Posterior Superior Pancreaticoduodenal Vein

1033

Posterior Superior Pancreaticoduodenal Mimic of Distal at Sonography

Ronald

Vein:

Common

Bile Duct

OBJECTIVE. Previous investigators have noted that the common bile duct may appear to merge with the portal vein on sagittal sonograms, mimicking a venous structure. The posterior superior pancreaticoduodenal vein courses adjacent to the distal part of the common bile duct within the pancreatic head. A prospective study was performed to assess the sonographic appearance of the posterior superior pancreaticoduodenal vein. SUBJECTS AND METHODS. The study included 50 consecutive subjects in whom the pancreatic head was well seen. Anatomic characteristics of the posterior superior pancreaticoduodenal vein were noted with gray-scale, duplex Doppler, and color Doppler sonography. The site of insertion of the posterior superior pancreaticoduodenal vein into the portal vein was noted. RESULTS. The posterior superior pancreaticoduodenal vein was visualized in all 50 cases. Although it usually (82% of cases) inserted into the posterior aspect of the portal vein, the posterior superior pancreaticoduodenal vein inserted into the anterior aspect of the portal vein in nine cases (18%), resulting in an appearance mimicking the common bile duct on sagittal sonograms. Doppler examination showed flow toward the portal vein in all obliquely oriented posterior superior pancreaticoduodenal veins, and in 40% overall. The common bile duct could always be followed into the ports hepatis and was anterior to the posterior superior pancreaticoduodenal vein in 49 cases (98%). CONCLUSION. The posterior superior pancreaticoduodenal vein can be seen routinely on sonograms when the pancreatic head is unobscured, and it can mimic the common bile duct in a significant number of cases. These structures can be distinguished by noting continuation of the common bile duct into the porta hepatis, the generally anterior position of the common bile duct, and flow in the posterior supe-

H. Wachsberg1

nor

pancreaticoduodenal

vein

on

Doppler

examination.

Awareness

and anatomy of the posterior superior pancreaticoduodenal sion with the common bile duct at sonographic examination. AJR

Received September 15, 1992; revision December 18, 1992.

Presented

accepted

after

at the annual meeting of the Society

of Gastrointestinal January 1993. 1 Department

Radiologists, of Radiology,

Scottsdale, University

and University of Medicine soy-New Jersey Medical

AZ,

Hospital

& Dentistry of Now JonSchool, 150 Bergen St., Room C-320, Newark, NJ 07103. Address comespondence to R. H. Wachsberg.

0361-803X/93/1605-1033 © American Roentgen

Ray Society

1993;160:1

of the

vein minimizes

existence

its confu-

033-1037

The common bile duct exits the liven anterior to the portal vein, then courses postenoinfeniorly in an oblique fashion through the pancreatic head toward the papilla of Vaten [1]. The distal intrapancreatic portion of the common bile duct should be visualized, even in the absence of biliary dilatation, as it may be of nonmal caliber in up to 33% of patients with chobedocholithiasis [2]. As the duct crosses the portal vein, it may artifactualby appear to join the vein’s antenoinfenior margin in a single sagittal projection (Fig. 1). This phenomenon has been noted as a potential pitfall during sonographic examination [3]. During abdominal sonographic examinations at this institution, two tubular structures have increasingly been noted to course obliquely through the pancreatic head, often adjacent to one another. Only one of these (the common bile duct) continues into the porta hepatis, whereas the other does indeed join the portal vein. Evaluation of the latter structure with Doppler imaging reveals venous flow toward the portal vein. A vessel with this anatomic configuration is the poste-

WACHSBERG

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AJR:160,

May 1993

Fig. 1 .-Sagittal sonogram shows common bile duct (arrowhead) appearing to join portal vein. Imaging in other planes confirmed that this structure was common bile duct. C = inferior vena cava, P = portal vein.

