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436 3 HEPATOBILIARY AND PANCREAS CANCER
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21 MANAGEMENT OF INTRAHEPATIC AND EXTRAHEPATIC CHOLANGIOCARCINOMA 437
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22 Management of Cystic Neoplasms of
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the Pancreas
Umar Hayat1, Mahnur Haider2, Brooke Glessing1 & Amitabh Chak
1
Division of Gastroenterology and Hepatology, University Hospitals Cleveland Medical Center, Cleveland, Ohio, USA
2
Department of Hepatology, Cleveland Clinic, Cleveland, Ohio, USA
Introduction
Pancreatic cystic neoplasms (PCN) encompass a large spectrum of benign, premalignant, and malignant cysts. They are being diagnosed with increasing frequency due to the widespread use of cross-sectional imaging often during work-up for unre­lated medical problems (Gardner etal. 2013). The overall risk of a PCN being malignant is low, at less than 0.1% (Scheiman etal. 2015). Despite the increased detection of PCNs, the inci­dence of pancreatic cancer has remained relatively stable yet there has been a 189% increase in pancreatectomies over the last two decades. Therefore, the tremendous clinical vari­ability of pancreatic cysts presents a significant diagnostic and therapeutic challenge to clinicians. A key component of clinical management of these cysts is to accurately identify the small percentage of cysts with early invasive cancer or high-grade dysplasia and to predict which will develop cancer in the future so as to avoid both missing detection of early cancer and refer­ring for unnecessary surgical intervention (Klibansky et al. 2012; Yoon etal. 2021).
The estimated prevalence of asymptomatic pancreatic cystic neoplasms (PCNs) in the general population is 2.5–15%. Studies have reported high variability in the prevalence of PCNs depend­ing on the imaging modality used, ranging from 2.4% to 44% on magnetic resonance imaging (MRI), to 3% on computed tomog­raphy (de Jong etal. 2010; Falqueto etal. 2018; Girometti etal. 2011; Laffan etal. 2008). In one of the largest, population-based studies looking at 25,300 healthy individuals who had an abdominal CT as a part of a health screening exam, the age and sex-adjusted prev­alence of PCNs was 2.2% (Chang etal. 2016). In a meta-analysis of 17 studies that included CT and MRI, the global pooled preva­lence of PCNs was 8% with the highest prevalence reported in the Americas and in older persons (Zerboni etal. 2019).
Age has been strongly associated with PCN prevalence and it is estimated that 10% of people above 70 years have a pancreatic cyst (Elta etal. 2018). A six-fold increase in the rate of detection has
Gastrointestinal Oncology: A Critical Multidisciplinary Team Approach,
Second Edition. Edited by Janusz A. Z. Jankowski. © 2024 John Wiley & Sons Ltd. Published 2024 by John Wiley & Sons Ltd.
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been observed in persons in their eighth decade of life compared to those in their fourth decade of life (Gardner et al. 2013). Moreover, the prevalence, number, and size of cysts have been shown to increase with age. After five years of follow up of partic­ipants (mean age of 60.52 years) with PCNs, 30.8% had an increase in size and number of cysts, 24.1% had no change and
1.3% had a reduction in cyst size and number (Kromrey et al.
2018). No difference in prevalence of PCNs by sex have been observed (de Jong etal. 2010; Girometti etal. 2011; Kromrey etal. 2018; Laffan etal. 2008).
The cause of concern when a PCN is detected is the potential for malignant transformation. While the overall risk of malig­nant transformation for all PCNs remains low (Elta etal. 2018), the risk becomes clinically relevant in mucin producing cystic neoplasms such as intraductal papillary mucinous neoplasm (IPMNs) or mucinous cystic neoplasms (MCNs). In a popula­tion-based, cross-sectional analysis comparing the prevalence of mucin-producing adenocarcinomas from the Surveillance Epidemiology and End Results (SEER-18) data to the esti­mated prevalence of PCNs in the US, the calculated preva­lence rate for malignant transformation was rare at 33.2 per 100,000 people (Gardner etal. 2013). However, retrospective studies based on surgical series have estimated a much higher rate of malignancy with a pooled estimate of 15% in resected cysts from an analysis of 1296 patients (Scheiman etal. 2015). In another analysis of 3980 patients with suspected IPMNs, the risk of cancer was reported to be low at 2.8% (Scheiman etal.
