The impact of the anatomy and pathology of Vaterian papillae and biliary tree pathology on the choice of access technique (cannulation difficulties, sphincterotomy technique, two-step access) and adverse events has not been fully explained. Few studies have examined all of these factors together [12]; most analyses have focused only on the relationship between papilla shape and cannulation difficulty and excluded deformed papillae, altered CBD anatomy and PADs[1,2,6,9,16,17,18], while other authors only examined access techniques without considering anatomy [5,7,9]. Therefore, in our study, we additionally included infiltrated ampullae of Vater (according to a modification of Haraldson's classification), the extent of biliary tree obstruction and the presence of PADs. This approach can improve the understanding of the relationship between difficulties during access and other factors, not only the shape of the papillae. Knowledge regarding this subject is important because it can facilitate the training process, enable proper selection of endoscopists (according to their level of experience) and ensure that the access technique (depending on the papilla shape and biliary tree pathology) has the lowest risk of complications. Difficult cannulation: Our results confirmed that the degree of difficulty during cannulation depends not only on the shape of the papillae but also on the level of bile outflow blockade. Taking other factors into account answers the question posted by Sinha as to why flat papillae were difficult to cannulate in Haraldson's studies [2,8]. According to the results of this study, cannulation was difficult in 56.9% (58/102) p=0.0002, of patients with deformed (type 4) papillae, 46.4%(162/349; p=0.0011 of patients with distal biliary tree flow obstruction and 49.5% (46/93)(p= 0.0407 of patients with medial biliary tree outflow obstruction. Therefore, it should be recommended that procedures in these patients be performed by experienced endoscopist In contrast, for patients with a low risk of cannulation difficulty, such as those with classic (type 1) papillae (34.3%; 163/475) (p=0.0014), choledocholithiasis (31.7%; 145/458) (p<0.0001), and perhaps even PAD (29.4%; 60/204) (p=0.001), this issue requires more detailed analysis; it may be possible for endoscopists to treat these patients during the learning process under supervision. Due to the lack of a uniform classification system for determining the shape of papillae and differences in the frequency of use of guidewires for various kinds of sphincterotomy and two-step access, comparing the obtained results with those of other studies is challenging. For example, apart from Haraldson, his classification system has been used only for analysis by Chen, Estela and Balan [6,11,12]. In a multicenter analysis, Haraldsson's team enrolled 1401 patients and reported that cannulation was more difficult in patients with small (type 2) papillae (52%; 95% CI, 45%-59%) and protruding (type 3) papillae (48%; 95% CI, 42%-53%) than in those with classic (type 1) papillae [2]. Chen analyzed 286 patients and obtained similar results. Small (type 2) papillae (OR 7.18, p = 0.045) and protruding (type 3) papillae (OR 7.44, p = 0.016) were more difficult to cannulate than classic (type 1) papillae [11]. A similar conclusion was reached by Balan, who showed that significantly more cannulation attempts (mean value of 5.5 attempts, p = 0.00108) and more time (mean value of 5.6 minutes, p = 0.00181) were needed for patients with small (type 2) papillae [12]. In the present study, these relationships were not significant (40.3%; 127/315; p= 0.73; OR 1.05; p=0.73); however, two-step access was used significantly more frequently for patients with small (type 2) papillae (17.8%; 56/315; p= 0.032; OR 1.49; p=0.032). Indirectly, these findings suggest difficulties in deep cannulation of the target duct in this group of patients. However, it should be emphasized that comparing these data with those of other studies is problematic because of the different definitions of type 2 papillae and leakage of the distal CBD with an altered anatomy. Other factors that may explain these differences are the frequency with which a guidewire was used and the use of different precut incision techniques. The Haraldson group used guidewires in approximately 50% of patients; classic access was impossible, and the precut technique was used in only 9% of patients [2]. In contrast, we used guidewires in more than 90% of patients, NPCs in 38.7%(43/111) p<0,0001 (OR 3.54 p <0.0001) of patients with protruded (type 3) papillae and CPC in 42.2%(43/102) p=0,017 (OR 1,65 p = 0,0183) of patients with deformed (type 4) papillae. Other results were published by Estela, who, in the analyzed group (230 patients), difficult cannulization was more common in type 3 (3.66%, 95% CI 2.49-5.84), type 4 (3.21%, 95% CI 1.82-5.75), and type 2 (1.95%, 95% CI 1.15-3.20) patients than in type 1 patients. These results are partially consistent with ours, but we did not confirm any difficulties during cannulation of type 2 papillae [6]. The differences may result from differences in the classification and access technique used. The next factor that could explain the differences was the exclusion criteria. Haraldsson, Chang, Balan and Estella excluded patients with tumors or other causes of deformity of the papillary region (meaning that approximately 10% of patients treated daily by ERCP were excluded). [2,6,11,12] In our study, according to the modified Haraldson classification, all patients with deformed papillae were classified as having type 4 papillae. In our series, this group had the highest probability of experiencing a difficult cannulation (56.9%; 58/102; p=0.0002; OR 2.19, p=0.0002). Most of our patients in group 4 had cancer-related deformed papillae. In this way, a similar result was presented by Chen, who reported that the presence of neoplasia was related to difficulty in cannulation (OR 4,45 p=0,014) [11]. Additionally, Chen reported that type 1 papillae required significantly less