Fig. 2.-Anatomic illustration depicting posterior superior pancreaticoduodenal vein lying posteromedial to common bile duct as the former ascends to drain Into portal vein. Common bile duct and adjacent posterior superior pancreaticoduodenal vein often follow a similar oblique course in this region.

1

2

non superior pancreaticoduodenab vein (PSPDV), which is present in virtually all persons [4, 5] (Fig. 2). The PSPDV has been noted on CT scans [6, 7] and MR images [6]. Although unspecified pancreaticoduodenal vascuban structures have been noted in passing at sonographic examination [8], I know of no reports of the sonognaphic appearance of the PSPDV. A prospective study was penformed to assess the sonographic appearance of the PSPDV and to determine guidelines for distinguishing it from the common bile duct.

Subjects

and

was sought

in consecutive

prospectively

subjects

in whom

at sonographic the

distal

common

bile

were

excluded

if either

of these

structures

could

gist

with

physicians.

Acuson

to 5.0-MHz

128

Examinations XP-10

convex-array

(Mountain

sector

transducers.

and

The PSPDV was identified inferolateral

aspect

superiorly

were

the

portal

evaluations

performed

vein.

head,

not

be

at instrument

CA)

and

originating

coursing Doppler

and colon Doppler

settings

optimized

inferior

vena

cava

was

assumed

in the

medially

and

angle

was

slow

to the

coronal

plane in all cases. On a sagittal sonogram that included the inferior vena cava, PSPDV insertion into the portal vein was recorded. A line

bisecting

the

portal

vein

along

its midcoronal

plane

was

drawn

parallel to the inferior vena cava (Fig. 3). Anastomosis of the PSPDV with the portal vein anterior to this line was termed anterior insertion,

whereas

posterior

insertion.

The relationship noted. If the cystic sis of the PSPDV

anastomosis

posterior

of the PSPDV

to this

to the common

line

was

labeled

bile duct was

duct joined the bile duct caudal to the anastomowith the portal vein, or a replaced right hepatic

artery traversed the portacaval space, PSPDV to these structures was noted.

of a right

paramedian sagittal image through revena cava posteriorly. Broken line through inferior vena cava indicates coronal plane. A parallel broken line bisects portal vein, which is Imaged en face. Anastomosis of posterior superior pancreaticoduodenal vein with portal vein anterior to this line Is termed anterior insertion (vein A). Anastomosis posterior to this line is termed posterior insertion (vein P).

head with inferior

mum anterior

luminal

diameter

antenopostenior and

PSPDV was measured

of the distance

posterior

venous

between walls

the

in the

inner

sagittal

as the maxi-

surfaces

of

the

plane.

techniques

to show

to lie parallel

drawing

2.5-

venous flow. Imaging was performed in transverse and sagittal planes as well as at various degrees of obliquity, depending on the course of the PSPDV. The

Fig. 3.-Line

gion of pancreatic

The

If a suitable

with pulsed

\-.-,_.f

by a radiobo-

View,

as a tubular structure

of the pancreatic

to join

obtainable,

were performed

systems

-

duct

seen. Those with clinical or imaging findings suggestive of liver on pancreatic disease also were excluded. Fifty subjects 1 6-55 years old were included in the study group. The first six subjects were volunteers. In the remaining 44 cases, sonograms had been requested

by referring

U)-

VenaCava

examina-

was well visualized along its entire course through the pancreatic head and the proximal gastroduodenal artery could be seen as well. Subjects

