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Incidence, Patterns, and Clinical Relevance of Variant Portal Vein Anatomy

¹ All authors: Department of Diagnostic Radiology, Memorial Sloan Kettering Cancer Center, 1275 York Ave., New York, NY 10021.

Received January 12, 2004; accepted after revision April 19, 2004.

 
Address correspondence to A. M. Covey (coveya{at}mskcc.org).

Abstract

Top Abstract Introduction Materials and Methods Results Discussion References

 
OBJECTIVE. The purpose of this study was to determine the incidence of variant intrahepatic portal vein anatomy detected on CT portography and to discuss surgical implications.

CONCLUSION. Variant portal vein anatomy is nearly as common as variant hepatic artery anatomy. The complexity of hepatic interventions now performed by interventional radiologists and surgeons, including portal vein embolization, anatomic resection, and transplantation, make recognition and understanding of normal and variant portal vein anatomy increasingly important.

Introduction

Top Abstract Introduction Materials and Methods Results Discussion References

 
Knowledge of variant vascular anatomy can have critical implications during surgery and interventional radiology procedures [1–5]. Conventional catheter angiography, CT angiography, and MR angiography have proven invaluable in providing road maps of the visceral arterial supply before solid organ transplantation, visceral resection, arterial revascularization, and embolization [6–10].

In anticipation of liver surgery, CT or MRI is usually performed and can often define hepatic artery anatomy. Standard hepatic artery anatomy occurs in 50–75% of patients [1–3, 11]. Variant anatomy has important implications in planning liver resections or placement of hepatic artery infusion catheters or pumps [1–5]. Likewise, accurate assessment of arterial anatomy is increasingly important in planning percutaneous interventional hepatobiliary procedures, including hepatic artery embolization [4, 12].

The incidence of variant portal vein anatomy in the liver and the implications for surgical and radiologic interventions are increasingly apparent, particularly in the liver transplantation literature [13–15]. With the growing popularity of other complex hepatobiliary surgical and percutaneous procedures, including trisegmentectomy, portal vein embolization, and transjugular intrahepatic portosystemic shunts (TIPS), to name a few, the detection and recognition of portal vein variants are increasingly relevant.

The purpose of this study is to characterize and elucidate the incidence of various portal vein variants detected on CT portography in a cohort of preoperative patients.

Materials and Methods

Top Abstract Introduction Materials and Methods Results Discussion References

 
We retrospectively reviewed all CT portograms obtained at our institution between January 2000 and May 2001. Patients who had undergone previous liver resections and patients with large central tumors (defined as those that precluded accurate assessment of portal branch anatomy) were excluded from analysis. A waiver of authorization was obtained from the institutional review board for this study, and data were kept in a secure database that was registered in compliance with regulations of the Health Insurance Portability and Accountability Act.

During the 17-month study period, 216 CT portography procedures were performed at a single cancer center. Sixteen patients were excluded, including six who had undergone prior hepatic resection, three who had undergone prior portal vein embolization, and seven in whom large central tumors distorted the portal vein anatomy beyond interpretation. Therefore, a total of 200 patients were included in this study.

CT portography was performed by one of five board-certified interventional radiologists at a single center. Arterial access was most commonly via the right common femoral artery. A 4- or 5-French directional catheter was used to perform hepatic angiography, which included evaluation of the celiac axis and the superior mesenteric artery and checking for replaced or accessory vessels. The catheter was then placed in the superior mesenteric artery distal to the origin of any aberrant hepatic branches. With the catheter secured in position, the patient was transferred to a CT scanner (HiSpeed Advantage system, GE Healthcare) for conventional CT arterial portography, for which 170–190 mL of Omnipaque 140 (iohexol, Nycomed) was injected into the superior mesenteric artery catheter at a rate of 3 mL/sec. After a delay of 45–65 sec from the onset of the contrast injection, the liver was imaged in 7-mm helical slices. After a second delay of 20–30 sec, the scanning sequence was repeated.