2015) but other studies have shown contradictory results. In a systematic review of 99 studies, 42% of the resected IPMNs had either high-grade dysplasia or pancreatic cancer (Scheiman et al. 2015). This significant variability in the reported risk of malignant transformation of PCNs as detailed above is likely due to a large selection bias in these surgical case series and is overestimated which continues to make management decisions challenging. Furthermore, no existing test can identify the type of PCN pre-operatively with a high accu­racy. Several guidelines (2015 American Gastroenterological Association [AGA] (Vege etal. 2015), 2016 American Society of Gastrointestinal Endoscopy [ASGE] (Committee, A.S.o.P.
438
22 MANAGEMENT OF CYSTIC NEOPLASMS OF THE PANCREAS 439
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et al. 2016), 2017 Fukuoka guidelines by International Association of Pancreatology [IAP] (Tanaka etal. 2017), 2018 American College of Gastroenterology [ACG] (Elta et al.
2018), 2018 European Study Group, and American College of Radiology (Elta etal. 2018)) have attempted to risk stratify the PCNs by identifying features that are predictive of harboring malignancy and thus minimizing diagnostic uncertainty that can lead to clinically significant errors for our patients. These features are discussed in detail later in the chapter (Elta etal. 2018; European Study Group on Cystic Tumours of the, P. 2018; Scheiman etal. 2015; Tanaka etal. 2017).
PCNs can be broadly classified as neoplastic versus non-neo­plastic and mucin producing versus non-mucin producing. These can be differentiated by cross-sectional imaging and endoscopic ultrasound (EUS) with or without cyst fluid and cyst wall lining analysis though the accuracy of the currently available diagnostic tools to identify the type of PCN remains subpar with advancements in the fields of radiology and endo­sonography expected to continue to improve upon it (Elta etal.
2018). This chapter will highlight the various types of PCNs (Table 1) and their management but will predominantly focus on the diagnostic and therapeutic management of the mucin producing cystic neoplasms (specifically IPMNs).
Neoplastic and Mucin Producing Pancreatic Cystic Neoplasms
Intraductal Papillary Mucinous Neoplasms
An intraductal papillary mucinous neoplasm (IPMN) can be diagnosed on imaging and is typically connected to the main pancreatic duct; this differentiates IPMNs from mucinous cystic neoplasms (Scheiman et al. 2015). They can be classified by location: side-branch, main duct, or mixed (a combination of side branch and main duct). A branch duct IPMN (BD-IPMN) is the most common PCN and has the lowest risk of harboring high-grade dysplasia and/or invasive cancer (Goh et al. 2014; Nguyen etal. 2015; Sahora etal. 2013). Although some patients with BD-IPMNs warrant consideration for surgical resection, most are incidentally discovered in elderly patients where sur­veillance is a better option considering the risks associated with surgery and a low annual rate of progression [1.4–6.9%] (Lafemina etal. 2013; Malleo etal. 2015). Mixed and main duct IPMNs are less common but have a higher risk for malignancy with 38–68% of resected main duct IPMNs found to have high-grade dysplasia and/or pancreatic cancer (Elta etal. 2018). Therefore, surgical resection of all IPMNs with suspected main duct involvement is recommended. One interesting endoscopic feature of an MD-IPMN is a fish-eye papilla where a patulous, mucin extruding pancreatic orifice which is visible during duo­denoscopy in 20% to 55% of the cases and is more often noted in malignant disease (Elta etal. 2018; Kitagawa etal. 2003; Maire etal. 2003) (Figure 1).
