B SAFE: Anatomical Safety Landmarks in Laparoscopic Cholecystectomy

Calots_Triangle_Ozimo_Gama

INTRODUCTION

It is crucial to have a thorough knowledge of the relevant anatomy as the procedure is performed in an area adjacent to many vital structures (portal vein, hepatic artery and extrahepatic biliary tract). Furthermore, the surgeon needs to be mindful of common anatomical variations, and the anatomical distortion due to pathological processes (e.g., acute/chronic cholecystitis). Safe execution of LC requires clear understanding of following anatomical terms/landmarks.

Hepatocystic Triangle

This is an area on the under surface of the liver on the right side of the hepatic hilum. It has CHD on the medial side, cystic duct caudally, and liver under surface cranially. This triangle contains the cystic artery, a variable portion of right hepatic artery, the cystic lymph node, lymphatics, and a variable amount of fibro-fatty connective tissue.

Clinical significance: This is the target area for dissection during LC. This triangle is different from Calot’s triangle where the cystic artery forms cephalad boundary instead of the liver surface. In literature, these terms have been used interchangeably but in present review only the term “HC triangle” has been used to maintain uniformity as the actual dissection takes place in this triangle, not in Calot’s triangle; The cystic lymph node often lies superficial to the cystic artery and acts a landmark to locate this artery. The artery should be divided on the right side of this lymph node close to the gallbladder to avoid injury to the right hepatic artery. This landmark is quite useful in difficult cases. This area may be affected by the inflammatory process during acute or chronic cholecystitis, and it may appear thick, fibrotic, or scarred, which may create difficulty in anatomical identification and/or dissection.

Cystic Plate

This is a flat ovoid fibrous sheet located in the gallbladder bed. It is a part of sheath/plate system of the liver. It is continuous with liver capsule of segment 4 (medially) and segment 5 (laterally). Postero-medially towards the hepatic hilum, it narrows to become a stout cord like structure that is continuous with the sheath of the right portal pedicle.

Clinical significance: With gallbladder in-situ, the cystic plate is not visible as it is covered by the gallbladder. It is exposed as whitish/greyish structure once the gallbladder is dissected off of the liver. It is important to expose the lower part of the cystic plate while achieving the CVS as discussed subsequently in this article. The CVS is considered incomplete without this exposure as an anomalous duct (e.g., right posterior sectional duct) may exit the liver or an anomalous right hepatic artery may enter the liver in this area. These structures may be at risk of injury if not identified properly. While the fundus and most of the body of the gallbladder remains closely adherent to the cystic plate, a layer of loose areolar tissue between the gallbladder wall and the cystic plate thickens towards the hilum. It is important to remain close to the gallbladder wall while dissecting it off the liver leaving behind the areolar tissue that is attached to the cystic plate while dissecting the neck of the gallbladder and the cystic duct. It is important not to breach the cystic plate while dissecting the gallbladder off the liver. Breaching the cystic plate during this step may cause two problems. First, there might be troublesome bleeding from liver parenchyma, especially if the terminal tributaries of the middle hepatic vein (which lie in this location) are injured. Second, sub-vesical bile ducts (coursing superficially close to gallbladder fossa) may be injured, causing a postoperative bile leak . Such a breach is more likely to occur in chronic cholecystitis where the gallbladder may be densely adherent to the underlying liver without distinct dissection planes. In chronic cholecystitis with a small and contracted gallbladder, the longitudinal length of the cystic plate from the fundus to its attachment with right portal pedicle sheath becomes short. Without appreciating this pathologic shortening, the surgeon may enter into the right portal pedicle sheath soon after the dissecting the fundus/body of the gallbladder if the fundus first technique is attempted. This may cause injure to the right portal pedicle structures causing serious VBI.

Rouviere’s Sulcus

This sulcus is 2-5 cm long and is present on the under surface of the right lobe of the liver, running to the right of the hepatic hilum. It is easily visible in most (80%) of the cases where it remains open (partly or fully) and it usually contains right portal pedicle or its branches. During LC, it is best seen when the gallbladder neck is retracted towards the umbilical fissure. Clinical significance: The visible open sulcus acts as a fixed anatomical landmark during LC. It reliably indicates the plane of the CBD thus helps to reorient surgeon in cases of difficultly. All the dissection during the LC must be done ventral and cephalad to the line joining the roof of this sulcus and base of segment 4 (R4U line) as discussed later. During posterior dissection in the HC triangle, the dissection may be safely started by dividing the peritoneum immediately ventral and cephalad to the sulcus. Umbilical fissure This is a fissure between the left lateral section (segments 2, 3) and left medial section (segment 4) where the falciform ligament and ligamentum teres lie.

Clinical significance: This also acts as a fixed anatomical landmark, and helps the operating surgeon to reorient in difficult situations.

