Predicting cannulation difficulty in endoscopic retrograde cholangiopancreatography using CT image findings: a decision-tree analysis

Abstract

Background

Difficult cannulation during endoscopic retrograde cholangiopancreatography (ERCP) is associated with increased complications; therefore, its prediction is important.

Purpose

To identify radiologic risk factors of difficult cannulation during ERCP based on computed tomography (CT) findings and to develop a predictive model for a difficult cannulation.

Material and Methods

A total of 171 patients with native papilla who underwent both enhanced CT and ERCP were recruited. Two radiologists independently measured the distal common bile duct (CBD) diameter and choledochoduodenal (CD) angle and analyzed CT images for presence of CBD stone and papilla bulging, size and type of periampullary diverticulum (PAD), and duodenal segment in which major papilla was located. Multivariate logistic regression analysis and decision-tree analysis were performed to identify risk factors for difficult cannulation.

Results

Thirty-nine patients underwent a difficult cannulation. The multivariate logistic regression analysis revealed that a smaller CBD diameter, presence of papilla bulging, location of the major papilla other than the descending duodenum, a smaller CD angle, and a higher worrisome PAD score were statistically relevant factors for difficult cannulation (P < 0.049). In the decision-tree analysis, a higher worrisome PAD score was the strongest predictor of difficult cannulation, followed by the presence of papilla bulging, smaller CD angle, and a smaller CBD diameter. The predictive model had an 82.5% overall predictive accuracy.

Conclusion

The CT findings-based decision-tree analysis model showed a high accuracy in predicting cannulation difficulty and may be helpful for making pre-ERCP strategy.

Keywords

Endoscopic retrograde cholangiopancreatography multidetector computed tomography decision-tree analysis post-ERCP pancreatitis precision medicine image reconstruction

Introduction

Endoscopic retrograde cholangiopancreatography (ERCP) is frequently performed in patients with hepatobiliary and pancreatic diseases for both diagnostic and therapeutic purposes (1). The ERCP procedure involves passage of an endoscope into the duodenum, proper scope placement below the papilla, adequate visualization of the papilla, and cannulation of the common bile duct (CBD) using a sphincterotome (2,3). Successful selective biliary cannulation is the first step for a successful ERCP procedure. According to the European Society of Gastrointestinal Endoscopy clinical guidelines, the cannulation is considered difficult when it takes > 5 min, when it is repeated > 5 times, or when more than one unintended pancreatic duct manipulation is done (1). A study reported that the successful deep cannulation rate can be as low as 43% when performed by beginners and that the consistent success rate should be > 80% after training sessions, suggesting that the cannulation may fail in up to 20% of cases, even in experienced hands (4). Repeated cannulation attempts and inadvertent manipulation of the pancreatic duct may cause mechanical and chemical injuries to the papilla and pancreatic duct and may lead to a higher rate of post-procedural complications (5). Therefore, a successful selective biliary cannulation with minimal attempts is essential to reduce patient morbidity and mortality.

Ultrasound, computed tomography (CT), and magnetic resonance cholangiopancreatography (MRCP) are performed for the non-invasive diagnosis of hepatobiliary and pancreatic diseases (6). The advantages of CT are lower cost, shorter scan time, and wider differential diagnostic considerations, which is useful in patients who present with unusual symptoms or signs (7). In addition, various anatomic structures can be analyzed accurately through a two- or three-dimensional (3D) reconstruction without increasing the radiation dose (8). For this reason, CT is widely performed before ERCP in clinical settings.

Successful cannulation depends not only on the experience of the endoscopist, but also on various anatomic factors and underlying conditions in the patients (1,3). Many researchers tried to investigate the relationship between such factors and cannulation difficulty (1,2,5,9–18). However, the results of these studies have little utility in preprocedural settings because these studies evaluated various factors obtained during ERCP. To the best of our knowledge, there are no studies conducted to identify the radiologic risk factors for difficult cannulation. Because many patients with hepatobiliary and pancreatic diseases undergo CT scan before ERCP, predicting the cannulation difficulty based on the CT findings would help to prepare the procedure and establish treatment plans. The role of the cross-sectional imaging can be diversified from the diagnosis to the prediction of procedural complexity before the ERCP.

Therefore, the aim of the present study was to identify risk factors of difficult cannulation during ERCP based on preprocedural abdominal CT findings and to develop a predictive model for a difficult cannulation.