Of note, patients with IPMNs are suspected to have a “field defect” where all ductal epithelial cells in the pancreas are sus­pected to be at risk for dysplastic change and malignancy. This may be why up to 40% of the patients present with multifocal BD-IPMNs (Rodriguez etal. 2007; Waters etal. 2008) though the cumulative risk of high-grade dysplasia or invasive cancer does not seem to be higher (Tanaka et al. 2017). This is also why it has been noted that patients with BD-IPMNs have an increased risk (around 2–4%) of developing “concomitant” pancreatic adenocarcinoma (PDAC) in an anatomically differ­ent area in the pancreatic parenchyma independent to the risk of malignant transformation within the IPMN itself (Maguchi et al. 2011; Tanno etal. 2010). This not only underlines the importance of evaluating the entire pancreas at the time of cyst evaluation but also the need to continue surveillance in the pancreatic remnant after surgical resection of a BD-IPMN or a main duct IPMN. Diagnostic techniques and management of BD-IPMNs is discussed later in the chapter.
Mucinous Cystic Neoplasms
Mucinous cystic neoplasms (MCNs) are primarily found in middle aged women in the body or tail of the pancreas. Radiographically, MCNs are round, can be unilocular or multi­locular and usually have thick cyst walls. They usually do not communicate with the pancreatic duct and occasionally can have peripheral “eggshell” calcification which is considered a pathognomic feature for MCNs. Histologically, they are dis­tinct from other types of PCNs as they have columnar epithe­lium surrounded by ovarian stroma. They do have a risk of malignant transformation and in an analysis of resected MCNs high-grade dysplasia or pancreatic cancer, it was demonstrated to be around 10% (Park etal. 2014) though the risk is negligible in MCNs that are smaller than 3 cm in size and have no other concerning radiological characteristics (Goh etal. 2006).
Neoplastic and Non-Mucin Producing Pancreatic Cystic Neoplasms
Serous Cystadenoma
Serous cystadenomas (SCAs) commonly occur in women in their 50s and 60s. They can have three characteristic morpho­logic appearances on imaging including polycystic, microcys­tic, or honey combing and oligo-cystic. BD-IPMNs can be differentiated from SCAs based on imaging if the SCA is poly­cystic or microcystic but this can be challenging if the SCA is oligo-cystic. Another imaging characteristic associated with SCAs is a central calcified scar that can be seen in less than half of these PCNs (Figure 2). The reason why it can be impor­tant to differentiate these from mucin producing PCNs is that the risk of malignancy is very low (0.1%) in SCAs and thus surveillance is not generally required. Even though most of these are asymptomatic, occasionally they can cause
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ductal adenocarcinoma
Jaundice is a clinical feature associated with
testing is recommended in
patients presenting with
obstructive jaundice worrisome
Surgical resection without further
considered a
Not discussed Presence of jaundice is
features
high-risk feature
and EUS±FNA and/
or a multidisciplinary
evaluation is
recommended
associated with pseudocysts and IPMNs
History of pancreatitis a clinical feature
evaluation and consider surgery
Recommend EUS for further
to cyst is considered
evaluation
MPD dilation warrants EUS/FNA
for symptom relief
a “worrisome feature”.≥10mm
dilation is considered a
“high-risk stigma” and surgical
Dilation of 5–9mm is considered
high-risk
considered a
>5mm dilation is
feature
Considered a high-risk
resection is recommended
high-risk feature
and EUS±FNA and/
or a multidisciplinary
evaluation is
recommended
evaluation
Presence of a mural nodule warrants EUS/FNA
and an evaluation with EUS is
recommended
Considered a “worrisome feature”
considered a
high-risk feature
and EUS±FNA and/
or a multidisciplinary
evaluation is
Not discussed Mural nodule
FNA
≥3 cm cyst size warrant EUS/
