
head of the pancreas. Resection may be considered when symptomatic,
large, or pre-malignant lesions are found. In these cases, patients
should be referred to a gastrointestinal surgeon specializing in
pancreatic surgery, who can weigh the risks and benefits of pancreatic
resection for each individual patient.
Our understanding of the biology and the use of imaging for the
diagnosis of cystic pancreatic lesions is rapidly evolving. The
guidelines recommended here are based on current knowledge and may be
revised in the future when more data on sensitivity and specificity
become available. Multi-detector CT and MRI can help classify cystic
pancreatic lesions by morphology into four sub-types, unilocular cysts,
microcystic lesions, macrocystic lesions, and cysts with a solid
component. Multidetector CT may be sufficient to assess the risk of
malignancy and to plan patient management if the cyst is > 3 cm. For
smaller cysts, the better image contrast of MRI makes it easier to
visualize septa and small solid components and MRCP can be used to
visualize a connection between the cyst and pancreatic duct, if present.
CT and MRI can characterize many pancreatic cysts. However, cross
sectional imaging can sometimes be confounded by morphological overlap,
in which case, endoscopic ultrasound (EUS) combined with
ultrasound-guided fine needle aspiration (FNA) is recommended for
further diagnostic evaluation. The aspirated cyst fluid should be
examined for mucin, cytology, and tumor markers. The accuracy of EUS
alone for distinguishing between mucinous cysts from non-mucinous
cystic lesions is 51%, whereas the accuracy of concurrent FNA of the
cyst fluid CEA is 79% and cytology 59%.
Unilocular Cysts
Unilocular cysts are those without internal septa, a solid component,
or central cyst wall calcification. Of this subtype, pseudocysts are
the most common, in which case the patient nearly always presents with
a clinical history of pancreatitis. Pseudocyst diagnoses are supported
by imaging findings of inflammation, atrophy or calcification of
pancreatic parenchyma, and dilatation of and calculi in a typically
thin walled cyst. Rarely, communication of a pseudocyst with the
pancreatic duct may be be seen by MRCP or CT. Pseudocysts
are benign and only symptomatic patients need to consider intervention
(cyst drainage or surgery).
Less commonly, unilocular cysts may be intraductal papillary mucinous
neoplasms (IPMNs), unilocular serous cystadenomas, or lymphoepithelial
cysts. In these cases, there is no clinical, laboratory, or imaging
evidence of pancreatitis. Multiple unilocular cysts are most often
pseudocysts from prior pancreatitis but may also be due to von
Hippel-Landau disease or, rarely, IPMN.
Patients with small asymptomatic thin walled unilocular cysts can be
monitored with serial CT or MRI but symptomatic patients and those with
thin walled unilocular cysts > 4 cm should be evaluated further.
Wall thickening, especially if irregular, is suggestive of a more
agressive lesion, which is best evaluated with EUS guided FNA.
Microcystic Lesions
Benign serous cystadenomas are the only microcystic lesions. Typically,
they are seen as a pattern of six or more cysts that range from a few
mm up to 2 cm in size. In some cases, there may be a single dominant
microcavity or there may be a few large cysts (> 2 cm), in which
case the diagnosis may be indeterminate and require EUS with FNA for
futher evaluation. Serous cystadenomas are benign and, therefore,
imaging surveillance is generally sufficient in asymptomatic patients
although patient management may be influenced by factors such as
patient age. If symptomatic or if the serous cystadenoma is > 4 cm,
patients should be referred for surgical evaluation.
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CT of a pseudocyst, a unilocular cyst (arrow)
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Macrocystic Lesions
Macrocystic lesions not only have larger compartments (> 2 cm
in diameter) but also fewer compartments than microcystic tumors.
Mucinous cystic neoplasms and IPMNs are found in this category,
as well as uncommon non-functioning neuroendocrine tumors and rare
congenital malformations.
About 75% of mucinous cystic neoplasms are asymptomatic. When symptoms
do occur, they are generally due to the mass effect of these lesions,
which can be quite large. Mucinous cystic neoplasms do not communicate
with the pancreatic duct but can cause partial pancreatic duct
obstruction, resulting in symptoms of pancreatitis. Occasionally, they
may contain debris or hemorrhage. MRI or EUS can show the complex
architecture of the mucinous cystic neoplasms better than CT; but the
peripheral “eggshell” calcification seen with CT, although seen in
<20% cases, is a feature specific for these lesions and is thought
to be predictive of malignancy .
IPMNs
may be found in the main pancreatic duct and/or its side branches.