Each 2D CT portogram was retrospectively and independently reviewed and classified into one of five categories (Figs. 1A, 1B, 1C, 1D, and 1E) by two of three interpreting interventional radiologists. Three-dimensional reconstructions were not performed for analysis of portal anatomy. If the two radiologists did not agree, the case was reviewed with the third radiologist and with the images obtained from conventional arterioportography. In this manner, consensus was achieved in all cases.

View larger version (26K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1A. —Illustrations show classification scheme of portal vein anatomy used in this study. LPV = left portal vein, RPPV = right posterior portal vein, RAPV = right anterior portal vein. (Printed with permission from Memorial Sloan-Kettering Cancer Center) Drawings depict standard portal vein anatomy (type 1, A), trifurcation (type 2, B), right posterior portal vein as first branch of main portal vein (type 3, C), segment VII branch as separate branch of right portal vein (types 4, D), and segment VI branch as separate branch of right portal vein (type 5, E).

View larger version (26K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1B. —Illustrations show classification scheme of portal vein anatomy used in this study. LPV = left portal vein, RPPV = right posterior portal vein, RAPV = right anterior portal vein. (Printed with permission from Memorial Sloan-Kettering Cancer Center) Drawings depict standard portal vein anatomy (type 1, A), trifurcation (type 2, B), right posterior portal vein as first branch of main portal vein (type 3, C), segment VII branch as separate branch of right portal vein (types 4, D), and segment VI branch as separate branch of right portal vein (type 5, E).

View larger version (34K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1C. —Illustrations show classification scheme of portal vein anatomy used in this study. LPV = left portal vein, RPPV = right posterior portal vein, RAPV = right anterior portal vein. (Printed with permission from Memorial Sloan-Kettering Cancer Center) Drawings depict standard portal vein anatomy (type 1, A), trifurcation (type 2, B), right posterior portal vein as first branch of main portal vein (type 3, C), segment VII branch as separate branch of right portal vein (types 4, D), and segment VI branch as separate branch of right portal vein (type 5, E).

View larger version (31K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1D. —Illustrations show classification scheme of portal vein anatomy used in this study. LPV = left portal vein, RPPV = right posterior portal vein, RAPV = right anterior portal vein. (Printed with permission from Memorial Sloan-Kettering Cancer Center) Drawings depict standard portal vein anatomy (type 1, A), trifurcation (type 2, B), right posterior portal vein as first branch of main portal vein (type 3, C), segment VII branch as separate branch of right portal vein (types 4, D), and segment VI branch as separate branch of right portal vein (type 5, E).

View larger version (33K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1E. —Illustrations show classification scheme of portal vein anatomy used in this study. LPV = left portal vein, RPPV = right posterior portal vein, RAPV = right anterior portal vein. (Printed with permission from Memorial Sloan-Kettering Cancer Center) Drawings depict standard portal vein anatomy (type 1, A), trifurcation (type 2, B), right posterior portal vein as first branch of main portal vein (type 3, C), segment VII branch as separate branch of right portal vein (types 4, D), and segment VI branch as separate branch of right portal vein (type 5, E).

Results

Top Abstract Introduction Materials and Methods Results Discussion References

 
Two hundred sixteen consecutive patients underwent hepatic angiography and CT portography during the study period. Six patients were excluded on the basis of prior hepatic resection, and seven patients were excluded because of large central tumors precluding filling and interpretation of portal vein branch anatomy. Three patients had previously undergone portal vein embolization and were also excluded from this study. Therefore, a total of 200 CT portograms were available for interpretation. Our results are summarized in Table 1.

One hundred thirty patients had type 1 anatomy (Figs. 1A, 1B, 1C, 1D, and 1E), or standard portal vein anatomy, in which the main portal vein divides into the right and left portal branches. The right portal vein then gives rise to anterior and posterior sectorial branches that supply Couinaud liver segments V and VIII and segments VI and VII, respectively (Figs. 2A, 2B, 2C, and 2D).