symptoms follow up is
recommended. For cysts >
5mm dedicated imaging is
For cysts < 5mm and no
recommended
considered a
≥3 cm cyst size
considered a high-risk
≥3 cm cyst size
recommended for
high-risk feature
and EUS±FNA and/
or a multidisciplinary
feature
Not discussed
“worrisome feature” and EUS is
Pancreatic atrophy is considered a
considered a
recommended
high-risk feature and
EUS±FNA and/or a
characterization of cyst
evaluation is
recommended
multidisciplinary
evaluation is
recommended
is considered
predictive of
malignancy and
should be
evaluated
Jaundice Presence of jaundice
European AGA ACG IAP ASGE
Pancreatitis Not discussed Not discussed Pancreatitis secondary
PD dilation ≥10mm dilation is M
Imaging
predictive of
malignancy
characteristics

malignancy
Mural Nodule ≥5mm predictive of
≥40mm associated
with cancer
Cyst size cyst diameter
Not discussed Not discussed Upstream atrophy
Pancreatic
atrophy
https://t.me/medicina_free
every 2 years if no
change
in 6 months, then
for 1 year, then
yearly for 2 years
CT / MRI for 6 months
Not discussed
and then every 2
years if stable
EUS in 3-6 months,
followed by
alternating MRI with
EUS every year. Can
consider surgery in
young patients
alternating with
3-6 months. Should
consider surgery in
young patients
Not discussed
and EUS is recommended
Considered a “worrisome feature”
elevated CA19-9 are
not found, then a
Not discussed If benign causes of
2-3 cm MRI or EUS every 6–12 2-3
cm
multidisciplinary group MRI with EUS every
>3cm Referral to >3cm Close surveillance
examination
with EUS-FNA
Recommend
months for 3 years
>3
cm
and MRI alternating with
EUS every 6 months for 3 years
cm
Not discussed Not discussed
concerning symptom
and EUS or MRI
multidisciplinary
evaluation should be
pursued
Not discussed Considered a
should be considered
< 1cm MRI every 2 years for 4years < 1cm CT / MRI
surveillance in 1
MRI for
cm
< 3
every 2 years for
a total of 5 years
if there is no
change in size or
characteristics
when there is
concern for
malignancy
European AGA ACG IAP ASGE
Serum Based CA 19-9 Can be considered
surgery
Relative indication for
Diabetes
New-onset
CA19-9, MRI and/
Clinical evaluation,
diagnosis
Surveillance First year of
or EUS every 6
months
year and then
1-2 cm MRI every year for 3 years 1-2
CA19-9, MRI and/
or EUS every year
Clinical evaluation,
year of
diagnosis
After the first
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Table 1 Characteristic and epidemiology of different pancreatic cystic neoplasms.
Characteristic MCN BD-IPMN SCA SPN
Sex (% Female) >95% ~ 55% ~70% Females> males
Age (decade) 4th, 5th (“Mother”) 6th, 7th 6th, 7th (“Grandmother”) 2nd, 3rd
Asymptomatic ~ 50% Mostly when small ~ 50% ~ 50%
Location (% body/tail) 95% 30% 50% Predominantly
Common capsule Yes No Ye s Yes
Calcification Rare, curvilinear in the cyst
wall
Gross appearance Orange Grape-like Spongy/honeycomb like Round, soft, encapsulated
Multifocality No Yes No Solid and cystic
Internal structure Cysts in cyst Cyst by cyst Microcystic and/or
Main PD communication Infrequent Ye s No No
Overall risk of malignancy/
HGD
Aspirate characteristic Viscous Viscous, or thin Thin, often bloody Bloody
Cytology Findings Columnar cells with
CEA levels > 200 ng/ml in ~75% < 5 – 20 ng/ml > 200 ng/ml in ~75% Insufficient data
~10% ~7% in 10 yrs (low risk),
variable atypia, Stain mucin < 50%
No 30–40%, central Occasional
hemorrhagic mass
components
Unilocular
macrocystic
0.10% ~ 10%
~24% in 10 yrs (high risk)
Cuboidal cells +ve for
glycogen (< 50%)
Columnar cells with
variable atypia, Stain mucin < 50%
Branching papillae with
myxoid stroma (high yield from solid component)
Figure 1 Main duct IPMN with a gaping papilla which is extruding mucus.
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symptoms such as pancreatitis or obstructive jaundice when they enlarge, especially if located in the head of the pancreas, in which case surgical resection can be considered (Elta etal. 2018; Jais etal. 2016).