Material and Methods

Study population

This retrospective study was approved by the institutional review board, and the requirement for informed consent was waived. We searched the electronic records database of Korea University Anam Hospital for patients who underwent ERCP from October 2017 to June 2018. Of the registered 512 patients, 192 consecutive patients who underwent contrast-enhanced CT at the same hospital within one month before the ERCP and had no history of previous sphincterotomy were included. The patients who had a periampullary mass (n = 16), a choledochal cyst (n = 1), and those with a history of a previous Billroth II surgery (n = 4) were excluded. Finally, 171 patients were enrolled in our study (92 men, 79 women; age range = 23–90 years; Fig. 1).

Fig. 1.

Flowchart of patient selection, inclusion, and exclusion.

Multidetector-row CT technique

All CT examinations were performed using one of the following four 64-multidetector-row helical CT scanners: Ingenuity Core 128 (128-channel; Philips Healthcare,Cleveland, OH, USA), IQon Spectral CT (128-channel; Philips Healthcare), SOMATOM Definition Flash (64-channel; Siemens Healthcare, Iselin, NJ, USA), and SOMATOM Definition AS+ (64-channel; Siemens Healthcare). Scanning parameters were as follows: tube voltage = 100–120 kVp; effective tube current = 103–300 mAs with dose modulation; field of view = 250 × 250 mm; matrix = 516 × 512 pixels; collimation = 64 × 0.625 mm; and reconstruction kernel algorithm = soft tissue. Slice thickness was 3 mm in both the axial and coronal reconstructed planes. All CT images were obtained using intravenous contrast material (Hexosure 300, LG Chem; Iomeron 300, Bracco; Pamiray 300, Dongkook Pharm; Xenetix 300, Guerbet) at a rate of 2.5–4 mL/s, followed by a 20-mL saline flushing using a power injector. The arterial phase contrast images were obtained with a delay of 30–45 s after the contrast injection and the portal venous phase images with a delay of 70 s.

Image analysis

Before the interpretation, a second-year resident (S.H.L.) reconstructed the 3D multiplanar image by adjusting the angle so that the distal CBD and adjacent duodenum could be seen in the same plane (Fig. 2). Aquarius Intuition Edition Ver. 4.4.12 (TeraRecon, Foster City, CA, USA), a commercially available 3D reconstruction software, was used to reconstruct the images. The images were then sent to a picture archiving and communication system (Infinitt PACS, version 3.0; Infinitt Healthcare, Seoul, Republic of Korea).

Fig. 2.

Three-dimensional multiplanar reconstruction image. (a, b) In original image, the distal CBD and descending duodenum are not in the same plane on the coronal image. (c, d) The images were rotated so that the distal CBD and descending duodenum could be seen in the same plane on the coronal image. CBD, common bile duct.

Using the reconstructed image, two board certified radiologists (K.C.S. and N.Y.H. with 7 years and 11 years of experience in abdominal imaging, respectively) independently measured the angle between the distal CBD and adjacent duodenum, which we defined as the choledochoduodenal (CD) angle. A detailed method of measuring the CD angle is given in Fig. 3. The reviewers also measured the maximal transverse diameter of the CBD within 2 cm from the major papilla on the reconstructed image. The diameter was measured from the outer wall to the outer wall of the CBD.

Fig. 3.

Method of measuring the choledochoduodenal angle. (a) A coronal reconstructed image showing the distal CBD and adjacent duodenum in the same plane. CBD is inserting into the descending duodenum. (b) Two lines were drawn; a centerline of the distal CBD (dashed line) and a centerline of the adjacent duodenum (solid line). (c) At the point of the bile duct termination, a tangent line was drawn (dotted line marked a). Where the tangent line met the centerline of the duodenum, another tangent line was drawn (dotted line marked b). Then, the angle between the two tangent lines was measured (alpha). CBD, common bile duct.

The two radiologists independently analyzed other radiologic features, including the type and size of periampullary diverticulum (PAD), presence of radiologically visible far distal CBD stones, presence of papilla bulging, and the duodenal segment in which the major papilla was located (Fig. 4). In case of a disagreement, they assessed the CT images again until a consensus was reached. The reviewers were blinded to the ERCP findings and clinical backgrounds of the patients, such as underlying diseases and indications for ERCP.

Fig. 4.

Reconstructed CT images of two different patients with a location of the major duodenal papilla other than the descending duodenum. (a) The distal end of the common bile duct (thick arrow) is located in the junction between the descending and horizontal duodenum. A tiny periampullary diverticulum is noted (thin arrow). (b) The distal end of the common bile duct (thick arrow) is located in the horizontal duodenum. A periampullary diverticulum is also noted (thin arrow).