Those in the main pancreatic duct are morphologically distinct from
cystic pancreatic tumors. However, if an IPMN is in a side branch or
extends into the main duct from a side branch, it may difficult to
distinguish from a mucinous cystic neoplasm. Although lack of
communication with the main duct does not rule out an IPMN, the
presence of communication is highly suggestive of an IPMN. Both MRCP
and thin-slice high resolution multi-detector CT can be used to look
for communication. Thus, endoscopic retrograde cholangiopancreatography
is now rarely needed for a diagnosis of IPMN. However, in select
patients, EUS-guided FNA may be needed for assessing the risk of
malignancy.
About 60% of IPMNs that affect the main
duct are malignant, which is not so for most IPMNs that affect the side
branch only. The latter type are considered pre-malignant although
preliminary data from MGH suggest that IPMNs < 3 cm have a low
potential for malignancy.
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| Endoscopic US: Demonstrates internal septations in a small cyst |
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| MRCP of a side branch IPMN, a septated cyst communicating with main pancreatic duct (arrow) |
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CT of a malignant mucinous cyst, a septated cyst with an associated solid mass (arrow) |
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| Pancreatic Cystic Lesion |
Malignant Potential |
Recommendation |
| Indeterminate from CT and/or MRI |
Unknown |
Refer to gastroenterologist for EUS-FNA |
| Symptomatic pseudocyst |
Very low |
Refer to surgeon* |
| Asymptomatic thin wall unilocular cyst, < 4 cm |
Very low |
Serial imaging at 6 months, 12 months, then annually for 3 yrs |
Symptomatic or
asymptomatic thin wall unilocular cyst, > 4 cm |
Low |
Refer to surgeon
For poor surgical risk patients, EUS should be used to assess risk of malignancy |
| Unilocular cyst with irregular, thickened wall |
Moderate |
Refer to surgeon |
| Asymptomatic serous cystadenoma, < 4 cm |
Very low |
Serial imaging annually for 3 yrs |
Symptomatic or
asymptomatic serous cystadenoma, > 4 cm |
Low |
Refer to surgeon.
For poor surgical risk patients, EUS should be used to assess risk of malignancy |
| Side branch IPMN |
Moderate |
Refer to surgeon |
| Main branch IPMN, mucinous cystic neoplasms with or without solid component |
High |
Refer to surgeon |
| *Patients should be referred to a gastrointestinal surgeon specializing in pancreatic resection. |
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Cysts with a Solid Component
Cysts with a solid component, whether they be unilocular or
multilocular, are either malignant or have a high malignant potential.
MRI with MRCP is considered to be superior to CT for the detection of
small mural nodules. However, inspissated mucin or calcification in the
cyst may mimic a mural nodule in MRCP and small nodules may be missed
by both MRI and CT. Alternatively, high resolution EUS is sensitive for
the detection of nodules.
Scheduling
Appointments
for CT, MRI, and MRCP can be scheduled at Mass General West Imaging,
Waltham, Mass General Imaging, Chelsea, or at the main MGH campus
through the Radiology Order Entry system, http://mghroe
or by calling
617-724-9729 (Radiology). MRI and MRCP can also be scheduled at Mass
General MRI, Charlestown Navy Yard.
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Further Information
For further questions, please contact Dushyant Sahani, M.D., Abdominal and Interventional Radiology, at 671-726-3937.
We would also like to thank Carlos Fernàndez del Castillo, M.D.,
Gastrointestinal Surgery, and William R. Brugge, M.D., Gastrointestinal
Unit, for their assistance and advice for this issue.
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References
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Brugge, WR, Lauwers, GY, Sahani, D, Fernandez-del Castillo, C and Warshaw, AL. (2004) Cystic neoplasms of the pancreas. N Engl J Med 351: 1218-26
Brugge, WR. (2005) Should all pancreatic cystic lesions be resected?
Cyst-fluid analysis in the differential diagnosis of pancreatic cystic
lesions: a meta-analysis. Gastrointest Endosc 62: 390-1
Brugge, WR, Lewandrowski, K, Lee-Lewandrowski, E, Centeno, BA, et al.
(2004) Diagnosis of pancreatic cystic neoplasms: a report of the
cooperative pancreatic cyst study. Gastroenterology 126: 1330-6
Kawai M, Uchiyama K, Tani M, Onishi H, Kinoshita H, Ueno M, Hama T,
Yamaue H. (2004) Clinicopathological features of malignant intraductal
papillary mucinous tumors of the pancreas: the differential diagnosis
from benign entities. Arch Surg. 139:188-92.
Sahani, DV, Kadavigere, R, Saokar, A, Fernandez-del Castillo, C, et al.
(2005) Cystic pancreatic lesions: a simple imaging-based classification
system for guiding management. Radiographics 25: 1471-84
Sahani, DV, Saokar, A, Brugge, W., Fernandez-del Castillo, C, and Hahn, P. (2006). Small (<3 centimeters) pancreatic cysts – how aggressive should we be? Radiology (in press)
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