Solid Pseudopapillary Neoplasms
Solid pseudopapillary neoplasms (SPNs) are rare and are more commonly found in young women in their 20s. Radiographically, SPNs have solid growth with cystic degeneration with both solid and cystic areas noted on imaging. The age at detection is highly variable ranging from childhood to adulthood and can be found in any part of the pancreas. Even though about 10% of SPNs can be aggressive tumors they have a better prognosis than pancreatic adenocarcinoma with a 5-year disease-specific survival of 98% (Elta etal. 2018). A referral to a high-volume pancreatic center for surgical resection is recommended for all patients with SPNs.
Cystic Pancreatic Neuroendocrine Tumors
Pancreatic neuroendocrine tumors (pNETs) are rare tumors that usually presents in the 60s. They are non-secreting tumors and morphologically can be solid, cystic, or mixed (Elta etal.
2018). The management of these lesions is not discussed and is out of the scope of this chapter.
Non-Neoplastic and Non-Mucin Producing Pancreatic Cysts
Pseudocysts
Pseudocysts are usually found in patients with a history of pan­creatitis. They are less common than PCNs but it is important to differentiate between them because pseudocysts do not have a malignant potential and thus do not require surveillance or inter­vention if asymptomatic. Additionally, if symptomatic, pseudo­cysts can be treated with endoscopic drainage alone whereas PCNs may require surgery and are not treated with endoscopic drainage. Cystic lesions in the pancreas are suspected to be a pseudocyst in patients with a prior history of pancreatitis whose cystic lesion develops on imaging after the episode of pancreatitis. In individuals with idiopathic pancreatitis over the age of 40, an underlying PCN as a cause of pancreatitis if the cystic lesion is seen on initial imaging should be strongly considered prior to labeling the cystic lesion as a pseudocyst (Elta etal. 2018).
Epidemiology of PCNs
The evolving fields of radiology and endosonography have improved the diagnostic ability to differentiate different types of PCNs but this should not overshadow the importance of several epidemiological factors that can provide useful hints toward the
diagnosis. Factors such as gender, age of diagnosis, and location of the cystic lesion in the pancreas can all be used in solving the diagnostic dilemma of PCNs as detailed in Table 1.
Clinical Presentation of PCNs
Majority of PCNs are discovered incidentally in asymptomatic individuals in clinical practice but retrospective surgical case series have reported symptoms in as high as 80% of individuals with PCNs (Parra-Herran etal. 2010; Walsh etal. 2002). This high percentage is likely a result of selection and referral bias since other observational studies show the prevalence of symp­toms to be much lower around ~20% (Crippa et al. 2017; Mukewar etal. 2017). Of note, symptomatic IPMNs have been noted to have an association with malignancy (OR 1.6 CI 1.0-
2.6) (Anand etal. 2013). A myriad of gastrointestinal symp­toms has been reported to have an association with PCNs in surgical case series [abdominal pain (69%), weight loss (38%), back pain (18%), palpable mass (5%), and postprandial fullness (4%)] but it is extremely difficult to attribute these to the PCNs due to the non-specific nature of these symptoms. On the con­trary, pancreatitis (36%) and obstructive jaundice (18%) can more directly be attributable to PCNs. It is especially important to consider a PCN as the cause of pancreatitis and not misdiag­nose it as a pseudocyst in patients presenting with pancreatitis above the age of 40. Furthermore, PCN related acute pancrea­titis and obstructive jaundice can both be an indicator of advanced neoplasia within the PCN (or indicator that the PCN is harboring advanced neoplasia) (Del Chiaro et al. 2013; Rivera etal. 1997; Shin etal. 2010; Vege etal. 2015). Therefore, lesion related obstructive jaundice is considered an absolute criterion for surgery and lesion related acute pancreatitis is considered a “worrisome feature” and a relative indication for surgery (Tanaka etal. 2017, 2012). New-onset diabetes is also a concern in patients with IPMNs above the age of 50 since these patients are noted to have an increased risk of high-grade dys­plasia or pancreatic cancer and thus a thorough evaluation is warranted with an MRI /MRCP and/or EUS (Leal et al. 2015; Mimura etal. 2010).
