The Diagnostic Dilemma of Malignant Biliary Strictures

diagnostics

Review The Diagnostic Dilemma of Malignant Biliary Strictures

Robert Dorrell 1 , Swati Pawa 2, Yi Zhou 3, Neeraj Lalwani 4 and Rishi Pawa 2,*

1 Department of Medicine, Wake Forest School of Medicine, Winston-Salem, NC 27157, USA; [email protected] 2 Division of Gastroenterology, Department of Medicine, Wake Forest School of Medicine, Winston-Salem, NC 27157, USA; [email protected] 3 Department of Pathology, Wake Forest School of Medicine, Winston-Salem, NC 27157, USA; [email protected] 4 Department of Radiology, Wake Forest School of Medicine, Winston-Salem, NC 27157, USA; [email protected] * Correspondence: [email protected]

Received: 31 March 2020; Accepted: 21 May 2020; Published: 25 May 2020

Abstract: The differential diagnosis for biliary strictures is broad. However, the likelihood of malignancy is high. Determining the etiology of a biliary stricture requires a comprehensive physical exam, laboratory evaluation, imaging, and ultimately tissue acquisition. Even then, definitive diagnosis is elusive, and many strictures remain indeterminant in origin. This literary review examines the diagnostic dilemma of biliary strictures and presents innovations in both histochemical and endoscopic techniques that have increased the diagnostic power of differentiating benign and malignant strictures. The field of tissue biopsy is revolutionizing with the advent of free DNA mutation profiling, fluorescence in situ hybridization (FISH), and methionyl t-RNA synthetase 1 (MARS 1), which allow for greater testing sensitivity. Endoscopic ultrasound, endoscopic retrograde cholangiopancreatography (ERCP), cholangioscopy, confocal laser endomicroscopy, and intraductal ultrasound build upon existing endoscopic technology to better characterize strictures that would otherwise be indeterminate in etiology. This review uses recent literature to insert innovative technology into the traditional framework of diagnostic methods for malignant biliary strictures.

Keywords: malignant biliary stricture; hepatobiliary malignancy; pancreatic cancer; endoscopic ultrasound; ﬁne-needle aspiration and biopsy; endoscopic retrograde cholangiopancreatography; cholangioscopy; intraductal ultrasound; confocal laser endomicroscopy

1. Introduction A biliary stricture is a narrowing of the biliary tree that can be caused by a myriad of etiologies, some benign, some life-threatening. There are three classes of biliary strictures: benign, malignant, and indeterminate. Unfortunately, only a minority of biliary strictures (15%–24%) are benign [1]. Diﬀerentiating between these benign and malignant strictures requires a complex diagnostic evaluation. Endoscopy is often vital to diagnosis through tissue sampling. However, recent advances in understanding and utilizing biomarkers are enhancing the diagnostic power of laboratory testing. This literary review attempts to present the diagnostic dilemma of identifying a stricture as malignant.

2. Etiology The most common cause of malignant stricture of the distal common bile duct is pancreatic adenocarcinoma. This occurs when the pancreatic tumor invades the common bile duct. Because

Diagnostics 2020, 10, 337; doi:10.3390/diagnostics10050337 www.mdpi.com/journal/diagnostics Diagnostics 2020, 10, 337 2 of 15 pancreatic cancer is often diagnosed at a later stage, 70% of patients with pancreatic cancer already have a biliary stricture at the time of diagnosis [2,3]. The second most common cause of malignant biliary stricture is cholangiocarcinoma, a primary tumor of the bile duct itself. A minority of cases are caused by other etiologies including primary duodenal adenocarcinoma, ampullary carcinoma, gallbladder carcinoma, hepatocellular carcinoma, lymphoproliferative disorders, and metastatic lesions [4]. Malignancies of the hepatopancreatic biliary (HPB) system are largely sporadic, but certain inﬂammatory conditions like primary sclerosing cholangitis, recurrent or chronic infections like cholangitis or pancreatitis, and even cholelithiasis are risk factors for developing a malignancy [5]. All biliary strictures should be taken seriously and evaluated thoroughly given the high chance of malignancy.

3. Presentation and Laboratory Markers The initial evaluation of biliary strictures includes physical exam and laboratory markers. Patients often present with malaise, weight loss, anorexia, jaundice, pruritis, nausea, and vomiting. These symptoms are generally associated with hyperbilirubinemia, which occurs due to the stricture’s blockage of bile excretion from the gallbladder to the small intestine [6]. As bilirubin levels rise, the symptoms typically progress surreptitiously until they have a major impact on the patient’s quality of life. More advanced obstructions can cause more fulminant symptoms secondary to infections like ascending cholangitis or hepatic abscesses [6]. Patients presenting with any of the symptoms over this wide spectrum should be examined for icterus as well as hepatosplenomegaly and lymphadenopathy. In turn, laboratory tests should include bilirubin levels as well as other markers of hepatobiliary dysfunction including aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), and gamma-glutamyl transferase (GGT). The greater the bilirubin level, the more likely that the stricture is malignant [7]. The abnormal liver biochemistry also follows the typical obstructive pattern, with ALP rising more than AST [8]. Furthermore, Thomasset et al. studied the relationship between initial laboratory results and the ultimate diagnosis of biliary stricture etiology. Based on their assessment of 830 patients with presumed biliary strictures, normal liver function tests (LFTs) help to rule out primary HPB malignancies. However, abnormal LFTs, even in the presence of normal bilirubin levels, were associated with a higher likelihood of malignant stricture. Therefore, isolated or combined abnormalities of bilirubin and LFTs confer a greater risk that a biliary stricture is malignant [9].

4. Biomarkers While standard laboratory tests can be somewhat helpful in determining etiology, more specific tests like biomarkers give better insight into the absence or presence of HPB malignancy causing stricture. The most commonly used tumor marker in this setting is cancer antigen 19-9 (CA 19-9), which is a carbohydrate antigen expressed on the surface of certain cancer cells [10,11]. The antigen sheds from these cell surfaces attached to various carrier proteins and can be detected in the bloodstream. CA 19-9 is typically associated with pancreatic cancer, but it can also be elevated with cholangiocarcinoma, cholestasis, cholangitis, cirrhosis, pancreatitis, and any cause of biliary obstruction [11–13]. Therefore, this marker cannot be used to reliably determine the etiology of a biliary stricture. Recent CA 19-9 research has focused on using the biomarker to better differentiate between malignant and benign processes of biliary obstruction. For example, Yue et al. measured CA 19-9 in conjunction with certain carrier proteins. The carrier proteins seem to be more specific to the organ of origin and can help to focus the differential of elevated CA 19-9 [12]. Other studies have shown that CA 19-9 levels are higher in malignant processes compared to benign. Therefore, a higher cutoff value for CA 19-9 decreases sensitivity, but increases specificity for malignant processes [14–16]. La Greca et al. also proposed correcting CA 19-9 levels for the presence of biliary obstruction and inflammation by calculating the CA 19-9 to total bilirubin ratio and CA 19-9 to CRP (C reactive protein) ratio, respectively. This study found that using ratios compared to CA 19-9 alone decreased the sensitivity, but improved Diagnostics 2020, 10, x FOR PEER REVIEW 3 of 14