View larger version (114K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2A. —45-year-old man with metastatic colorectal cancer. CT portograms show standard portal vein anatomy. Main portal vein divides into left portal vein (arrow, A) and right portal vein, which subsequently divides into right anterior portal vein (arrow, C) to supply segments V and VIII, and right posterior portal vein (arrow, D) to supply segments VI and VII. It is uncommon for all major branches to be seen on a single image, and being able to scroll through images on workstation or PACS is invaluable in correctly identifying and classifying variant anatomy. Multiplanar reconstruction may also overcome this limitation of 2D imaging.

View larger version (117K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2B. —45-year-old man with metastatic colorectal cancer. CT portograms show standard portal vein anatomy. Main portal vein divides into left portal vein (arrow, A) and right portal vein, which subsequently divides into right anterior portal vein (arrow, C) to supply segments V and VIII, and right posterior portal vein (arrow, D) to supply segments VI and VII. It is uncommon for all major branches to be seen on a single image, and being able to scroll through images on workstation or PACS is invaluable in correctly identifying and classifying variant anatomy. Multiplanar reconstruction may also overcome this limitation of 2D imaging.

View larger version (112K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2C. —45-year-old man with metastatic colorectal cancer. CT portograms show standard portal vein anatomy. Main portal vein divides into left portal vein (arrow, A) and right portal vein, which subsequently divides into right anterior portal vein (arrow, C) to supply segments V and VIII, and right posterior portal vein (arrow, D) to supply segments VI and VII. It is uncommon for all major branches to be seen on a single image, and being able to scroll through images on workstation or PACS is invaluable in correctly identifying and classifying variant anatomy. Multiplanar reconstruction may also overcome this limitation of 2D imaging.

View larger version (116K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2D. —45-year-old man with metastatic colorectal cancer. CT portograms show standard portal vein anatomy. Main portal vein divides into left portal vein (arrow, A) and right portal vein, which subsequently divides into right anterior portal vein (arrow, C) to supply segments V and VIII, and right posterior portal vein (arrow, D) to supply segments VI and VII. It is uncommon for all major branches to be seen on a single image, and being able to scroll through images on workstation or PACS is invaluable in correctly identifying and classifying variant anatomy. Multiplanar reconstruction may also overcome this limitation of 2D imaging.

Variations from standard portal vein anatomy were seen in the remaining 70 patients. Trifurcation (type 2 anatomy) of the main portal vein into the right anterior, right posterior, and left portal vein branches occurred in 18 patients (Figs. 3A, 3B, and 3C). The most common variant was the so-called Z type of anatomy (type 3), seen in 26 patients, in which the right posterior portal vein is the first branch of the main portal vein and the left portal vein is the terminal branch, arising after the origin of the right anterior portal vein (Figs. 4A, 4B, 4C, and 4D). In 14 patients, the segment VI or segment VII branch was the first branch of the right portal vein (types 5 and 4 anatomy, respectively), as seen in Figures 5A, 5B, 5C, 5D, 5E, 5F, and 5G.

View larger version (110K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3A. —CT portograms in 54-year-old woman with portal vein trifurcation (type 2 anatomy) and metastatic colorectal cancer. In 9% of patients, main portal vein trifurcates into left portal vein (straight thin arrow), right anterior portal vein (straight thick arrow), and right posterior portal vein (curved arrow), as depicted in single 2D image in this patient.

View larger version (116K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3B. —CT portograms in 54-year-old woman with portal vein trifurcation (type 2 anatomy) and metastatic colorectal cancer. More typically, trifurcation is less apparent and requires scrolling through images with attention to portal vein to accurately determine anatomy. In C, straight arrow indicates right anterior portal vein, curved arrow indicates right posterior branch.

View larger version (119K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3C. —CT portograms in 54-year-old woman with portal vein trifurcation (type 2 anatomy) and metastatic colorectal cancer. More typically, trifurcation is less apparent and requires scrolling through images with attention to portal vein to accurately determine anatomy. In C, straight arrow indicates right anterior portal vein, curved arrow indicates right posterior branch.