Boix et al. (9) categorized PAD based on the positional relationship between the papilla and diverticulum and defined type I PAD when the papilla was located inside the diverticulum. Based on this, radiological type I PAD was defined when the distal end of the CBD was not visible as it inserted directly into the PAD, or when the PAD was encasing the distal end of the CBD >180° (Fig. 5). The size of the PAD was defined as the largest diameter measured in the axial or coronal planes. One point was given to a type I PAD and another point was given to a PAD >1.5 cm. These points were added up to calculate what we called a “worrisome PAD score.” The normal papilla can be barely distinguished from the surrounding duodenal mucosal folds and, if distinguishable, it is almost always < 1 cm in diameter (19,20). Therefore, we defined papilla bulging as a prominent protuberance of the papilla measuring >1 cm in diameter on the axial or coronal plane images.

Fig. 5.

Axial (a) and reconstructed (b) CT images ∼ CT images of a patient who was reported to have type I periampullary diverticulum. The periampullary diverticulum (thin arrows) was encasing the distal end of the common bile duct (thick arrow) > 180°.

Clinical information

ERCP was performed using a side-viewing duodenoscope (JF 240 or TJF-260V; Olympus Medical Systems Co. Ltd., Tokyo, Japan) under conscious-deep sedation. Selective biliary cannulation was performed by the conventional technique using an ERCP catheter taper (MTW Endoskopie, Wesel, Germany). All procedures were performed by three experienced endoscopists, each with > 5 years of experience. The cannulation time was calculated by subtracting the time when the catheter tip got inside the papilla and the time when the common bile duct was visualized. The cannulation time and the use of additional techniques were obtained from written records of the endoscopists. The additional techniques included wire-guided cannulation, double-guidewire technique, autotome technique, and precutting using needle knife. The cannulation was defined as difficult when it took >5 min, when it failed due to any cause, or when additional techniques were used. We analyzed the laboratory results performed within 24 h before the ERCP procedure. The age, gender, aspartate aminotransferase (AST), alanine aminotransferase (ALT), total bilirubin levels, and the final diagnosis of the periampullary pathology were obtained from the electronic medical records.

Statistical analysis

The Chi-square test, Fisher’s exact test, linear by linear regression test, Student’s t-test, and Mann–Whitney U test were used to compare the factors between the patients with and without cannulation difficulty, as appropriate. Eleven potentially relevant risk factors were assessed using multivariate logistic regression analysis. To assess the reliability of the measurements, intraclass correlation coefficients (ICCs) were used. ICC values of ≤0, 0–0.20, 0.21–0.40, 0.41–0.60, 0.61–0.80, and >0.81 indicated negative, positive but poor, fair, moderate, good, and excellent agreement, respectively.

To generate a prediction model that would identify patients with cannulation difficulty, a decision tree was obtained using the classification and regression tree algorithm including all radiologic and clinical findings as predictor variables. The algorithm uses a binary recursive process splitting subsets of the complete dataset repeatedly into two child nodes to select the best predictor and to calculate optimal cut-off points for the continuous variables (21,22). The minimum number of cases was set as 10 in the parent node and 5 in the child node. The maximum tree depth, which means the maximum number of levels, was automatically set to 5. A 10-fold cross-validation was performed to produce an optimal decision-tree model. We used the commercially available software SPSS, version 22.0 (IBM Corp., Armonk, NY, USA) to perform the statistical analysis. P values < 0.05 were considered statistically significant.

Results

Characteristics of the included patients

The demographic, radiologic, and clinical characteristics of the included patients are shown in Table 1. Among 171 cases, 39 (22.8%) cases were considered to have had cannulation difficulty: 37 cases in which the cannulation time was > 5 min and two cases in which the cannulation failed. Additional techniques were used in 25 patients and in all cases where additional techniques were used, the cannulation time was > 5 min.

Table 1.

Patient characteristics according to the cannulation difficulty.

	Cannulation difficulty		t-value (Z)*	P value^†
	– (n = 132)	+ (n = 39)	t-value (Z)*	P value^†
Male : female	72 : 60	20 : 19		0.719
Age (years)	66.0 [23.0]	67.0 ± 19.0	–0.499	0.618
Worrisome periampullary diverticulum score
Score = 0	121 (91.7)	28 (71.8)		0.000
Score = 1	7 (5.3)	4 (10.3)
Score = 2	4 (3.0)	7 (17.9)
Presence of papilla bulging	19 (14.4)	13 (33.3)		0.008
Presence of far distal CBD stone	22 (16.7)	3 (7.7)		0.163
Location of the major papilla other than the descending duodenum	10 (7.6)	6 (15.4)		0.206
CD angle (°)	40.9 ± 15.7	35.2 ± 15.6	2.011	0.655
Common bile duct diameter (mm)	7.0 [3.6]	6.4 ± 4.0	–1.112	0.266
Aspartate aminotransferase (g/dL)	109.0 [195.0]	85.0 ± 186.0	–0.300	0.764
Alanine transaminase (g/dL)	138.5 [213.8]	135.0 ± 390.0	–0.131	0.896
Total bilirubin (g/dL)	2.3 [3.7]	1.4 ± 2.9	–0.911	0.362

