I previously wrote a blog around rotation of the porta hepatis and the conformational changes that this can cause. Changes in the volume of relative components of the liver can also cause changes in the main portal venous trunk. This can alter the conformation of the portal vein and can cause difficulties in either understanding the anatomy or potential complications during liver or biliary surgery. The major effects on portal vein anatomy come from atrophy of the right liver. Changes in the left liver do not really impact on angularity of the portal venous confluence.
There are a number of well described anatomical variants of the portal venous anatomy which you can read about in these articles.
Portal vein normal anatomy and variants: implication for liver surgery and portal veinembolization. Schmidt S, Demartines N, Soler L, Schnyder P, Denys A. Semin Intervent Radiol. 2008 Jun;25(2):86-91.
Reappraisal of right portal segmental ramification based on 3-dimensional volume rendering of computed tomography during arterial portography. Wu TC, Lee RC, Chau GY, Chiang JH, Chang CY.J Comput Assist Tomogr. 2007 May-Jun;31(3):475-80.
Anatomical variations and surgical strategies in right lobe living donor liver transplantation: lessons from 120 cases. Nakamura T, Tanaka K, Kiuchi T, Kasahara M, Oike F, Ueda M, Kaihara S, Egawa H, Ozden I, Kobayashi N, Uemoto S. Transplantation. 2002 Jun 27;73(12):1896-903.
The most common variant has the main portal vein dividing into a right and left main portal vein the right subsequently divides into right anterior sectoral and right posterior sectoral branches. (This variant occurs in more than 90% of patients).
So being just a simple surgeon I am all for making things as easy as possible. So we can look at the main bifurcation as the letter Y. Now it is possible to look at what happens to this Y shaped bifurcation in a number of clinical settings.Atrophy of the Right lobe
There are lots of different situations which can give rise to atrophy of the right lobe common causes are cholangiocarcinoma of the right duct, cirrhosis, primary sclerosing cholangitis, hepatic abscess (chronic), right portal vein thrombosis secondary to sepsis, chronic intrahepatic cholelithiasis and cholangitis.
When there is atrophy of the right lobe of liver the effect is to pull on the right portal vein and flatten the normal Y configuration. So the Y becomes a ‘T’. This can also occur with a large space occupying lesion in segment 4/5 which pushes the portal veins apart. As atrophy and therefore traction increases the distortion of the portal confluence increases.This distortion is important in surgery because if the patient is planned to have a right hepatic resection it becomes very important to resect the right portal vein at a point where it is not likely to compromise the left portal vein. In the example below, transection at line A will cause severe compromise of the left portal vein and jeopardise the future liver remnant. Transection at line B is much safer and will preserve flow to the left portal vein. This change in angulation is sometimes difficult to appreciate but should be anticipated where there is significant right lobar atrophy.Previous extended right hepatectomy/ right trisectionectomy
When the right hepatic segments and segment 4 are removed the remaining portal vein becomes very redundant and the angle between the main portal vein and left portal vein becomes very acute. This looks to me like a backwards number ‘7’.The left portal vein is usually quite long and removal of segment 4 creates this long angle. This is the basis for portal vein resection and reconstruction in cholangiocarcinoma popularised by Peter Neuhaus from Berlin. This technique involves resection of the hilar lesion together with the left hepatic duct and confluence of the portal veins and uses the fact that the left vein is so long to permit reconstruction without need for use of an interposition graft (usually!). Oncological superiority of hilar en bloc resection for the treatment of hilar cholangiocarcinoma. Neuhaus P, Thelen A, Jonas S, Puhl G, Denecke T, Veltzke-Schlieker W, Seehofer D.Ann Surg Oncol. 2012 May;19(5):1602-8.
Extended resections for hilar cholangiocarcinoma. Neuhaus P, Jonas S, Bechstein WO, Lohmann R, Radke C, Kling N, Wex C, Lobeck H, Hintze R. Ann Surg. 1999 Dec;230(6):808-18; discussion 819.
Anticipating the potential effects of the disease process on the vascular anatomy is important to avoid potentially disastrous errors in understanding the anatomy resulting in either bleeding or compromise of the future liver remnant. Whenever there is a major change in the liver either a large space occupying lesion or atrophy of part of the liver, it is worth considering what the likely impact is on the vascular anatomy.
While this blog may sound a bit like an episode of Sesame Street, I personally think it is useful to know about the Y, the T and the backward 7 of portal veins!