Greca et al. also proposed correcting CA 19-9 levels for the presence of biliary obstruction and inflammation by calculating the CA 19-9 to total bilirubin ratio and CA 19-9 to CRP (C reactive protein) ratio, respectively. This study found that using ratios compared to CA 19-9 alone decreased Diagnosticsthe sensitivity,2020, 10 ,but 337 improved the specificity for malignant biliary obstruction [15]. While Liu 3et of al. 15 only found a mild improvement in specificity using the CA 19-9/bilirubin ratio (83%) compared to theCA specificity19-9 levels for alone malignant (81%), this biliary study obstruction also reported [15]. Whileon the Liu effects et al. of only CA found19-9 levels a mild plus improvement the CA 19- in9/bilirubin specificity ratio. using The the combination CA 19-9/bilirubin of the ratiotwo valu (83%)es compared compared to to CA CA 19-9 19-9 levels alone alone decreased (81%), sensitivity this study alsoto 62%, reported but increased on the e ffspecificityects of CA from 19-9 81% levels to 93% plus and the CAincreased 19-9/bilirubin diagnostic ratio. accuracy The combination from 74% to of 81% the two[17]. valuesAs the compared scope of CA to CA 19-9 19-9 testing alone broadens decreased an sensitivityd is better to understood 62%, but increased in the context specificity of biliary from 81%obstruction to 93% andand increasedinflammation, diagnostic this tumor accuracy marker from 74%may tobecome 81% [17 a]. mo Asre the reliable scope ofindicator CA 19-9 of testing HPB broadensmalignancies and in is betterthe future. understood in the context of biliary obstruction and inflammation, this tumor markerCarcinoembryonic may become a more antigen reliable (CEA) indicator is similar of HPB to CA malignancies 19-9, as it in is the a tumor future. marker that can be associatedCarcinoembryonic with a wide range antigen of pathologies. (CEA) is similar However, to CA the 19-9, utilization as it is of a CEA tumor at markerpresent thatis even can less be associatedgiven its low with sensitivity a wide range (30%–68%) of pathologies. and specificity However, (75%–95%) the utilization for cholangiocarcinoma of CEA at present [12]. is even less given its low sensitivity (30%–68%) and specificity (75%–95%) for cholangiocarcinoma [12]. 5. Non-Invasive Imaging Studies 5. Non-Invasive Imaging Studies Imaging studies play an essential role in the visualization, classification, and surgical planning of biliaryImaging strictures. studies playThe angoal essential of imaging role in is the to visualization, first assess classification,for dilation of and the surgical intrahepatic planning and of biliaryextrahepatic strictures. biliary The tree. goal Different of imaging modalities is to first have assess established for dilation different of the intrahepatic cutoff values and for extrahepatic pathologic biliarydilation tree. of the Di commonfferent modalities bile duct have(CBD) established and intrahepatic different bile cuto ducts.ff values The second for pathologic goal is to dilation pinpoint of the level common of obstruction. bile duct (CBD) This location and intrahepatic is typically bile described ducts. using The second the Bismuth–Corlette goal is to pinpoint classification the level ofsystem obstruction. (Figure 1), This which location groups is typically biliary strictures described into using fourthe different Bismuth–Corlette types depending classification on their location system (Figurealong the1), whichbiliary groups tree. Ancillary biliary strictures imaging into findings four di ffincludeerent types characteristics depending of on the their duct location walls along like thethickness biliary and tree. texture Ancillary [6,18]. imaging Imaging findings can be include broken characteristics into two categories: of the duct non-invasive walls like thicknessand invasive. and textureIn the algorithm [6,18]. Imaging of evaluating can be broken a malignant into two biliary categories: stricture, non-invasive non-invasive and imaging invasive. typically In the algorithm precedes ofinvasive evaluating imaging. a malignant biliary stricture, non-invasive imaging typically precedes invasive imaging.

Figure 1. The Bismuth–Corlette classificationclassification is a system for characterizing hilar strictures. Type I is limited toto the common hepatic duct,duct, below the main confluenceconfluence of the hepatic ducts. Type II involves the confluence of the left and right hepatic ducts. Type IIIa involves the main hepatic confluence and the confluence of the left and right hepatic ducts. Type IIIa involves the main hepatic confluence and extends to the bifurcation of the right hepatic duct. Type IIIb involves the main hepatic confluence extends to the bifurcation of the right hepatic duct. Type IIIb involves the main hepatic confluence and extends to the bifurcation of the left hepatic duct. Type IV involves the main, right, and left and extends to the bifurcation of the left hepatic duct. Type IV involves the main, right, and left hepatic confluence. hepatic confluence. Non-invasive imaging modalities of biliary strictures include right upper quadrant abdominal ultrasound (RUQUS), computed tomography (CT), contrast-enhanced magnetic resonance imaging (MRI) and magnetic resonance cholangiopancreatography (MRCP). RUQUS visualizes the liver, gallbladder, biliary tract, and pancreas and is often the first tool providers reach for when a patient Diagnostics 2020, 10, x FOR PEER REVIEW 4 of 14