Values are given as n (%), median [interquartile range] or mean ±SD or mean ± SD. P values < 0.05 were considered statistically significant.

*Student’s t-test and Mann–Whitney U test were used for the continuous variables.

†

Chi-square test and Fisher’s exact test were used for the nominal variables and linear by linear association test for the ordinal variables.

CBD, common bile duct; CD, choledochoduodenal.

In the group with cannulation difficulty, the worrisome PAD score was significantly higher (P ≤ 0.000) and the papilla bulging was more frequently seen (P = 0.008) than the group without cannulation difficulty. The endoscopic findings of the patients based on the ERCP records are shown in Table 2.

Table 2.

ERCP findings

ERCP findings	n (%)
Biliary stone	92 (53.8)
Cholangitis	40 (23.4)
Suspected spontaneous passage of a biliary stone	30 (17.5)
Malignant stricture (known or suspected)	20 (11.7)
Suspected sphincter of Oddi disfunction	12 (7.0)
Benign biliary stricture	7 (4.1)
Postoperative biliary stricture or leakage	7 (4.1)
Normal	8 (4.7)
Other conditions*	4 (2.3)

*Other conditions included autoimmune pancreatitis, suspected primary sclerosing cholangitis, and pancreatic intraductal papillary mucinous neoplasm.

The inter-observer agreement between the two radiologists was good (k = 0.775, 95% confidence interval [CI] = 0.695–0.833) for the CD angle and excellent for the CBD diameter (k = 0.956, 95% CI = 0.927–0.971).

Multivariate logistic regression analysis

The multivariate logistic regression analysis demonstrated that a higher worrisome PAD score, presence of papilla bulging, smaller CBD diameter, location of the major papilla other than the descending duodenum, and smaller CD angle were statistically relevant factors for cannulation difficulty (Table 3).

Table 3.

Multivariate logistic regression analysis of the risk factors for cannulation difficulty.

Variables	P value	Odds ratio	95% CI
Worrisome periampullary diverticulum score	0.001
Score 1	0.262	2.466	0.509–11.942
Score 2	0.000	16.653	3.673–75.497
Presence of papilla bulging	0.000	7.597	2.639–23.989
Far distal CBD stone	0.079	0.245	0.051–1.179
CBD diameter	0.049	0.854	0.541–13.313
Location of the major papilla other than the descending duodenum	0.017	5.051	1.329–19.201
CD angle	0.015	0.966	0.939–0.993

P values < 0.05 were considered statistically significant.

CBD, common bile duct; CD, choledochoduodenal; CI, confidence interval.

Decision-tree analysis

The decision-tree model is shown in Fig. 6. The worrisome PAD score was the strongest predictive variable and was seen as the first split in the tree. The CD angle, presence of a bulging papilla, and the CBD diameter defined further splits of the tree. The terminal nodes at the bottom of the tree demonstrated the seven mutually exclusive risk groups. All patients met the criteria of one of the seven groups.

Fig. 6.

Decision-tree analysis model for prediction of cannulation difficulty. CBD, common bile duct; CD, choledochoduodenal; PAD, periampullary diverticulum.

The subgroup 1 included six patients who had a worrisome PAD score 2 and a CD angle ≤ 41.865° (as in the figure). In this group, all patients underwent a difficult cannulation. Conversely, the subgroup ‘7’ included 25 patients who had a worrisome PAD score of 0 or 1, no papilla bulging, a CD angle > 18.275°, and a CBD diameter > 8.090 mm. None of the patients in this group experienced cannulation difficulty.

The model demonstrated an overall predictive accuracy of 82.5%, sensitivity of 26%, and specificity of 99%. The positive predictive value was 91% and the negative predictive value was 82%.