Diagnostic Tools for PCNs
Radiology
Cross-sectional imaging serves a dual purpose in the diagnostic evaluation of a PCN. It helps characterize the type of PCN and assesses for presence of high-grade dysplasia and/or pancreatic cancer. Different retrospective studies have shown variable rates of diagnostic accuracy of the contrast enhanced computed tomography (CECT) scans and Magnetic Resonance Imaging (MRI)/Magnetic Resonance Cholangiopancreatography (MRCP) in identifying the type of PCN as well as differentiating between
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benign and malignant cystic lesions. In a systematic review of 19 studies, CT can accurately pick up benign from malignant PCNs in 70–80% of the cases with a sensitivity of 80% for IPMNs. MRI/ MRCP had a similar accuracy for differentiating a benign from a malignant PCN ranging from 55–76% though had a much higher sensitivity of around 96% for diagnosing IPMN (Jang etal. 2015; Jones etal. 2013; Lee etal. 2011).
MRI/MRCP is preferred over CT due to its lack of radiation and a higher sensitivity for identification of cyst communica­tion with the pancreatic duct (that likely explains its higher accuracy for diagnosing a BD-IPMN), for detecting presence of a solid component within the cystic lesion and for identification of multifocal PCNs (Sahani etal. 2013; Waters et al. 2008). Despite its many advantages, MRI/MRCPs do have some cons including lower spatial resolution, decreased sensitivity for detecting calcification within the cystic lesion, longer imaging duration, and increased susceptibility to motion artifact. Secretin enhanced MRCP can improve the visualization of the pancreatic duct and detect communica­tion between the pancreatic duct and the PCN when it would not be obvious otherwise though the small incremental benefit in the diagnostic yield is a questionable justification at this time for the higher cost associated with secretin use. The use of a combined approach with MRI or CT with EUS as discussed below or even Positron Emission Tomography with CT has also been suggested to increment the low diagnostic yield of single imaging modalities for differentiating benign from malignant PCNs. A small study has shown that PET combined with CT had a diagnostic yield of around 94% in this scenario as compared to 77% for CT and 86% for MRI with MRCP (Kauhanen etal. 2015).
Endoscopic retrograde cholangiopancreatography (ERCP) may have a limited role in evaluation of a MD-IPMN. The use of ERCP in routine evaluation of PCNs remains limited though due to its invasive nature and high risk of complications and cross-sectional imaging along with EUS remain the mainstay for diagnostic management of PCNs.
Endoscopic Ultrasound
Endoscopic Ultrasound (EUS) is an extremely useful tool that aids in the diagnosis of PCNs not only as a stand along imaging technique but also via sampling of the cyst fluid and its analysis. Cyst fluid analysis increases the diagnostic yield and can espe­cially help in the differentiation between mucin producing and non-mucin producing PCNs. EUS imaging alone (without cyst fluid analysis) is accurate in 65–96% of the cases when differen­tiating benign from a malignant PCN. This is similar to the accuracy of the MRI and the CT noted above and though EUS alone adds only a limited incremental value over cross-sectional imaging, it does have a higher resolution and has been demon­strated to have a higher sensitivity for identification of a mural nodule (MN) within a PCN. The mural nodule has irregular borders on EUS and usually has a hyperechoic center as opposed to a mucin ball which has a smoother wall with a hyperechoic rim and hypoechoic center (Tirkes etal. 2014). Additionally, an EUS without features of concern in a PCN has a high negative predictive value for ruling out malignancy (Scheiman et al.
2015). Despite several advantages, EUS should be used judi­ciously in the diagnostic management of PCNs due to its inva­sive nature when CT/MRI are not sufficiently diagnostic or there are cystic features of concern on cross-sectional imaging warranting further evaluation (European Study Group on Cystic Tumours of the, P. 2018; Harima etal. 2015; Tanaka etal. 2017).