View larger version (104K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4A. —CT portograms in 47-year-old man with metastatic colorectal cancer shows Z type of portal vein variant (type 3 anatomy). In this patient, right posterior portal vein (arrow, A) is first branch of main portal vein. Common trunk of variable length gives rise to left portal vein (arrow, B) and right anterior portal vein (arrow, C).

View larger version (108K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4B. —CT portograms in 47-year-old man with metastatic colorectal cancer shows Z type of portal vein variant (type 3 anatomy). In this patient, right posterior portal vein (arrow, A) is first branch of main portal vein. Common trunk of variable length gives rise to left portal vein (arrow, B) and right anterior portal vein (arrow, C).

View larger version (117K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4C. —CT portograms in 47-year-old man with metastatic colorectal cancer shows Z type of portal vein variant (type 3 anatomy). In this patient, right posterior portal vein (arrow, A) is first branch of main portal vein. Common trunk of variable length gives rise to left portal vein (arrow, B) and right anterior portal vein (arrow, C).

View larger version (119K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4D. —CT portograms in 47-year-old man with metastatic colorectal cancer shows Z type of portal vein variant (type 3 anatomy). In this patient, right posterior portal vein (arrow, A) is first branch of main portal vein. Common trunk of variable length gives rise to left portal vein (arrow, B) and right anterior portal vein (arrow, C).

View larger version (107K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5A. —CT portograms in 58-year-old man with metastatic colorectal cancer. CT portograms show liver segment VI portal branch (star, A) arising as first branch of main portal vein. Segment VII branch (arrow, B) arises from right anterior portal vein (arrow, C).

View larger version (103K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5B. —CT portograms in 58-year-old man with metastatic colorectal cancer. CT portograms show liver segment VI portal branch (star, A) arising as first branch of main portal vein. Segment VII branch (arrow, B) arises from right anterior portal vein (arrow, C).

View larger version (111K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5C. —CT portograms in 58-year-old man with metastatic colorectal cancer. CT portograms show liver segment VI portal branch (star, A) arising as first branch of main portal vein. Segment VII branch (arrow, B) arises from right anterior portal vein (arrow, C).

View larger version (114K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5D. —CT portograms in 58-year-old man with metastatic colorectal cancer. CT portograms show liver segment VI portal branch (star, A) arising as first branch of main portal vein. Segment VII branch (arrow, B) arises from right anterior portal vein (arrow, C).

View larger version (111K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5E. —CT portograms in 58-year-old man with metastatic colorectal cancer. CT portograms show liver segment VI portal branch (star, A) arising as first branch of main portal vein. Segment VII branch (arrow, B) arises from right anterior portal vein (arrow, C).

View larger version (111K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5F. —CT portograms in 58-year-old man with metastatic colorectal cancer. CT portograms show liver segment VI portal branch (star, A) arising as first branch of main portal vein. Segment VII branch (arrow, B) arises from right anterior portal vein (arrow, C).

View larger version (111K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5G. —CT portograms in 58-year-old man with metastatic colorectal cancer. Transhepatic portal venogram (obtained on another date) confirms interpretation of variant portal anatomy. Arrow represents left portal vein, star indicates segment VI branch.

Twelve patients had other portal vein variants. Half of these had trifurcation of the right portal vein into the right anterior sectorial portal trunk and into segment VI and segment VII branches (Figs. 6A, 6B, 6C, and 6D). One patient each had the following anomalies: division of the main portal vein into segment VI, segment VII, right anterior portal vein, and left portal vein as a "quadrifurcation"; trifurcation of the right portal vein into branches supplying segment V, segment VIII, and the right posterior sectorial trunk; segments IV and VII branches originating from the right anterior portal vein; an accessory segment VI branch from the right portal vein in a patient with type 5 portal vein branching; and one patient with trifurcation of the main portal vein into segment VI branch, left and right anterior sectorial branches, and segment VII branch (Figs. 7A, 7B, 7C, 7D, 7E, and 7F).