Non-invasive imaging modalities of biliary strictures include right upper quadrant abdominal ultrasoundDiagnostics 2020 (RUQUS),, 10, x FOR PEER computed REVIEW tomography (CT), contrast-enhanced magnetic resonance4 of imaging 14 (MRI) and magnetic resonance cholangiopancreatography (MRCP). RUQUS visualizes the liver, Non-invasive imaging modalities of biliary strictures include right upper quadrant abdominal Diagnosticsgallbladder,2020 ,biliary10, 337 tract, and pancreas and is often the first tool providers reach for when a patient4 of 15 ultrasound (RUQUS), computed tomography (CT), contrast-enhanced magnetic resonance imaging presents with symptoms of obstructive jaundice. The benefits of RUQUS include low cost, lack of (MRI) and magnetic resonance cholangiopancreatography (MRCP). RUQUS visualizes the liver, radiation, and high sensitivity to detect biliary dilation or obstruction, with an accuracy of more than gallbladder, biliary tract, and pancreas and is often the first tool providers reach for when a patient presents90%. The with limitations symptoms of this of obstructive imaging modality jaundice. include The benefits poor ofvisualization RUQUS include of strictures low cost, in lackobese of radiation,presents with and symptoms high sensitivity of obstru to detectctive jaundice. biliary dilation The benefits or obstruction, of RUQUS withinclude an accuracylow cost, oflack more of than patientsradiation, and and low high accuracy sensitivity in identifyingto detect biliary the dilationetiology or of obstruction, a biliary obstruction with an accuracy (30–70%) of more [19,20]. than 90%. The limitations of this imaging modality include poor visualization of strictures in obese patients 90%.Compared The limitations to RUQUS, of this MRCPimaging with modality contrast-enhanced include poor MRIvisualization is not as of limited strictures by inbody obese habitus, and low accuracy in identifying the etiology of a biliary obstruction (30–70%) [19,20]. obtainspatients a and more low detailed accuracy view in identifying of the biliary the etiology system, of aand biliary captures obstruction extra-biliary (30–70%) structures [19,20]. to give a broaderComparedCompared sense of to tothe RUQUS, RUQUS, stricture MRCP MRCP in context with with contrast-enhanced[21,22]. contrast-enhanced Its images MRI are MRI detailedis not is as not enoughlimited as limited byto determinebody by bodyhabitus, the habitus, level ofobtainsobtains biliary aa obstruction, moremore detailed with view view 98% of of thesensitivity the biliary biliary system, and system, specificity. and and captures captures MRCP extra-biliary with extra-biliary contrast-enhanced structures structures to give MRI to a give may a alsobroaderbroader differentiate sense of of the thebetween stricture stricture benign in context in context and [21,22]. malignant [21 ,It22s ].images Itsstrictures, images are detailed arewith detailed enough a sensitivity to enough determine of to38%–90% determinethe level and the a specificitylevelof biliary of biliary obstruction, of 70%–85%. obstruction, with It 98%can with sensitivityalso 98% help sensitivity and in thespecificity. andstaging specificity. MRCP of cholangiocarcinomas with MRCP contrast-enhanced with contrast-enhanced and MRI determining may MRI surgicalmayalso alsodifferentiate management differentiate between [23]. between benign MRCP benign and is preferred malignant and malignant over strictures, its strictures, invasive with a counterpart withsensitivity a sensitivity of endoscopic 38%–90% of 38%–90% and retrograde a and cholangiopancreatographyaspecificity specificity of of 70%–85%. 70%–85%. It can It(ERCP) can also also helpfor helpinitial in the in evaluation thestaging staging of of cholangiocarcinomas of biliary cholangiocarcinomas strictures due and to determiningfewer and determining side effects andsurgicalsurgical a similar managementmanagement ability to [23]. [visualize23]. MRCP MRCP the is ispreferred stricture preferred over[22–24] over its itsinvasive(Figure invasive 2).counterpart counterpart endoscopic endoscopic retrograde retrograde cholangiopancreatography (ERCP) for initial evaluation of biliary strictures due to fewer side effects cholangiopancreatography (ERCP) for initial evaluation of biliary strictures due to fewer side effects andand aa similarsimilar ability to to visualize visualize the the stricture stricture [22–24] [22–24 (Figure] (Figure 2). 2).

Figure 2. A,B: Axial contrast computed tomography (CT) shows enhancing intraductal polypoid mass Figure 2. (A,B): Axial contrast computed tomography (CT) shows enhancing intraductal polypoid consistentFigure 2. A ,Bwith: Axial intraductal contrast computed cholangiocarcinoma tomography (CT) (arrow); shows enhancing C: The intraductalcircle demonstrates polypoid mass a T2W massconsistent consistent with withintraductal intraductal cholangiocarcinoma cholangiocarcinoma (arrow); (arrow); C: The (C ):circle The demonstrates circle demonstrates a T2W a T2W hypointense lesion found on magnetic resonance cholangiopancreatography (MRCP); D: Postcontrast hypointensehypointense lesion found found on on magnetic magnetic re resonancesonance cholangiopancreatography cholangiopancreatography (MRCP); (MRCP); D: Postcontrast (D): Postcontrast MR showing an incidentally found subtle mural thickening of the gallbladder fundus later diagnosed MRMR showingshowing an an incidentally incidentally found found subtle subtle mural mural thic thickeningkening of the of gallbladder the gallbladder fundus fundus later diagnosed later diagnosed as synchronous gallbladder carcinoma. asas synchronoussynchronous gallbladder gallbladder carcinoma. carcinoma.

Contrast-enhancedContrast-enhanced CT CT CT scans scans scans are are are useful useful useful for for identi for identi identifyingfyingfying HPB HPB HPBmasses masses masses and delineatingand and delineating delineating the extent the the extent ofextent of massesofmasses masses byby byshowing showing tissuetissue tissue and and andvessel vessel vessel infiltration infiltration inﬁltration (Figure (Figure (Figure 3). For3). 3 For).this For thisreason, this reason, reason,they theyare theyhelpful are arehelpful in helpful the in the in initialtheinitial initial diagnosisdiagnosis diagnosis ofof aa of massmass a mass asas well aswell well as as determining as determining determining surgical surgical surgical resectability resectability resectability and andplanning and planning planning surgical surgical interventionsinterventions [25]. [25]. AA A specialspecial special CT CT CT protocol protocol protocol with with with delayed delayed (20 (20 min) min) images images is particularly is particularly valuable valuable in in suspectedsuspected casescases of ofof cholangiocarcinoma cholangiocarcinomacholangiocarcinoma (Figures (Figures (Figures4 and 4 and54). and In 5). summary, 5).In summary,In summary, non-invasive non-invasive non-invasive imaging imaging modalities imaging modalitiesaremodalities useful toare determine useful to to determine determine presence presence and presence location and and loca of loca stricture,tiontion of stricture, of butstricture, invasive but invasivebut imaging invasive imaging is imaging needed is needed is to needed obtain to obtain a diagnosis. toa diagnosis. obtain a diagnosis.

Figure 3. (A): Axial contrast-enhanced CT shows enhancing dilated common duct (arrow); (B): there is abrupt cutoff of the common duct and there is diffuse mural thickening and enhancement (arrow); (C): The circle demonstrates an infiltrative mass in the distal duct found on coronal CT; (D): endoscopic retrograde cholangiopancreatography (ERCP) shows a short-segment tight stricture corresponding to the mass. Biopsy confirmed cholangiocarcinoma. Diagnostics 2020, 10, x FOR PEER REVIEW 5 of 14 Diagnostics 2020, 10, x FOR PEER REVIEW 5 of 14

Figure 3. A: Axial contrast-enhanced CT shows enhancing dilated common duct (arrow); B: there is Figure 3. A: Axial contrast-enhanced CT shows enhancing dilated common duct (arrow); B: there is abrupt cutoff of the common duct and there is diffuse mural thickening and enhancement (arrow); C: abrupt cutoff of the common duct and there is diffuse mural thickening and enhancement (arrow); C: The circle demonstrates an infiltrative mass in the distal duct found on coronal CT; D: endoscopic The circle demonstrates an infiltrative mass in the distal duct found on coronal CT; D: endoscopic retrograde cholangiopancreatography (ERCP) shows a short-segment tight stricture corresponding retrograde cholangiopancreatography (ERCP) shows a short-segment tight stricture corresponding Diagnosticsto the2020 mass., 10, Biopsy 337 confirmed cholangiocarcinoma. 5 of 15 to the mass. Biopsy confirmed cholangiocarcinoma.