Adverse events are reports in 2.7% to 5% of the cases under­going EUS-FNA (Wang KX Assessment 2011). Most common adverse events include abdominal pain, pancreatitis and intra­cystic hemorrhage (Al-Haddad et al. 2008; Lee et al. 2005; Tarantino etal. 2014; Varadarajulu and Eloubeidi 2004). Cyst infection rates of as high as 14% have also been quoted in older studies (Wiersema etal. 1997) though more recent data has shown much lower rates of less than 1% (Guarner-Argente etal. 2011). The current ASGE guidelines suggest consideration of prophylactic antibiotics when performing EUS-FNA in PCNs, but this practice remains variable in the real world (Committee, A.S.o.P. etal. 2016).
Radiomics
Radiomics is the analysis of mathematically derived textural fea­tures from cross-sectional imaging that are not perceptible to human eyes. Multiple studies in radiomics have employed vari­able extraction of radiometric data from CECTs via machine learning algorithms with some combining radiomics, cyst mor­phology and clinical features to differentiate types of PCNs (Dmitriev etal. 2017; Xie etal. 2020; Yang etal. 2019) and more recently, risk stratify IPMNs (Attiyeh etal. 2019; Hanania etal. 2016; Hoffman etal. 2017). While radiomics is an exciting tool in the arsenal for classification and risk stratification of PCNs, its use has largely been limited to clinical trials at large academic centers and is several years away from prime-time utilization.
Cytology, Biomarkers, and Molecular Analysis
EUS-guided fine-needle aspiration (FNA) of the pancreatic cystic fluid is considered when additional diagnostic information is warranted such as in patients being considered for surgery or in patients where a diagnosis of a serous cyst would help avoid surveillance. The cyst fluid obtained via FNA can be sent for biochemical, cytological, and molecular analysis. This can be very useful in trying to distinguish mucin producing from non­mucin producing PCNs and avoid unnecessary surveillance.
Even though cytology of the cyst fluid is highly specific (83–100%), it has been shown to lack sensitivity for diag­nosing PCNs (27–48%) and thus has a low diagnostic accuracy (8–59%) (Stelow etal. 2003; Thosani etal. 2010; Wang etal.
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2015). The lack of sensitivity is likely a result of a low number of intact exfoliated cells that are usually detected in the sample.
The analysis for fluid CEA and amylase levels is also useful when distinguishing mucinous from non-mucinous PCNs but these will not differentiate MCNs and IPMNs. A cutoff value of ≥192–200 ng/mL has previously been noted to have 79% accu­racy in diagnosis of mucinous cysts (Brugge etal. 2004) but more recent studies have shown a lower sensitivity and speci­ficity (63% and 88% respectively) that can lead to a misdiag­nosis of around ~40% of mucinous cysts (Thornton etal. 2013). Additionally, higher CEA levels have not shown to correlate with risk of high-grade dysplasia and/or invasive cancer in PCNs (Brugge etal. 2004; Park etal. 2011). Cyst fluid amylase levels are mostly helpful in excluding pseudocysts when they are low but high amylase levels have limited diagnostic utility as they can be elevated in IPMNs, pseudocysts and in rare instances, MCNs as well (Ngamruengphong and Lennon 2016; Thornton etal. 2013).
Intra-cystic glucose levels have recently gained traction as a low-cost diagnostic test with many studies now showing that intra-cystic glucose levels are superior to CEA levels in differ­entiating mucinous from non-mucinous PCNs. Mucinous PCNs are expected to have low glucose levels partly due to the metabolism from the active neoplastic cells. Intra-cystic glucose concentration < 50 mg/dL has significantly better sen­sitivity than a CEA level > 192 ng/mL for diagnosing mucinous cysts (93.6% vs 54.8%) (Ribaldone etal. 2020). A meta-analysis of 8 studies with included 609 PCNs showed pooled sensitiv­ities for glucose vs CEA of 91% vs 56% and pooled specificities for glucose vs CEA of 96% vs 86% (McCarty etal. 2021a).