View larger version (104K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6A. —51-year-old man with metastatic colorectal cancer. CT portograms show right portal vein trifurcates into right anterior portal vein (arrow, B) and segment VI (curved arrow, C) and segment VII (straight arrow, C) branches. Left portal vein is denoted by arrow in A. This anatomy is surgically relevant to left trisegmentectomy, in which damage to either right posterior segment branch would leave patient with single-segment remnant liver.

View larger version (105K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6B. —51-year-old man with metastatic colorectal cancer. CT portograms show right portal vein trifurcates into right anterior portal vein (arrow, B) and segment VI (curved arrow, C) and segment VII (straight arrow, C) branches. Left portal vein is denoted by arrow in A. This anatomy is surgically relevant to left trisegmentectomy, in which damage to either right posterior segment branch would leave patient with single-segment remnant liver.

View larger version (101K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6C. —51-year-old man with metastatic colorectal cancer. CT portograms show right portal vein trifurcates into right anterior portal vein (arrow, B) and segment VI (curved arrow, C) and segment VII (straight arrow, C) branches. Left portal vein is denoted by arrow in A. This anatomy is surgically relevant to left trisegmentectomy, in which damage to either right posterior segment branch would leave patient with single-segment remnant liver.

View larger version (100K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6D. —51-year-old man with metastatic colorectal cancer. CT portograms show right portal vein trifurcates into right anterior portal vein (arrow, B) and segment VI (curved arrow, C) and segment VII (straight arrow, C) branches. Left portal vein is denoted by arrow in A. This anatomy is surgically relevant to left trisegmentectomy, in which damage to either right posterior segment branch would leave patient with single-segment remnant liver.

View larger version (126K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7A. —59-year-old man with metastatic colorectal cancer. CT portograms show single patient in our series in whom portal vein variant branch pattern involved left portal vein. In this patient, segment IV portal vein (arrow, F) arose from right portal vein (straight arrow, E) and not from left portal vein, which supplied only lateral segment. Curved arrow (E) indicates segment VI portal vein branch. If it is not recognized before procedure in a patient undergoing portal vein embolization, segment IV branch could be inadvertently embolized during right portal vein embolization or inadvertently not embolized during left portal vein embolization.

View larger version (127K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7B. —59-year-old man with metastatic colorectal cancer. CT portograms show single patient in our series in whom portal vein variant branch pattern involved left portal vein. In this patient, segment IV portal vein (arrow, F) arose from right portal vein (straight arrow, E) and not from left portal vein, which supplied only lateral segment. Curved arrow (E) indicates segment VI portal vein branch. If it is not recognized before procedure in a patient undergoing portal vein embolization, segment IV branch could be inadvertently embolized during right portal vein embolization or inadvertently not embolized during left portal vein embolization.

View larger version (125K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7C. —59-year-old man with metastatic colorectal cancer. CT portograms show single patient in our series in whom portal vein variant branch pattern involved left portal vein. In this patient, segment IV portal vein (arrow, F) arose from right portal vein (straight arrow, E) and not from left portal vein, which supplied only lateral segment. Curved arrow (E) indicates segment VI portal vein branch. If it is not recognized before procedure in a patient undergoing portal vein embolization, segment IV branch could be inadvertently embolized during right portal vein embolization or inadvertently not embolized during left portal vein embolization.

View larger version (126K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7D. —59-year-old man with metastatic colorectal cancer. CT portograms show single patient in our series in whom portal vein variant branch pattern involved left portal vein. In this patient, segment IV portal vein (arrow, F) arose from right portal vein (straight arrow, E) and not from left portal vein, which supplied only lateral segment. Curved arrow (E) indicates segment VI portal vein branch. If it is not recognized before procedure in a patient undergoing portal vein embolization, segment IV branch could be inadvertently embolized during right portal vein embolization or inadvertently not embolized during left portal vein embolization.