Figure 4. A: Axial arterial phase CT shows dilated intrahepatic ducts and a hypodense mass (arrow) Figure 4. A(A: ):Axial Axial arterial arterial phase phase CT CT shows shows dilated dilated intr intrahepaticahepatic ducts ducts and and a a hypodense hypodense mass mass (arrow) (arrow) at the hilum; B,C: venous phase images show enhancement of the mass. This signifies excessive at thethe hilum;hilum; (B,CB,C:): venous venous phase phase images images show show enhancement enhancement of the mass. This signiﬁessignifies excessive fibrous stroma in the tumor and is consistent with cholangiocarcinoma. ﬁbrousfibrous stroma in thethe tumortumor andand isis consistentconsistent withwith cholangiocarcinoma.cholangiocarcinoma.

Figure 5. A–C: CT shows a pancreatic head mass with central necrosis (circle, C). Additional findings Figure 5. 5. A(–AC–: CCT): CTshows shows a pancreatic a pancreatic head headmass with mass central with central necrosis necrosis (circle, C). (circle, Additional C). Additional findings include no calcifications to support underlying chronic pancreatitis, no ductal dilatation, ﬁndingsinclude includeno calcifications no calciﬁcations to support to support underlying underlying chronic chronic pancreatitis, pancreatitis, no no ductal ductal dilatation, peripancreatic fat planes are not maintained (blue arrow, A) and superior mesenteric artery (SMA) peripancreatic fat planes are not maintained (blue arrow, A) and superior mesenteric artery (SMA) (red(red arrow,arrow, A) A)/superior/superior mesenteric mesenteric vein vein (SMV) (SMV) (yellow (yellow arrow, arrow, A) ratio A) ratio is 1. is The ≥ 1. gastroduodenal The gastroduodenal artery (red arrow, A)/superior mesenteric vein (SMV) (yellow arrow, A) ratio≥ is ≥ 1. The gastroduodenal (greenartery (green arrow, B)arrow, is encased B) is encased by the mass.by the Dilated mass. D commonilated common bile duct bile (star, duct C). (star, Overall, C). Overall, there are there at least are artery (green arrow, B) is encased by the mass. Dilated common bile duct (star, C). Overall, there are threeat least signs three suggesting signs suggesting the diagnosis the diagnosis of malignancy. of malignancy. at least three signs suggesting the diagnosis of malignancy.

6. Invasive Imaging Methods 6. Invasive Imaging Methods InvasiveInvasive imagingimaging methodsmethods areare requiredrequired toto obtainobtain tissue samples from biliary strictures andand make Invasive imaging methods are required to obtain tissue samples from biliary strictures and make a definitivedefinitive diagnosis.diagnosis. Invasive Invasive methods methods are are also also able able to to directly visualize biliary obstruction; a definitive diagnosis. Invasive methods are also able to directly visualize biliary obstruction; however, these these modalities modalities are are more more likely likely to tohave have complications complications than than non-invasive non-invasive methods. methods. The however, these modalities are more likely to have complications than non-invasive methods. The Thefield fieldof invasive of invasive imaging imaging is israpidly rapidly expanding expanding past past the the more more traditional traditional ERCP, ERCP, endoscopicendoscopic field of invasive imaging is rapidly expanding past the more traditional ERCP, endoscopic ultrasound–fine-needleultrasound–fine-needle aspiration aspiration (EUS–FNA), (EUS–FNA), and and percutaneous percutaneous transhepatic transhepatic cholangiography cholangiography (PTHC) ultrasound–fine-needle aspiration (EUS–FNA), and percutaneous transhepatic cholangiography to(PTHC) include to cholangioscopy,include cholangioscopy, intraductal intraductal ultrasound, ultrasound, and confocal and laserconfocal endomicroscopy. laser endomicroscopy. (PTHC) to include cholangioscopy, intraductal ultrasound, and confocal laser endomicroscopy. 6.1. Endoscopic Retrograde Cholangiopancreatography 6.1. Endoscopic Retrograde Cholangiopancreatography 6.1. Endoscopic Retrograde Cholangiopancreatography ERCP-guided tissue acquisition is a useful modality in patients presenting with obstructive ERCP-guided tissue acquisition is a useful modality in patients presenting with obstructive jaundiceERCP-guided secondary tissue to biliary acquisition stricture is requiringa useful moda drainage.lity in Thepatients procedure presenting involves with passage obstructive of a jaundice secondary to biliary stricture requiring drainage. The procedure involves passage of a duodenoscopejaundice secondary through to thebiliary mouth stricture and into requiring the duodenum. drainage. From The the procedure duodenum, involves a catheter passage is threaded of a duodenoscope through the mouth and into the duodenum. From the duodenum, a catheter is throughduodenoscope the ampulla through into the the mouth common and bile into duct the over duodenum. a guidewire. From Following the duodenum, cannulation a catheter of the bile is threaded through the ampulla into the common bile duct over a guidewire. Following cannulation duct,threaded contrast through is injected the ampulla through into the the cannula common for bile fluoroscopic duct over imaging a guidewire. and better Following delineation cannulation of the of the bile duct, contrast is injected through the cannula for fluoroscopic imaging and better biliaryof the tree.bile duct, Because contrast of its abilityis injected to obtain through tissue the and cannula alleviate for obstruction, fluoroscopic ERCP imaging is the and preferred better delineation of the biliary tree. Because of its ability to obtain tissue and alleviate obstruction, ERCP is methoddelineation for patientsof the biliary with obstructivetree. Because jaundice of its ability and systemic to obtain symptoms tissue and in alleviate whom aobstruction, diagnosis cannot ERCP beis achieved with EUS–FNA alone [26].

