Dilatation of CBD can be caused by diverse etiologies either benign like choledochocholithiasis, CBD stricture, and papillary stenosis or malignant like cholangiocarcinoma and pancreatic head mass . TUS, in skilled hands, can diagnose biliary obstruction via demonstration of biliary dilation. TUS may potentially identify the pancreatic mass or hepatic metastases as well as allowing needle biopsy of these lesions . However, it has a relatively poor sensitivity for the detection of pancreatic neoplasms compared with other techniques .
Both EUS and MRCP are excellent modalities with comparative accuracy for evaluation of pancreaticobiliary disorders. Multiple studies have shown high diagnostic performance of them with no significant difference in the diagnostic yield [13, 14]. On the other hand, some demonstrated that the diagnostic yield of MRCP decreases in the presence of dilated CBD and small CBD stones . Therefore, in these situations, EUS has a favorable diagnostic yield. So, we prospectively evaluated the role of EUS in patients with dilated CBD and inconclusive TUS.
In the present study, TUS successfully identified patients with cholelithiasis but failed to diagnose 60 patients with dilated CBD. Moreover, most of patients with bulky pancreas on TUS revealed to be definite pancreatic mass on further EUS evaluation.
This was in accordance with Songür et al.  who investigated 90 patients with dilated CBD of unexplained cause on US with EUS, and correct diagnosis was achieved in 92% cases with EUS.
Surinder et al.  retrospectively analyzed 40 patients with dilated CBD on MRCP without obvious etiology referred for further evaluation by EUS. The EUS diagnosis was CBD stones in 15 (37.5%), with largest size of CBD stone being 9 mm, mass in CBD in 2 (5%), benign biliary stricture in 2 (5%), and biliary stricture with underlying chronic pancreatitis in 1 (2.5%) patient respectively. EUS examination revealed normal CBD in 20 (50%) patients, and two of these patients had periampullary diverticulum.
In our study, the sensitivity and specificity value for malignant obstruction detected by EUS was 100% and 86.36%, respectively, with positive predictive value of 92.68%, negative predictive value of 100%, and overall accuracy of 95%. This was in agreement with Chen et al. study, in which the sensitivity and specificity value for malignant obstruction detected by EUS was 97.5% and 97.6%, respectively, with positive predictive value of 95.1%, negative predictive value of 98.8%, and overall accuracy of 92.9% .
Also, Maluf-Filho et al.  showed that the sensitivity and specificity value for malignant stricture detected by EUS were 96.6% and 90.6%, respectively, with positive predictive value of 90.3%, negative predictive value of 96.7, and accuracy of 93.4%, while Thomas Rösch et al.  showed that the sensitivity and specificity for diagnosis of malignancy in the 50 patients were as follows: 85%/75% for ERCP/PTC, 85%/71% for MRCP, 77%/63% for CT, and 79%/62% for EUS.
Moreover, in Hauke et al.  who compared different diagnostic tools for detecting bile duct malignancy, it has accuracy rates of 91% (ERCP/IDUS), 59% (ETP), 92% (IDUS + ETP), 74% (EUS), and 73% (CT), respectively.
In our study, the sensitivity and specificity values for benign strictures detected by EUS were 100% and 98.4%, respectively, with positive predictive value of 90%, negative predictive value of 100%, and accuracy of 98.33%. This was in agreement with Chen et al.  who found that the sensitivity and specificity value for calcular obstruction detected by EUS was 92.9% and 97.7%, respectively, with positive predictive value of 92.9% and negative predictive value of 97.9% and overall accuracy of 92.9%. Also, the overall accuracy of EUS was 100% for benign obstruction.
Alhawarey et al.  demonstrated that EUS, as diagnostic tool, has sensitivity, specificity, PPV, NPV, and accuracy of 100%, 92.8%, 93.7%, 100%, and 96.5% respectively.
Also, in Meeralam et al.  meta-analysis of the diagnostic accuracy of EUS compared with MRCP in detecting choledocholithiasis, the overall diagnostic odds ratio of EUS was significantly higher than the one with MRCP (162.5 vs. 79.0, respectively; P = .008).
In our study, the sensitivity and specificity values for malignant stricture detected by MRI were 82.14% and 25% respectively with positive predictive value 7of 9.31 and accuracy of 69.4%. On the other hand, for benign etiologies, MRI showed 33.33% sensitivity and 96.97% specificity with positive predictive value of 50% and accuracy of 91.67%. EUS supported correct diagnosis in 57 patients (95%: CI 86.08% to 98.96%), while MRI did it in 36 patients (69.44%: CI 51.89% to 83.65%). This was in line with Songür et al.  who investigated 90 patients with dilated CBD of unexplained cause on US by EUS, and correct diagnosis was achieved in 83 cases with EUS. Maluf-Filho et al.  EUS supported correct diagnostic hypothesis for pancreatobiliary malignancy in 40:46 patients (87.0%; CI 77.2–96.7), while CT did in 31:36 patients (67.4%; CI 53.8–80.9).
In our cohort, only 43 (71.7%) patients needed ERCP for management of obstructive jaundice, sparing 17 patients (28.3%) unnecessary invasive procedures. This was in line with Patel et al.  study where EUS ruled out choledocholithiasis in 38 patients (48.7%). Two of them were found to have choledocholithiasis on follow-up. The sensitivity, specificity, and positive and negative predictive value of EUS for detecting choledocholithiasis were 93.9%, 97.3%, 96.9%, and 94.7%, respectively. Unnecessary ERCP was avoided in 57.7% of the patients by using the EUS-first approach.
Our study has its own limitations. This is a single-center experience, but it has the privilege of prospective evaluation of patients. So, multicenter studies with cost effective analysis are recommended. We believe that the malignant life-threatening etiologies of biliary obstruction should not be missed; it is of utmost importance that those who do not have a pathologic cause of biliary dilatation are not subjected to unnecessary invasive/semi-invasive evaluation.
In conclusion, EUS is a minimally invasive method with low incidence of complications with high diagnostic accuracy in patients with dilated CBD and normal MRCP.