time for cannulation (56.78% of the patients could be cannulated within 5 minutes) and had the lowest cannulation failure rate (1.69%) 1,55 (1,19-2,02) [11]. Similarly, our study revealed that the risk of cannulation difficulties in patients with type 1 papillae was significantly lower (34.3%; 163/475; p= 0.0014; OR= 0.66; p= 0.0014). However, differences from Chen’s research exist in terms of PEP risk factors. We did not find a relationship between papilla shape and the risk of PEP. In contrast, Chen reported that type 2 papillae were correlated with a greater percentage of PEP (20%, p = 0.020). This difference may be due to Chen’s application of endoscopic papilla balloon dilatation (OR for PEP 4,51) [13], whereas we used two-stage access in 17.8% (56/315; p=0.032; OR 1.49; p= 0.032) of patients with type 2 papillae, which can reduce the risk of PEP. These results may justify the early use of a two-stage procedure in patients with type 2 or 4 papillae. The next factor analyzed was the presence of PADs, which may increase the risk of difficulties and complications [11,14]. However, the presence of a weak point in the duodenal wall can also facilitate access to the biliary duct. This relationship was also found in the present study, which showed that the presence of PADs made cannulation easier in 29.4% (60/204) of patients (p= 0.001; OR=0.57, p=0.01). Interesting data in this regard were presented by Mu in a meta-analysis [15]. In previous studies, the presence of a PAD was related to difficult cannulation (RR=1.46, 95% CI=1.27-1.67; p<.00001); however, within the last 20 years, these relationships were not statistically significant (RR=1.16, 95% CI=0.96-1.41; p=0.12). This is probably a consequence of the development of equipment and cannulation techniques. Additionally, in Mu’s study, PAD was also associated with a high risk of PEP (RR=1.32, 95% CI=1.10-1.59; p=0.003), perforation (RR=1.73, 95% CI=1.06-2.82; p=0.030), and bleeding (RR=1.48, 95% CI=1.13-1.93; p=0.005) [15]. We did not observe this relationship, and these differences are likely a consequence of the authors’ significantly less frequent use of NPC (9.3%; 19/204; p=0.0004; OR=0.41; p=0.0006) in PAD patients. Many other classifications of Vaterian papillae have been created but do not include patients with PADs; therefore, it is impossible to compare these results with those of other studies [16,17,18,19]. Access technique: We confirmed that the type of papillae, presence of PAD and biliary tree pathology have an impact on the technique chosen for performing sphincterotomy. CS was possible significantly more frequently in patients with type 1 papillae (47.4%; (259/475; p= 0.0155; OR 1.36; p= 0.0156); in patients with PAD (54.4%; (117/204); p=0.028; OR 1.41; p=0.028); and in patients with choledocholithiasis (54.1%; (248/458); p=0.0341; OR 1.31; p=0.0341). CPC was chosen significantly more often in patients with type 4 papillae (42,2%; 43/102; p= 0.0171; OR 1.65; p=0.0183), and NPC was chosen more often in patients with type 3 papillae (38.7%; 43/111; p<0.0001; OR 3.54; p<0.0001). Only two studies have analyzed the sphincterotomy technique chosen in relation to papilla shape; unfortunately, other papilla shape classifications were used in these studies [16,20]. The Canena (2021) classification includes 7 types: type 1 (flat), type 2A (prominent with <1 fold), type 2B (prominent and >2 folds), type 2C (bulging), type 3A (interdiverticular), type 3B (diverticular border type), and type 4 (unclassified). The authors analyzed 361 patients who underwent only needle knife fistulotomy (NKF). According to multivariate analysis, flat (type 1) and prominent (< 1-fold) (2B) papillae were risk factors for difficult cannulation, and types 2B, 3A and 3B were associated with the lowest cannulation rates post-NKF [16]. In our study, the preferred technique for all patients with PAD was CS (54.4%; 117/204;p=0.028; OR 1.41; p=0.029), and we used NPC significantly less often (9.3%; 19/204; p=0,004;OR 0.41;, p=0.0006). In contrast, in Canena’s study, NKF was used significantly more often for type 2c papillae (similar to type 3 in Haraldsson’s classification). This finding is consistent with our results, as we used NPC significantly more often in patients with type 3 papillae (38.7%; 43/111; OR 3.54; p< 0.0001). A study conducted by Horiuchi in 2007 analyzed 86 patients. The effectiveness of the three-type precut technique on the basis of papilla shape was assessed: for small (Haraldsson type 2)- trans pancreatic (CPC),for large (Haraldsson type 1) - needle knife precut (NKP) , and for swollen (Haraldsson type 3) needle knife fistulotomy (NKF) . Successful access to the biliary tree was achieved in 96%, 90%, and 100% of patients, respectively. The overall complication rate was 4.7% (4 of 86) (2 patients with mild bleeding and 2 with mild pancreatitis) [20]. These criteria for choosing the ES technique agree with our own technique for swollen (Haraldson type 3) papillae, for which the most common technique was NPC (38.7%; 43/111; p<0,001; OR 3.54; p< 0.0001). In contrast, for the small papillae (Haraldson type 2) in our study, the CPC technique for sphincterotomy was used significantly less often (27.0%; 85/315; OR=0.72; p = 0.0287). The above comparison highlights the lack of uniform rules for the use of various access techniques according to the existing anatomy; therefore, to reach a consensus, this issue requires further research. The limitations of the present study include its single-center nature and the fact that the analyzed procedures were performed by one operator. Therefore, there is a risk of bias in the technique of assessing the shape of the papillae and the selection of access techniques. Another limitation was the low number of participants in each group (with different anatomies of the bile ducts) after division according to the access technique used. The existing number of patients made it impossible to perform a statistical analysis of the relationships between the detailed anatomy and access technique used and side effects.