There are two methods of obtaining tissue during ERCP: brushings of the biliary stricture for cytologic evaluation and forceps for intraductal biopsies under ﬂuoroscopic guidance. While ERCP has high speciﬁcity (95%) for diagnosing malignancy within biliary strictures, its sensitivity is low. Diagnostics 2020, 10, x FOR PEER REVIEW 6 of 14

the preferred method for patients with obstructive jaundice and systemic symptoms in whom a diagnosis cannot be achieved with EUS–FNA alone [26]. There are two methods of obtaining tissue during ERCP: brushings of the biliary stricture for Diagnostics 2020, 10, 337 6 of 15 cytologic evaluation and forceps for intraductal biopsies under fluoroscopic guidance. While ERCP has high specificity (95%) for diagnosing malignancy within biliary strictures, its sensitivity is low. BiliaryBiliary brushingsbrushings havehave aa sensitivitysensitivity ofof 23%–56%,23%–56%, biopsiesbiopsies havehave aa sensitivitysensitivity ofof 33%–65%,33%–65%, andand thethe combinationcombination of the two has a a sensitivity sensitivity of of 60%–70% 60%–70% [23]. [23]. Roth Roth et et al. al. demonstrated demonstrated that that cytology cytology of ofboth both the the brushings brushings and and biliary biliary fluid, fluid, aspirated aspirated fr fromom the the biliary biliary tree tree before before and after brushings, increasedincreased sensitivitysensitivity toto 84%.84%. AA newernewer methodmethod ofof obtainingobtaining tissuetissue throughthrough ERCPERCP isis scraping.scraping. RatherRather thanthan usingusing aa brushbrush toto obtain a sample from the stricture, the TrefleTrefle BiliaryBiliary ScraperScraper usesuses aa loopedlooped metalmetal wirewire toto shaveshave cellscells fromfrom aa biliarybiliary stricturestricture [27[27].]. NakaharaNakahara etet al.al. showedshowed thatthat thethe sensitivitysensitivity ofof thisthis methodmethod forfor diagnosingdiagnosing malignancymalignancy waswas 41%,41%, whichwhich waswas significantlysignificantly moremore sensitivesensitive thanthan traditionaltraditional cytologycytology [[28].28]. However, eveneven thethe scraper’sscraper’s sensitivity is low, andand manymany malignanciesmalignancies willwill bebe missedmissed usingusing thesethese ERCPERCP techniques.techniques. (Figure(Figure6 6))

FigureFigure 6.6. ERCP withwith brushingsbrushings andand resultantresultant cytology. cytology. ( AA):: Cholangiography Cholangiography showing distal bilebile ductduct stricturestricture withwith upstream upstream ductal ductal dilatation. dilatation. (B B):: Balloon dilationdilation of of distal distal bile bile duct duct stricture. stricture. (C C):: Brushings obtainedobtained fromfrom distal distal bile bile duct duct stricture stricture during during ERCP. ERCP. (D): Plastic D: Plastic stent placedstent placed in bile ductin bile across duct stricture across forstricture biliary for drainage. biliary (drainage.E): Brush E cytology: Brush showedcytology biliary showed tract biliary adenocarcinoma. tract adenocarcinoma. The group showsThe group loss ofshows polarity, loss irregularlyof polarity, spaced irregularly nuclei. spaced The nucleinuclei. are The angulated nuclei are and angulated pointed withand pointed subtle grooves with subtle and folding.grooves Smalland folding. nucleoli Small are present nucleoli in are the pr cellsesent (Papanicolaou in the cells (Papanicolaou stain). stain).

MoreMore advancedadvanced cytologicalcytological techniquestechniques have beenbeen developeddeveloped toto improveimprove sensitivitysensitivity ofof brushbrush cytology.cytology. Obtaining cells from the brushes once they are removedremoved fromfrom thethe bodybody involvesinvolves eithereither smearingsmearing thethe brushbrush directlydirectly ontoonto aa glassglass slideslide oror placingplacing thethe brushbrush inin aa preservativepreservative fluidfluid andand thenthen centrifugingcentrifuging thisthis liquidliquid toto isolateisolate thethe cells.cells. Either way, thethe samplessamples areare fixedfixed andand stainedstained withwith variousvarious stains,stains, includingincluding PapanicolaouPapanicolaou andand May-GrünwaldMay-Grünwald Giemsa.Giemsa. PathologistsPathologists cancan thenthen identify pathologic oror malignantmalignant cellcell featuresfeatures throughthrough microscopicmicroscopic evaluationevaluation [[25].25]. ResearchersResearchers havehave recentlyrecently expandedexpanded uponupon conventionalconventional brushbrush cytologycytology to identify otherother markers of malignancy withinwithin the brushed cells, includingincluding microRNAmicroRNA (miRNA),(miRNA), transfertransfer RNARNA (tRNA),(tRNA), andand DNADNA mutations.mutations. miRNAmiRNA hashas provedproved anan importantimportant biomarkerbiomarker forfor diagnosisdiagnosis ofof biliarybiliary malignancies.malignancies. ThisThis moleculemolecule alsoalso enhancesenhances sensitivitysensitivity ofof brushbrush cytology.cytology. Le Le et et al. al. showed showed that that the the sensitivity sensitivity of brush of brush cytology cytology increased increased from from 54% to54% 85% to when 85% addingwhen adding miRNA miRNA staining staining [29]. Jang [29]. et Jang al. recently et al. recently studied studied staining staining biliary biliary samples samples for methionyl-tRNA for methionyl- synthetase 1 (MARS1). tRNA molecules are integral to protein catalysis within cells and they also play a role in cancer development. Immunohistochemical and immunofluorescent staining for MARS1 had a sensitivity of 70% and specificity of 96% for diagnosing malignancy for 80 patients with biliary Diagnostics 2020, 10, x FOR PEER REVIEW 7 of 14

tRNA synthetase 1 (MARS1). tRNA molecules are integral to protein catalysis within cells and they