Segment 4

This is the left medial section of the liver. During LC it is identified easily by its location between the umbilical fissure and the gallbladder.

Clinical significance: The base of segment 4 acts as a fixed landmark. All the dissection in the HC triangle should be done cephalad to the R4U line. The initial assessment of size of this segment is important. This can be easily done by looking at the distance between the umbilical fissure and the gallbladder. Certain congenital conditions like segment 4 hypoplasia and ectopic gallbladder may need to be assessed correctly before the dissection begins to avoid inadvertent injury to bile duct.

Anatomical Variations

As the HC triangle is the primary surgical field during LC, it is important to know the clinically significant anatomic variations occurring in this area. These variations may pose challenges to the unfamiliar surgeon with a potential for BDI/VBI. Vascular anomalies: The cystic artery and the right hepatic artery (RHA) are two important vessels of concern during LC. The cystic artery is usually single (approximately 79%), originates from RHA, and most commonly (81.5%) traverses the HC triangle to supply the gallbladder throught its two branches – superficial and deep. However, this artery may have variations in its origin, number, or course. The most important of these variations includes: (1) the cystic artery passing anterior to the common hepatic/bile duct (17.9%); (2) a short (1 cm) cystic artery (9.5%); (3) multiple cystic arteries (8.9%); and (4) the cystic artery located inferior to the cystic duct (4.9%).

Clinical importance: If the presence of a short cystic artery is not appreciated during surgery, the right hepatic artery may be clipped and divided in a manner similar to that of the classic BDI. Keeping the dissection of the artery close to the gallbladder on the right side of the cystic lymph node (a fixed landmark) may prevent injury to the right hepatic artery. When the cystic artery arises from the gastroduodenal or left hepatic artery, it doesn’t pass through the HC triangle so can’t be localised during dissection in this triangle. When it arises from the gastroduodenal artery, the cystic artery passes inferior to the cystic duct (low lying cystic artery).

Anatomic variations of RHA are common. It usually passes behind the CHD (87%) before entering the HC triangle. An aberrant right hepatic artery (replaced or accessary) is also not uncommon. A replaced right hepatic artery, after coursing from behind the portal vein and CBD, comes to lie on the right side of the bile duct, and then travels close to the cystic duct and gallbladder and joins the right pedicle high up in the HC triangle.

Clinical importance: During dissection in the HC triangle, a replaced right hepatic artery may appear as a large cystic artery, and might be injured if not identified correctly. The right hepatic artery may take a tortuous course (Caterpillar turn/Moynihan’s hump) within the HC triangle, and it may lie very close to the gallbladder and the cystic duct before giving off a short cystic artery. Again, this aberrant course makes the right hepatic artery prone to injury during cholecystectomy.

Biliary ductal anomalies Important ductal anomalies relevant to LC involve variations in the cystic duct and right hepatic ductal system. The cystic duct is usually 2-4 cm long and 2-3 mm wide. It may be congenitally absent (very rare) or very long (5 cm or more). Usually it joins the CHD at an angle (angular insertion, 75%) but its course may be parallel (20%) or spiral (5%). It usually enters the CHD but there are variations: it may enter the right hepatic duct (0.6%-2.3%), anomalous right sectional duct, or CHD quite low near the ampulla. An anomalous right sectional duct, especially a right posterior sectional duct, may join the biliary tree at a level lower than usual. Rarely, there might be duplication of the CBD.

Clinical importance: The length and course of the cystic duct and its joining pattern with CHD are variable. However, its entire course and its junction with the CBD do not need to be delineated during LC as it is not required and it will put the bile duct at risk of injury specially in case of parallel insertion where the part of the cystic duct may be adherent to the CHD due to inflammation. A congenitally absent cystic duct is a very rare condition. If the cystic duct is not apparent during cholecystectomy then either it is short or it may be effaced by the stone or the Mirizzi syndrome is present.

The surgeon should be careful while dissecting in the HC triangle in such situation and may need to resort to one of the bail-out techniques as discussed later. Similarly, if two cystic ducts are visible, surgeon should be very careful in labelling this as double cystic ducts and dividing these structures. The anatomy should be clarified [e.g., with intraoperative cholangiography (IOC)] as these two ducts may be CBD and the CHD with a very short or effaced cystic duct, indicating that the dissection has gone behind the bile duct rather than through the HC triangle. The cystic duct diameter may be as much as 5 mm due to the passage of stone, and in this situation it may be confused with CBD. Inability to completely occlude the cystic duct with a medium-large clip should raise the suspicion of it to be CBD and this should be clarified (with proper display of CVS, and/or intraoperative imaging) before clipping and division. Anomalous low insertion of a right sectional duct (usually posterior), especially when the cystic duct joins it, will put this sectional duct at risk of injury if the surgeon is unaware of this variation and does not achieve CVS as discussed subsequently.

BE SAFE…

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