Discussion

The failure rate of biliary cannulation can be as high as 20%, even for experienced endoscopists (2,4). Repeated manipulation of papilla leads to pancreatitis and cholangitis. When the initial attempt with conventional methods fails, precut sphincterotomy is considered, which was reported to increase the risk of post-ERCP pancreatitis, bleeding, and perforation (5). Furthermore, cannulation failure leads to further procedures with a higher morbidity, such as transhepatic intervention or surgery (9,23–25). Therefore, it is crucial to successfully perform ERCP with utmost therapeutic effectiveness and with the least patient morbidity and mortality.

The incidence of PAD is reported to be 1%–23% on autopsy series and the prevalence increases with age (13,26). There have been many studies regarding the relationship between the presence of PAD and cannulation difficulty. A large prospective study of 2458 patients reported that the cannulation success rate was significantly higher in the patients without PAD and the sphincterotomy failure rate was higher when the papilla was located deep within the diverticulum (17). CT is known to be useful in the evaluation of the PAD structure, and the neck of the diverticulum can be well visualized in multiplanar reformatted images (27). In particular, CT has an advantage over ERCP in evaluating the size, contour, and internal content of the PAD. In our study, the worrisome PAD score was calculated by adding up the points given to radiologically defined type I PADs and PADs > 1.5 cm. The higher score was the strongest predictive factor for longer cannulation time. There are several possible explanations for the cannulation difficulty caused by PAD. First, if the papilla is located deep inside the large PAD, it may take a long time to detect the papilla opening (11,16). Second, the papilla can be floppy when it is located on the edge of the PAD (11). Third, the PAD may cause mechanical compression or distortion of the distal CBD, inflammation within the poorly draining diverticulum, and sphincter of Oddi spasm, which can further hinder the successful biliary cannulation (16,17,26).

The presence of papilla bulging was a predictive factor for calculation difficulty. CT can detect a bulging papilla and identify various underlying pathologic conditions using 3D reconstruction images (19,20). In the presence of papilla bulging, it is more difficult for the sphincterotome to enter the papilla and even if it enters, further cannulation can still be problematic (2).

A previous study reported that the typical angle of the duodenoscope was significantly related to the cannulation success (28). However, there was no previous study concerning the angle between the bile duct and duodenum, which we named the CD angle. We demonstrated the association between the smaller CD angle and increased cannulation difficulty. During ERCP, endoscopists should place the duodenoscope or catheter in an optimal position to visualize the papilla and advance further into the ampulla to reach the CBD (2). If the angle between the distal CBD and duodenum is acute, the catheter needs to enter the CBD in a direction almost opposite to the direction in which it traveled through the duodenum, which may lengthen the cannulation time.

A smaller CBD diameter was a predictive factor for cannulation difficulty. A previous study mentioned that in patients with a large CBD diameter due to long-standing functional obstruction, the intramural segment of the ampulla may be widened due to laxity of the biliary sphincter (29). In contrast, the patients with a normal CBD diameter and an intact sphincter function may have a narrower intramural segment (29). This may be a possible explanation for the result of our study.

The location of the major papilla other than in the descending duodenum was associated with difficult cannulation. The major papilla is mostly located in the descending duodenum and less commonly located in the junction between the descending and horizontal duodenum, or in the horizontal duodenum (30). There are several reasons why the atypical position of the major papilla can make cannulation difficult. First, if the major papilla is located distal to the descending duodenum, the catheter needs to navigate longer distance to reach the papilla (2). In addition, because the papilla is not located in the usual position, it is more difficult to localize it. Finally, the atypical position and angle of the duodenoscope may further complicate the cannulation procedure (28).

Although the sensitivity of the decision-tree model was low, the specificity and positive predictive value were very high, and the negative predictive value was substantially high. By using the prediction model, the endoscopists can classify patients according to anticipated cannulation difficulty with high probability. If the cannulation is predicted to be troublesome, they can provide the patients with more detailed explanations about possible postprocedural complications and prepare additional equipment or specialized techniques in advance. In addition, they may keep a second-hand supervisor nearby or transfer the patient to a referral hospital for further treatment options.

There are a few limitations in our study. First, the study was retrospective in nature and the anatomic factors, such as the PAD type or bulging papilla were not consistently confirmed during ERCP. Therefore, it was impossible to calculate the degree of agreement between the CT image findings and the endoscopic findings. Second, ERCP procedures were performed by three different endoscopists. However, considering that >350–400 ERCPs are needed to achieve competency in selective biliary cannulation, all endoscopists in our study had sufficient experience and skill in ERCP (2,31).

In conclusion, the decision-tree analysis model based on CT imaging findings showed a high accuracy for predicting cannulation difficulty. This model may be helpful for making preprocedural strategy before performing ERCP.

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Na Yeon Han

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