Diagnosticsalso play2020 a role, 10, in 337 cancer development. Immunohistochemical and immunofluorescent staining7 of for 15 MARS1 had a sensitivity of 70% and specificity of 96% for diagnosing malignancy for 80 patients with biliary strictures [30]. Fluorescence in situ hybridization (FISH) has also been studied on brush stricturescytology specimens. [30]. Fluorescence Because inFISH situ testing hybridization identifies (FISH) chromosomal has also beenabnormalities studied on in brush80% of cytology biliary specimens.cancers, researchers Because FISHhypothesized testing identifiesthat FISH chromosomal would improve abnormalities identification in 80% of ofmalignant biliary cancers, biliary researchersstrictures from hypothesized ERCP sampling. that FISH Indeed, would FISH improve in combination identification with of malignant brush cytology biliary stricturesdid modestly from ERCPimprove sampling. sensitivity Indeed, to 50%–60% FISH in [31]. combination with brush cytology did modestly improve sensitivity to 50%–60%Despite [31these]. new cytological markers, one barrier to high sensitivity with cytology is insufficientDespite cellular these new sampling. cytological Brush markers, cytology one may barrier return to high inadequate sensitivity cellularity with cytology due to is factors insufficient like cellulartissue fibrosis, sampling. tissue Brush ulceration, cytology and may patterns return inadequateof invasion cellularitysuch as submucosal due to factors spread like [32]. tissue Mutation fibrosis, tissueprofiling ulceration, (MP) is andadvantageous patterns of because invasion it such samples as submucosal free DNA spreadrather than [32]. intact Mutation cells. profiling The free (MP) DNA is advantageouscan be found in because the preservative it samples freefluid DNA holding rather the than biliary intact brush cells. after The it free is centrifuged DNA can be and found cells in theare preservativeremoved. The fluid DNA holding can then the biliarybe evaluated brush after for itse isveral centrifuged mutations and known cells are to removed.be associated The DNAwith canmalignancy. then be evaluated Kushnir et for al. several reported mutations that brush known cytology to be plus associated MP had with a sensitivity malignancy. of 56%, Kushnir which et al.is reportedsignificantly that more brush sensitive cytology than plus brush MP had cytology a sensitivity alone. This of 56%, article which found is significantly that the highest more sensitivity sensitive than(66%–69%) brush cytologywas achieved alone. by This using article brush found cytology, that the FISH, highest and sensitivityMP together. (66%–69%) There was was no achieved difference by usingin specificity brush cytology, amongst FISH, these and three MP tests. together. Perhaps There the was greatest no diff erencebenefit inof specificity MP was amongstincreasing these the threediagnostic tests. yield Perhaps on brush the greatest samples benefit from of22% MP for was tradit increasingional cytology the diagnostic to 100% yield [27]. onAs brushthe analysis samples of fromERCP 22% samples for traditional continue cytology to be tostudied 100% [and27]. Asexpanded, the analysis ERCP of ERCP will samplesbecome continueeven more to be adept studied at anddiagnosing expanded, malignant ERCP willbiliary become strictures even [31]. more adept at diagnosing malignant biliary strictures [31].

6.2. Cholangioscopy Per Oral Cholangioscopy (POCS) involves passagepassage of a choledochoscopecholedochoscope through the working channel ofof a duodenoscopea duodenoscope into into the biliary the biliary tract. Thistract. provides This provides direct, not direct, just fluoroscopic, not just fluoroscopic, visualization ofvisualization the biliary tractof the [4 ].biliary The recent tract introduction[4]. The recent of a singleintroduction operator of digital a single cholangioscope operator digital called Spyglasscholangioscope DS (Boston called Scientific Spyglass Corp) DS (Boston has allowed Scientific POCS Corp) to become has allowed one of the POCS primary to become tools in one diagnosis of the ofprimary MBS [ 33tools]. in diagnosis of MBS [33]. POCS allows for evaluation of the stricture based on its appearanceappearance as aberrant mucosal and vascular patternspatterns areare suspicioussuspicious for for malignancy. malignancy. The The visual visual findings findings of of POCS POCS alone alone have have a sensitivitya sensitivity of 88.9%of 88.9% and and specificity specificity of 97.6% of 97.6% for predicting for predicting malignancy malignancy [34]. POCS [34]. alsoPOCS permits also permits targeted targeted tissue biopsies tissue withbiopsies a sensitivity with a sensitivity of 71%–100% of 71%–100% and a specificity and a specificity of 96.7%–100% of 96.7%–100% [33]. Additionally, [33]. Additionally, POCS-directed POCS- biopsiesdirected havebiopsies shown have greater shown diagnostic greater diagnostic ability than ability brushings than andbrushings fluoroscopic-guided and fluoroscopic-guided biopsies of biliarybiopsies strictures of biliary obtained strictures during obtained ERCP during [35] (Figure ERCP 7[35]). (Figure 7).

Figure 7. (A): Cholangioscopy revealing hilar stricture with irregular mucosa and neovascularization. (B): Stricture sampling with SpyBite biopsy forceps. Diagnostics 2020, 10, x FOR PEER REVIEW 8 of 14

Figure 7. A: Cholangioscopy revealing hilar stricture with irregular mucosa and neovascularization. B: Stricture sampling with SpyBite biopsy forceps.

One of the barriers to widespread use of POCS is limited interobserver agreement (IOA). Sethi et al. reported an IOA of 45% [36]. This led Sethi et al. to develop the Monaco classification system to streamline IOA. They identified eight criteria including presence of stricture, presence of lesion, mucosal features, papillary projections, ulceration, abnormal vessels, scarring, and pronounced pit pattern. The adoption of this classification system increased IOA to 70% [37]. POCS should be utilized after EUS–FNA/FNB and standard ERCP techniques have failed to provide a diagnosis due to high cost and increased risk of adverse events with POCS [38]. In a large retrospective review of almost 4000 procedures, POCS showed an increased adverse event rate of 7% versus 2.9% with traditional ERCP [39]. Cholangioscopy is a promising technology; however, additional research is needed to standardize findings, increase IOA, and to reduce the complication Diagnosticsrate [37]. 2020, 10, 337 8 of 15

6.3. EndoscopicOne of the Ultrasound-Guided barriers to widespread Fine-Needle use of POCS Aspiration is limited interobserver agreement (IOA). Sethi et al. reportedBiliary an strictures IOA of 45% associated [36]. This with led a mass Sethi lesion et al. found to develop on cross-sectional the Monaco classificationabdominal imaging system are to streamlineoften further IOA. imaged They and identified sampled eight with criteriaendoscop includingic ultrasound-guided presence of stricture,fine-needle presence aspiration of lesion,(EUS– mucosalFNA). These features, mass papillary lesions projections, include ulceration,primary abnormalHPB malignancy, vessels, scarring, metastatic and pronouncedtumors, and pit pattern.lymphoproliferative The adoption disorders. of this classification During this system procedure, increased an echoendoscope IOA to 70% [37 is]. advanced into the upper gastrointestinalPOCS should tract, be where utilized adja aftercent EUS–FNA organs can/FNB be visualized and standard with ERCP greater techniques detail in comparison have failed to providenon-invasive a diagnosis imaging. due A to FNA high needle cost and is advanc increaseded through risk of adverse the working events channel with POCS and directed [38]. In aunder large retrospectivereal-time sonographic review of imaging almost 4000 toward procedures, the target POCS lesion showed (Figure an 8). increased adverse event rate of 7% versusA 2.9%fine-needle with traditional aspirate ERCPis obtained [39]. Cholangioscopyand cytological isanalysis a promising is performed technology; from however, this aspirate. additional This researchprocedure is has needed a sensitivity to standardize of 80% findings,and a specificity increase of IOA, 97% andto identify to reduce malignancy the complication [31,40]. The rate benefits [37]. of EUS–FNA include not only high sensitivity, but also widespread availability, low cost, and the 6.3. Endoscopic Ultrasound-Guided Fine-Needle Aspiration ability to evaluate lesions not seen on imaging [41]. EUS–FNA is favored over ERCP in asymptomatic patientsBiliary who stricturesdo not require associated biliary withdrainage a mass[26]. Of lesion note, foundEUS–FNA on is cross-sectional typically avoided abdominal in hilar imagingcholangiocarcinoma are often further due to imagedconcern and for tumor sampled seedin withg endoscopic[42]. This concern ultrasound-guided is the greatest fine-needle barrier to aspirationwidespread (EUS–FNA). use of EUS–FNA. These Yamaguchi mass lesions et al. include report primaryed a case HPB of a solid malignancy, pseudopapillary metastatic neoplasm tumors, andof the lymphoproliferative pancreas that was seeded disorders. into During the gastric this wa procedure,ll 5 years an after echoendoscope the original EUS–FNA is advanced procedure into the upper[43]. Ultimately gastrointestinal however, tract, only where three adjacent such organs cases canhave be been visualized reported with in greater the literature. detail in comparison Therefore, toconcern non-invasive for malignant imaging. peritoneal A FNA needleseeding is should advanced not throughpreclude the utilization working and channel further and investigation directed under of real-timethis effective sonographic diagnostic imaging tool [44]. toward the target lesion (Figure8).

