Anat Cell Biol 2020; 53(1): 8-14
Published online March 1, 2020
Copyright © Korean Association of ANATOMISTS.
Bikramaditya Swain, Ranjan Kumar Sahoo, Kamal Kumar Sen, Manoj Kumar G, Shylendra Singh Parihar and Roopak Dubey
Department of Radiodiagnosis, Kalinga Institute of Medical Sciences (KIMS), KIIT University, Bhubaneswar, India.
Correspondence to: Ranjan Kumar Sahoo. Department of Radiodiagnosis, Kalinga Institute of Medical Sciences (KIMS), KIIT University, Bhubaneswar, Odisha 751024, India. Tel: +91-6747105300, Fax: +91-6747105300, Email: firstname.lastname@example.org
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Intrahepatic and extrahepatic anatomical knowledge is essential for pre procedural planning of liver transplantation, liver resection, complex biliary reconstruction and radiological biliary tree intervention. Indian data of biliary anatomy and its variation is scant in literature. The aim of our study is to find out the prevalence of common and uncommon pattern of biliary tree anatomy in magnetic resonance cholangiopancreatography (MRCP) in our population. A total of 1,038 cases of MRCP of population of Odisha were obtained from Picture Archiving and Communication System of the department and were reviewed by two senior radiologists for anatomical pattern and variations. The typical and most common pattern of right hepatic duct (RHD) branching was seen in 72.8% cases. The most common variant of RHD was trifurcation pattern of insertion of right anterior sectoral duct (RASD), right posterior sectoral duct and left hepatic duct (LHD) forming common hepatic duct (CHD) in 11.3% of cases. The common trunk of segment (SEG) II and III ducts joining the SEG IV duct was the most common LHD branching pattern in 90.3% of cases. The most common pattern of cystic duct was posterior insertion to middle third of CHD (42.8%). MRCP is the non-invasive imaging modality for demonstration of biliary duct morphology to prevent iatrogenic injury during hepatobiliary intervention and surgery.
Keywords: Magnetic resonance imaging, Anatomic variation, Bile ducts, Intraheaptic, Cholangiography
Knowledge of complex biliary anatomical variation is crucial before hepatobiliary intervention such as laparoscopic cholecystectomy, living donor liver transplantation, hepatic tumor resection and therapeutic biliary drainage [1,2]. MRCP is the preferred non-invasive imaging modality for biliary anatomy evaluation as it is safe and is not associated with ionising radiation. High resolution cross-sectional, two dimensional and three dimensional (3D) projection imaging is possible for detailed anatomy which is comparable to endoscopic retrograde cholangiography (ERCP) and intraoperative cholangiograms [3,4]. The individual biliary channels run parallel to portal veins. Liver is divided into eight functional independent segments (SEGs) (I to VIII SEG) based on Couinaud classification. SEGs VI and VII are drained by right posterior sectoral duct (RPSD) which is oriented horizontally and SEG V and VIII are drained by vertically oriented right anterior sectoral duct (RASD). The right hepatic duct (RHD) is formed by union of RPSD and RASD. The RPSD joins the RASD from left medial aspect. Sectoral ducts of SEGs II, III and IV fuse to form left hepatic duct (LHD). The bile duct from caudate lobe drains to origin of right or LHD. RHD and LHD join to form common hepatic duct (CHD). The cystic duct (CD) usually joins the middle third of CHD after the union of RHD and LHD. About 58% of population shows normal biliary anatomy .
We carried out the study to look for the normal and variation of biliary ducts anatomy with their prevalence in our state, Odisha which is located in eastern part of India with Asian race of population.
The present study was a retrospective analysis of 1,038 cases of MRCP done in our institution from January 2016 to July 2019, which included 532 males and 506 females with the age range of 2 to 96 years. The studies were done in 1.5T magnetic resonance imaging (MRI) machine (1.5T system, GE Signa; GE Healthcare, Fairfield, CT, USA) using body coil for the acquisition of the images. MRCP were done utilizing time of relaxation (TR)-8,000 ms; time of excitation (TE)-800 ms; flip angle 90 degrees; field of view (FOV) 250–300 mm; 40 mm thick oblique coronal slices at 0.4-mm interval on breath hold. Respiratory gated 3D images were obtained utilizing TR-1,204 ms; TE-650 ms; flip angle 90 degrees; FOV 280. The 3D MRCP, coronal and axial MRI images extracted from Picture Archiving and Communication System were analyzed by two senior radiologists. Our classification of RHD variations was similar to Huang et al.  (Table 1). However, we added another type-VI which included as unclassified type. The LHD variation was similar to Cho et al. . We classified the CD variation according to direction and site of CD joining the CHD (Table 1) [6,7]. The low insertion of CD indicates the joining of CD with distal third CHD and proximal insertion of CD indicates the joining of CD with proximal third CHD close to primary confluence. The data was analyzed using IBM SPSS Statistics for Windows, Version 22.0 (IBM Co., Armonk, NY, USA). Values were expressed in percentages. The study was carried out after institutional research board and ethical committee approval.