Next-generation sequencing (NGS) allows evaluation of gene panels and whole exome in intact cell and cell-free nucleic acid present in the cyst fluid and can look for DNA mutations that are commonly associated with development of pancreatic adenocarcinoma (RAS, CDKN2A, SMAD4, PTEN, PIK3CA, and TP53). These can help with classification of mucinous versus non-mucinous PCNs as well as risk stratification of IPMNs. Presence of dual KRAS and GNAS mutations can diag­nose mucinous PCNs with an accuracy of 97% (McCarty etal. 2021b). Moreover, presence of TP53, PIK3CA, and/or PTEN mutation has 88% sensitivity and 95% specificity, respectively for diagnosing IPMNs with advanced neoplasia (Singhi et al.
2018). Even though cyst fluid molecular analysis by NGS has a high accuracy in identification of the type of PCN and risk stratification for advanced neoplasia, limited availability and high cost remain big deterrents for routine use. The clinical utility of these biomarkers remains to be demonstrated.
Advanced EUS Based Techniques for Evaluation of PCNs
EUS with and without cyst analysis remains a subpar test in guiding management decisions due to low cellularity and a suboptimal diagnostic accuracy of the biomarkers. Therefore,
several techniques have been developed for evaluation of cyst wall including tissue acquisition from the lining of the cyst wall for histology. Use of needle based confocal light endomicros­copy (nCLE) and through-the-needle intracystic biopsy (Moray micro forceps; US Endoscopy, Mentor, Ohio) are the tech­niques that have shown the most promise in increasing the diagnostic yield of EUS with an acceptable risk profile.
The microforceps biopsy (MFB) can be advanced through a 19G needle while performing EUS–FNA and allows for tissue sampling of the cyst wall. The technical success of the device in limited series is reported to be approximately 99% with a tissue acquisition yield of 88% and a diagnostic accuracy of 69% (Balaban etal. 2021). Adverse events are reported in around 9% of the cases and include intracystic hemorrhage, mild acute pancre­atitis, abdominal pain, and post-procedural infection (Balaban etal. 2021). While EUS–FNA with MFB allows for a high diag­nostic accuracy in management of PCNs, the higher risk of adverse events as compared to EUS–FNA alone is likely a deter­rent for incorporation of this technique in routine clinical practice.
EUS guided nCLE is another advanced technique that allows real-time in vivo endo-microscopic imaging of the intracys­tic epithelium of the cyst wall. Confocal images are obtained when a low-power laser illuminates the tissue after intravenous administration of fluorescent contrast agent (such as fluores­cein [CellVizio; Mauna KeaTechnologies, Paris, France]) and the reflected light is focused through a pinhole onto a detection system that transforms it to a detailed bitmap gray scale image on the computer (Neumann et al. 2010; Polglase et al. 2005). Studies have established the characteristic features of IPMNs (presence of villous structures), MCNs (a thick gray line), SCAs (a superficial vascular network pattern corresponding to a dense and subepithelial capillary vascularization only seen in SCAs), cystic neuroendocrine tumors (black neoplastic cell clusters with white fibrous areas) and pseudocysts (field of bright par­ticles) (Napoleon et al. 2015, 2016). nCLE can differentiate mucinous PCNs and non-mucinous PCNs with a diagnostic accuracy of around 89–99%. The pooled risk of post-procedure pancreatitis is around 1% (Facciorusso etal. 2020). In addition, several imaging variables in nCLE have been identified that determine the presence of advanced neoplasia in IPMNs with papillary epithelial thickness (width ≥ 50 μm) and papillary epi­thelial darkness (cut-off ≤ 90 pixel intensity) having the highest interobserver agreement for detection of advanced neoplasia (Krishna etal. 2020). Similarly, a nCLE pattern of dark aggre­gates of neoplastic cells correlated with the morphologic fea­tures of irregular branching and budding and was diagnostic of malignancy. The cost and unproven clinical utility have limited the widespread adoption of nCLE in clinical practice.
Contrast-enhanced EUS (CE-EUS) has been proposed to be useful in the presence of MNs or solid components to assess the presence of vascularization. Even though earlier studies did not report any improvement over traditional EUS at differentiating