Figure 8.8. (A:A): Endoscopic Endoscopic ultrasound ultrasound (EUS)-guided (EUS)-guided fine-nee ﬁne-needledle aspiration aspiration of of a a pancreatic pancreatic head head mass. (BB:): The The malignant malignant cells cells are are crowded crowded and and overlapping. overlapping. The The nuclei nuclei are are enlarged enlarged and show nuclear size variation in a range ofof 1:3.1:3. (FNA, Papanicolaou stain).

6.4. EndoscopicA fine-needle Ultrasound-Guided aspirate is obtained Fine-Needle and Biopsy cytological analysis is performed from this aspirate. This procedure has a sensitivity of 80% and a specificity of 97% to identify malignancy [31,40]. The benefitsEndoscopic of EUS–FNA ultrasound-guided include not fine-needle only high sensitivity,biopsy (EUS-FNB) but also is widespread similar to EUS–FNA, availability, but low it uses cost, anda larger the bore ability needle to evaluate capable lesionsof obtaining not seen core on biop imagingsies from [41 the]. EUS–FNAsuspect lesion is favored (Figure over9). Numerous ERCP in asymptomatic patients who do not require biliary drainage [26]. Of note, EUS–FNA is typically avoided in hilar cholangiocarcinoma due to concern for tumor seeding [42]. This concern is the greatest barrier to widespread use of EUS–FNA. Yamaguchi et al. reported a case of a solid pseudopapillary neoplasm of the pancreas that was seeded into the gastric wall 5 years after the original EUS–FNA procedure [43]. Ultimately however, only three such cases have been reported in the literature. Therefore, concern for malignant peritoneal seeding should not preclude utilization and further investigation of this effective diagnostic tool [44]. Diagnostics 2020, 10, 337 9 of 15

6.4. Endoscopic Ultrasound-Guided Fine-Needle Biopsy DiagnosticsEndoscopic 2020, 10, x ultrasound-guided FOR PEER REVIEW fine-needle biopsy (EUS-FNB) is similar to EUS–FNA, but it9 uses of 14 a larger bore needle capable of obtaining core biopsies from the suspect lesion (Figure9). Numerous studies have compared the efficacy of EUS-FNB to EUS–FNA. Van Riet et al. performed a randomized studies have compared the efficacy of EUS-FNB to EUS–FNA. Van Riet et al. performed a randomized study of over 600 patients with biliary strictures. The FNB needle provided higher histologic yield study of over 600 patients with biliary strictures. The FNB needle provided higher histologic yield (77% vs. 44%) and increased diagnostic accuracy (87% vs. 78%) compared to FNA [45,46]. EUS-FNB (77% vs. 44%) and increased diagnostic accuracy (87% vs. 78%) compared to FNA [45,46]. EUS-FNB has also been shown to provide more core tissue and nucleic acid yield than FNA samples [47]. More has also been shown to provide more core tissue and nucleic acid yield than FNA samples [47]. studies are needed to demonstrate diagnostic superiority of FNB over FNA, especially when using More studies are needed to demonstrate diagnostic superiority of FNB over FNA, especially when rapid on-site evaluation (ROSE) [48]. ROSE involves immediate evaluation of the sample at the time using rapid on-site evaluation (ROSE) [48]. ROSE involves immediate evaluation of the sample at the of biopsy, thus determining whether the tissue is adequate for diagnosis. The diagnostic yield of time of biopsy, thus determining whether the tissue is adequate for diagnosis. The diagnostic yield EUS–FNA with ROSE was not significantly different than EUS-FNB without ROSE [49]. Overall, EUS- of EUS–FNA with ROSE was not significantly different than EUS-FNB without ROSE [49]. Overall, FNB provides a reliable alternative to EUS–FNA with increased diagnostic accuracy, especially when EUS-FNB provides a reliable alternative to EUS–FNA with increased diagnostic accuracy, especially ROSE is not available. when ROSE is not available.

Figure 9. A Figure 9. A( : ):Malignant Malignant glands glands admixed admixed with with normal normal panc pancreaticreatic parenchyma parenchyma (core (core biopsy, biopsy, H&E H&E stain). stain). (B): On high power, the tumor cells form solid nest with focal glandular formation. There is nuclear B: On high power, the tumor cells form solid nest with focal glandular formation. There is nuclear enlargement and irregularity, abnormal chromatin, and prominent nucleoli (core biopsy, H&E stain). enlargement and irregularity, abnormal chromatin, and prominent nucleoli (core biopsy, H&E stain). Classically, only biopsies obtained during surgical procedures provided sufficient samples of the Classically, only biopsies obtained during surgical procedures provided sufficient samples of tissue in question. However, endoscopic samples are now adequate for genomic analysis and next the tissue in question. However, endoscopic samples are now adequate for genomic analysis and next generation sequencing (NGS) thanks to these improved techniques in endoscopic ultrasound tissue generation sequencing (NGS) thanks to these improved techniques in endoscopic ultrasound tissue acquisition. Valero et al. assessed the variability between endoscopic biopsy and surgical biopsy acquisition. Valero et al. assessed the variability between endoscopic biopsy and surgical biopsy with with NGS and reported 100% endoscopic sample agreement with genomic sampling of surgically NGS and reported 100% endoscopic sample agreement with genomic sampling of surgically acquired acquired specimens [50]. EUS-FNB microcore samples have better tissue integrity and microscopic specimens [50]. EUS-FNB microcore samples have better tissue integrity and microscopic tissue tissue architecture over EUS–FNA, allowing for the use of innovative biomarker evaluation [51]. architecture over EUS–FNA, allowing for the use of innovative biomarker evaluation [51]. 6.5. Intraductal Ultrasound 6.5. Intraductal Ultrasound Intraductal ultrasound (IDUS) is a technique used during ERCP, in which an ultrasound probe is advancedIntraductal through ultrasound the working (IDUS) channel is a technique of the duodenoscope used during into ERCP, the biliaryin which system. an ultrasound IDUS provides probe real-timeis advanced imaging through of the the stricture working using channel high frequencyof the duodenoscope ultrasound andinto helps the biliary to identify system. malignant IDUS characteristicsprovides real-time including imaging hyperechoic, of the stricture asymmetric using high wall frequency thickening, ultrasound irregular and borders, helps and to identify abrupt shoulders.malignant characteristics Studies have shown including a sensitivity hyperechoic, and specificity asymmetric of wall 98% forthickening, diagnosis irregular of MBS. borders, While IDUS and hasabrupt an impressiveshoulders. Studies sensitivity have based shown on a sensitivity sonographic and appearance specificity of 98% stricture for diagnosis alone, this of MBS. technology While canIDUS also has be usedan impressive for ultrasound-guided sensitivity based biopsies. on Insonographic fact, IDUS-guided appearance biopsy of hasstricture demonstrated alone, this an improvedtechnology sensitivity can also over be fluoroscopicused for ultrasound-gui biopsy (87% vs.ded 67%). biopsies. This technologyIn fact, IDUS-guided is promising, biopsy but its rolehas withindemonstrated the diagnostic an improved algorithm sensitivity of biliary over strictures fluorosc isopic still beingbiopsy refined (87% [vs.4,52 67%).–54]. This technology is promising, but its role within the diagnostic algorithm of biliary strictures is still being refined [4,52– 54].