Total 1,038 MRCP were studied. The mean age of cases was 48.98±17.26 year. A 532 cases (51.3%) were males while 506 cases (48.7%) were females. In the group of right sided biliary duct variation (according to Huang classification), type-I (typical) branching pattern was noted in 756 cases (72.8%), type-II in 117 cases (11.3%), type-III in 100 cases (9.6%), type-IV in 59 cases (5.7%), and type-V in 4 cases (0.4%) (Fig. 1) . Type-1, 2, and 3 LHD branching pattern (according to Cho et al. ) were noted in 937 cases (90.3%), 20 cases (1.9%), and 80 cases (7.7%) respectively (Fig. 2). One unclassified type was seen where the SEG II duct and common duct of SEG III and IV join the RHD separately (Fig. 2) . We classified the types of CD variation as mentioned in the Table 1 [6,7]. CD variations were seen with anterior spiral insertion in 140 cases (13.4%), medial insertion in one case (0.1%), posterior spiral insertion in 444 cases (42.7%), right lateral insertion in 408 cases (39.3%), low medial insertion in 35 cases (3.4%), low lateral parallel insertion in one case (0.1%), proximal insertion of CD in 7 cases (0.7%), drainage of CD into RHD in one case (0.1%) and to RASD in one case (0.1%). Right anterior accessory duct was seen draining into anterior aspect of CHD in one case (0.1%) (Figs. 3 and 4).
The typical right hepatic biliary anatomy has been reported to occur in 55% to 67% in larger population studies [9,11]. We found about 72.8% of typical right biliary anatomy in our study. No complete classification of biliary anatomy is present. Different classifications of biliary anatomy have been proposed as there are many variation of biliary anatomy . It is essential to know the complex SEGal hepatic biliary anatomy for staging and localization of intrahepatic liver neoplasms or bile duct tumors, hepatic lobectomy or segmentectomy, complex interventional biliary procedures and before cholecystectomy to prevent complications due to unwanted biliary duct injury . The most common biliary duct branching variation was trifurcation pattern (Type-II, 11.2%) followed by union of RPSD to LHD (Type-III, 9.7%) in our study. This finding is comparable to few of the previous studies [6,8,11,18]. In rest of the studies as mentioned in the Table 2, Type-III RHD variation was more common than type-II pattern [7,9,10,12,13,14,15,16,17]. Above two variations have no surgical significance except in left hepatectomy, where ligation of RPSD may cause biliary cirrhosis of SEG VI and VII .
Type-1 (90.3%) was the most common type LHD confluence pattern in which the common channels of SEG II and III joins the SEG IV biliary duct of liver. Type-2 and 3 are seen in 1.9% and 7.7% of population respectively. Type-1 (one) pattern was seen in 59% to 78% population in previous studies [8,12,15,17]. However, type-3 pattern of LHD was the second most common pattern in our study unlike previous studies.
The CD shows extreme variable course and levels of union with CHD. No standard classification of CD variation was described in literature. CD anatomy can be evaluated by ultrasonography, computed tomography, direct cholangiography, MRCP and cholescintigraphy. MRCP provides better imaging evaluation of CD noninvasively. Anatomic variants of the CD are common and are usually of no clinical significance . However proper interpretation of CD anatomy and variation is required to understand the disease process, prevent the iatrogenic injury and for medicolegal purpose in case of post-operative complications . In our study, we classified the CD variation into 9 types (type-A to I). The most common type of CD pattern was posterior insertion of CD over middle third of CHD (42.8%) followed by right lateral insertion (39.3%) in our study. Sarawagi et al.  found posterior CD insertion as the most common variant in 20.2% cases followed by medial spiral insertion of CD (16.1%). Surekha et al.  found medial insertion of CD variation as most common variation in 10% to 17% cases. Hussein et al.  found right lateral insertion in 75% of cases out of 238 cases. We did not find any case of double CDs, short CD or any fusiform dilation of CD in our study. No accessory duct from liver to gall bladder was seen.
In addition to normal biliary classification, many unclassified complex anatomy cases have been found in different studies. We found three unclassified pattern. In first case, CD is seen draining into RASD. Right anterior accessory duct is seen joining on anterior aspect of CHD in second case. Left SEG II duct and common duct of SEG III and IV were seen joining the RHD separately in third case (Figs. 2 and 4).
This study included larger number of cases and reported anatomical pattern and variation of right, left biliary ducts and CD in population of Odisha which has not been reported before. Most of the recent literatures included part of hepatic biliary anatomy with less number of cases. We found complex unclassified new anatomical variation of biliary channels which were reported rarely.
Limitation of our study was that there was no comparison of the MRCP finding with intraoperative cholangiogram. Thin collapsed segmental biliary duct without bile may not be seen in non-enhanced MRCP. Multicentre larger study is required to determine the prevalence of biliary tract anomaly more accurately in India.
In conclusion, in summary, atypical branching patterns of right hepatic biliary channels were found in 27.2% of MRCP belonging to population of Odisha. The two most common variations of right hepatic biliary anatomy were trifurcation pattern of insertion of the RASD, RPSD, and LHD followed by RPSD draining directly into the LHD. Common confluence of SEG II, III and IV ducts joins together to form LHD was the common LHD anatomical variation. Posterior spiral insertion of CD with middle third CHD was the most common pattern of CD union with CHD. Knowledge of intrahepatic and extrahepatic biliary variations is useful for planning of hepatobiliary surgery and radiological biliary intervention.