View larger version (132K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7E. —59-year-old man with metastatic colorectal cancer. CT portograms show single patient in our series in whom portal vein variant branch pattern involved left portal vein. In this patient, segment IV portal vein (arrow, F) arose from right portal vein (straight arrow, E) and not from left portal vein, which supplied only lateral segment. Curved arrow (E) indicates segment VI portal vein branch. If it is not recognized before procedure in a patient undergoing portal vein embolization, segment IV branch could be inadvertently embolized during right portal vein embolization or inadvertently not embolized during left portal vein embolization.

View larger version (131K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7F. —59-year-old man with metastatic colorectal cancer. CT portograms show single patient in our series in whom portal vein variant branch pattern involved left portal vein. In this patient, segment IV portal vein (arrow, F) arose from right portal vein (straight arrow, E) and not from left portal vein, which supplied only lateral segment. Curved arrow (E) indicates segment VI portal vein branch. If it is not recognized before procedure in a patient undergoing portal vein embolization, segment IV branch could be inadvertently embolized during right portal vein embolization or inadvertently not embolized during left portal vein embolization.

Discussion

Top Abstract Introduction Materials and Methods Results Discussion References

 
As the complexity of liver interventions by both surgeons and radiologists expands, increasing awareness of standard and variant anatomy is critical. This complexity has been well documented in the liver transplantation literature, and many surgeons routinely obtain preoperative CT or MR angiograms to check for replaced or accessory arterial and venous branches [1–4, 14–16]. With the increase in percutaneous hepatobiliary interventions and complex surgical resections, a thorough understanding of variants in portal vein anatomy is crucial. In most cases, preprocedure cross-sectional imaging is available, and although portal vein variants are depicted on the images, they are not commonly reported. In this study, we assessed portal vein anatomy using CT portography to determine the incidence and patterns of variants in patients who were scheduled for liver surgery.

In standard portal vein anatomy, the splenic and superior mesenteric veins join to form the main portal vein posterior to the head of the pancreas. The main portal vein, which carries as much as 80% of the blood supply to the liver, typically divides at the hilus into the left and larger right portal branches. The left portal vein courses medially to the umbilical fissure and supplies segments II, III, and IV and a caudate branch. The right portal vein divides into the right anterior sector trunk, which in turn divides into segment V and segment VIII branches, and the right posterior sector trunk, which supplies segments VI and VII [17].

Embryologically, the portal vein is formed in the second month of gestation by selective involution of the vitelline veins, which have multiple bridging anastomoses anterior and posterior to the duodenum. Alterations in the pattern of obliteration of these anastomoses can result in several variants [18].

Several dramatic portal vein variants have been described [19–21], including duplications, congenital absence, and absence of portal vein branching (in which a single portal vein enters the right liver and courses into the left, giving only segmental branches along its course). These variants can be quite obvious with modern cross-sectional imaging.

Far more common in our experience, however, are more subtle variants that may easily be overlooked but can have important clinical consequences. For example, if the segment VI or VII portal vein arises alone as the first branch of the main portal vein, a left trisegmentectomy may inadvertently leave a single viable liver segment as the entire remnant liver, potentially resulting in liver failure and death. Failure to recognize a Z type portal vein variant (type 3) during a left liver resection or when harvesting a living donor liver transplant may result in loss of perfusion to the right anterior sector and compromise the remnant liver. Trifurcation of the portal vein may require two separate anastomoses when the right liver is transplanted to an adult donor [22].

We retrospectively reviewed 200 patients who underwent preoperative hepatic angiography and CT portography, with attention to portal vein anatomy. We chose this group of patients because doing so provided us two opportunities to determine portal vein anatomy: conventional arterioportography and CT portography. Additionally, because these patients underwent CT portography for the sole purpose of operative planning, each was scheduled to undergo hepatic surgery, which made the anatomy particularly relevant in these patients.