Diagnostics 2020, 10, 337 10 of 15

6.6. Confocal Laser Endomicroscopy Confocal laser endomicroscopy (CLE) is a novel endoscopic technology used to obtain real-time histopathologic diagnosis of biliary strictures. During this procedure, confocal miniprobes are passed through the ERCP catheter and fluorescein dye is administered to produce high-resolution images of the biliary stricture at a microscopic level. CLE probes visualize biliary epithelium by transmitting low-power laser and detecting light reflected back from the tissue. Almadi et al. studied CLE effectiveness in evaluating biliary strictures in comparison to ERCP. They noted an increased sensitivity with a combination of CLE and ERCP (98%) in comparison to ERCP alone (45%) [55,56]. However, specificity and the positive predictive value were decreased with the combination. As a result, they concluded that CLE should be reserved for strictures that are still indeterminate after intraductal ultrasound and cholangioscopy [57]. CLE requires additional training and does not provide a significant advantage over other technologies. Provider variability is considered CLE’s greatest obstacle to widespread use. The Miami classification was developed to streamline and advance its accuracy over other technologies. This classification system describes four criteria that are considered highly suspicious for malignancy. These include thick white bands, thick dark bands, dark clumps, and epithelial structures. The presence of one feature renders a 97% sensitivity and 33% specificity for identifying malignancy [58,59]. Due to Miami’s low specificity, the Paris classification was developed to describe benign biliary strictures. Benign strictures are characterized by thickened reticular strictures, multiple thin white bands, increased spaces between scales, and dark granular patterns with scales. Additional studies are needed to determine whether combining Miami and Paris classifications will improve diagnostic utility of CLE. Until further research is conducted, CLE should remain reserved for indeterminate strictures after other advanced invasive diagnostic techniques are utilized [4]. Sensitivity and specificity of various MBS diagnostic modalities can be found in Table1.

6.7. Percutaneous Transhepatic Cholangiography PTHC is a radiologic procedure that directly accesses the biliary system through ultrasound-guided percutaneous needle placement into the bile duct. This allows for fluoroscopic imaging of the biliary tree with injected contrast, biopsies of biliary tissue, drainage of fluid upstream of the obstruction, and cytology on the drained fluid to aid in diagnosing stricture etiology [60]. PTHC is reserved for patients when diagnosis is not achieved with invasive imaging or when patients are too unstable to undergo endoscopic procedures [61]. This procedure is only used for such select cases because it has a complication rate ranging from 0.5% to 2.5% [62]. Overall, endoscopic procedures are quickly evolving to increase diagnostic power for diagnosing malignant biliary strictures. These procedures require additional training for providers, and are associated with high risk for complications, particularly cholangitis [63]. However, as these techniques are refined and further studied, they will likely streamline the diagnosis of malignant biliary strictures, with fewer procedures required to make a definitive diagnosis. Diagnostics 2020, 10, 337 11 of 15

Table 1. Sensitivity and speciﬁcity of various MBS diagnostic modalities.

Diagnostics of Malignant Biliary Strictures Modality Sensitivity (%) Specificity (%) Reference Lab markers CA 19-9 80 89–90 Hasan et al. [10] CEA 30–68 75–95 Yue et al. [12] Non-invasive imaging MRCP 38–90 70–85 Singh et al. [23] CT 75–80 60–80 Singh et al. [23] US 90–95 30–70 Kapoor et al. [6] Invasive Imaging PTHC 71 48 Kim et al. [62] ERCP Brushing cytology 23–56 95 Singh et al. [23] Fluoroscopic biopsy 33–65 95 Singh et al. [23] Brushing + fluoroscopic biopsy 60–70 95 Singh et al. [23] Brushing + bile fluid 84 95 Roth et al. [27] Brushing + miRNA 54–85 95 Le et al. [29] Brushing + FISH 50–60 95 Kushnir et al. [31] Brushing + MP 56 95 Kushnir et al. [31] Brushing + FISH + MP 66–69 95 Kushnir et al. [31] EUS–FNA 80 97 Nakai et al. [26] Cholangioscopy 88.9 97.6 Kulpatcharapong et al. [34] Cholangioscopy directed biopsy 71–100 96.7–100 Ayoub et al. [33]

7. Conclusions Prompt diagnosis of MBS with biomarkers, contrast-enhanced CT, MRCP with contrast-enhanced MRI, and advanced endoscopic techniques are crucial to provide the greatest survival beneﬁt for patients. ERCP with brushing, scraping, and intraductal biopsies is the preferred method of invasive imaging for biliary strictures requiring biliary drainage. EUS–FNA is favored when non-invasive imaging demonstrates a mass lesion associated with a stricture or when ERCP is unsuccessful in revealing a diagnosis. Cholangioscopy provides direct visualization of the biliary stricture and permits targeted tissue biopsy. Tissue samples taken from these procedures are undergoing experimental evaluation and processing to enhance diagnostic yield. The advances in tissue sampling and diagnosis may lead into a new era of personalized medicine by allowing for targeted gene therapy for MBS in the future. The role of confocal laser endomicroscopy continues to evolve given the high cost and provider variability associated with this technique. The recent advances described in this review have allowed for more comprehensive evaluation, understanding, and eﬀective diagnosis of the disease process.

Funding: This research received no external funding. Conﬂicts of Interest: The authors declare no conﬂict of interest.

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