In this study, 35% of patients had variant portal vein anatomy, which is significantly greater than the 10–15% described in early published data from the sonography literature [23, 24] that is still widely quoted. In our cohort, 22% patients had either trifurcation (type 2) or Z (type 3) anatomy. Fourteen patients (7%) had what we considered a single posterior segment branch (types 4 and 5) arising as the first branch of the right portal vein. Identifying these variants in patients who are to undergo left trisegmentectomy can alert the surgeon and avoid a potentially life-threatening complication.

In our series, variants of the left portal vein were rare. In only one patient (Figs. 7A, 7B, 7C, 7D, 7E, and 7F) did the segment IV portal vein arise anomalously from the right anterior portal vein. None of the 200 patients in this study had congenital duplication or absence of the portal vein.

Our findings are consistent with those of Cheng et al. [13], who found 65% of 200 patients who underwent conventional arterioportography had standard portal vein anatomy. Their study was limited, however, because conventional arterioportography is limited in determining segmental branch patterns; in fact, those authors were able to classify the anatomy of only the main, left, right anterior, and right posterior portal veins. With the excellent detail provided by CT angiography and MR angiography, conventional arterioportography is not widely used in this country for delineation of anatomy in this patient population.

Cheng et al. [25] published a larger series of 688 potential donors patients evaluated for living related liver transplantation. In that series, 7% of patients were determined to be unsuitable candidates or to potentially require a more technically challenging surgery such as a venous graft because of variant portal vein anatomy. Again, only conventional arterioportography was used, so they may have missed some uncommon but relevant anomalies.

In a more recent study of 24 patients who underwent pretransplantation MR angiography to delineate hepatic vasculature, conventional portal vein anatomy was detected in 76% [26]. Four patients (16%) had trifurcation and an additional two (8%) had Z type anatomy (type 3) [26]. That study did not identify cases in which the first branch of the right portal vein was a single segment (segment VI or VII) portal vein branch, which occurred in 7% of our cases; nor were other variants identified, as were seen in 6% of patients in our series.

Knowledge of portal vein variants is also increasingly important in percutaneous interventional procedures. Transhepatic portal vein embolization is gaining acceptance as a method to induce contralateral liver hypertrophy in patients with small future remnant livers [27]. To perform embolization safely and efficaciously, the interventional radiologist must have an understanding of variant anatomy. Embolizing a nontargeted sector or segment in this patient population can make potentially resectable anatomy unresectable.

TIPS is another interventional procedure in which portal vein anatomy may be relevant. TIPS placement often depends on the blind canalization of the portal vein by a puncture originating from the hepatic vein. In standard anatomy, the portal vein lies in a predictable position relative to the hepatic vein, accounting for high success rates. Although typically hepatic vein anatomy is most important in performing TIPS, success can also depend on portal vein anatomy. For example, in portal vein trifurcatrion the portal vein puncture site created during a TIPS placement can be acute and therefore difficult to stent. In other cases, variant portal vein anatomy may preclude successful access using a standard approach. Some authors have advocated using cross-sectional imaging before or during the TIPS procedure to assess the venous anatomy for preprocedure planning [20, 28].

One potential limitation of our study is that we did not use 3D reconstruction to confirm our interpretation of portal vein anatomy. We chose to study this patient population because of the excellent delineation of the portal vein and its branches on CT portography, as well as the ability to compare the cross-sectional images with conventional arterial portograms in patients in whom categorization of the portal vein anatomy using CT alone was difficult. Because ours is a retrospective study, the images were not acquired with the intention of 3D reconstruction, and the raw data were not available. Although multiplanar reconstruction with either CT angiography or MR angiography might make portal vein variants easier to recognize, to date these techniques are not routinely performed on every patient in anticipation of hepatobiliary surgery or intervention, and therefore they are not as generally applicable as routine 2D CT.

In conclusion, variant portal vein anatomy is more common than previously reported in the sonography literature and is increasingly relevant to the practice of safe and efficacious surgical and percutaneous hepatobiliary intervention. In this group of patients, the portal vein is almost always depicted on preoperative cross-sectional imaging, and critical attention to portal vein anatomy may prevent significant complications.

References

Top Abstract Introduction Materials and Methods Results Discussion References

 

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