Inferior

Methods

The PSPDV tion

ii

the relationship

of the

Results

The PSPDV distinct from the common bile duct was imaged in all 50 subjects in whom both the common bile duct and gastroduodenab artery were seen, as required for inclusion in the study. In these cases, a tubular structure in the expected location of the PSPDV anastomosing with the pontab vein was always visualized, distinct from the common bile duct, which always could be followed to the porta hepatis. In 20 cases (40%), pulsed Doppler (Fig. 4) and/on color DoppIer (Fig. 5) imaging showed flow toward the portal vein. In the remaining 30 cases (60%), flow evaluation was limited by difficulty in obtaining a suitable Doppler angle as the PSPDV approached the coronal plane; by the subject’s inability

to suspend

sations

from

the

respiration

adjacent

adequately;

great

vessels,

on by intense

which

pub-

in some

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May 1993

SUPERIOR

PANCREATICODUODENAL

cases caused the adjacent PSPDV to be in motion throughout the cardiac cycle. In 41 cases (82%), the PSPDV inserted on the posterior aspect of the portal vein (Fig. 6). Anterior insertion of the PSPDV into the portal vein occurred in the other nine cases (18%, Fig. 7). In each instance of anterior PSPDV insertion, flow

was

demonstrated

with

Doppler

techniques.

In 49 cases

(98%), the common bile duct was anterior to the PSPDV (Fig. 8). In one case (2%), the reverse was noted (Fig. 9). The diameter of the PSPDV was 1 .9 ± 0.9 mm (mean ± SD; range, 1 .0-4.5 mm). The cystic duct extended caudal to the junction of the PSPDV and the portal vein in five cases (10%). In four of these,

the

cystic

duct

coursed

between

the

PSPDV

and

the

common hepatic duct before inserting into the posterior aspect of the common hepatic duct. In one case, the cystic duct was posterior to both the PSPDV and the common hepatic duct. A replaced right hepatic artery was noted in four cases (8%) and was posterior to the PSPDV in three of these, but could always be traced to the superior mesentenic artery and never simulated the course of the PSPDV (Fig. 9). In one case (2%), the PSPDV originated in the antenoinfenion pancreas, coursing posterosupenionly in oblique fashion toward the portal vein. Duplication of the PSPDV was noted once (2%).

Fig. 4.-Pulsed tenor superior shows

venous

Doppler sonogram pancreaticoduodenal flow toward

portal

of posvein

vein.

Fig. 5.-Sagittal color Doppler sonogram shows flow toward portal vein (P) within postenor superior pancreaticoduodenal vein (solid black arrows). Note similarity of postenor superior pancreaticoduodenal vein to common bile duct illustrated in Fig. 1 . Portions of gastroduodenal artery (open arrow) and common bile duct (white arrow) are seen. h = hepatic artery, C = inferior vena cava, R = right renal artery.

Fig. 6.-Sagittal sonogram shows posterior insertion of posterior superior pancreaticoduodenal vein (black arrow) into portal vein (P). Common bile duct (white arrow) Is anterior to posterior superior pancreaticoduodenal vein. C = Inferior vena cava.

Fig. 7.-Sagittal sonogram shows anterior insertion of posterior superior pancreaticoduodenal vein (arrow) into portal vein (P). C = inferior vena cava.

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Discussion

The PSPDV is the major draining vein of the posterior pancreatic head and adjacent duodenum. It usually joins the portal vein just superior to the pancreas, alternatively anastomosing at or inferior to the level of the pancreatic neck in 38% of cases [4, 5]. Caudal to its anastomosis with the pontab vein, the PSPDV usually lies posterior to the common bile duct, often following a parallel oblique course through the pancreatic head [9-11]. It is the only pancneaticoduodenal vein that typically inserts directly into the portal vein. Failure to appreciate the presence and proximity of the PSPDV can result in its misidentification as the common bile duct, leading to the impression that distal ductab abnormality (e.g., cabcubus) has been excluded. Conversely, the common bile duct may artifactually appear to merge with the portal vein, mimicking a venous structure [3]. In this study, the PSPDV was identified at sonognaphy in 50 consecutive persons in whom the pancreatic head was well visualized; it was posterior to the common bile duct in 49 (98%) of these cases. Therefore, sonognaphic identification of two adjacent, obliquely oriented tubular structures within the pancreatic head usually indicates that the common bile duct is the more anterior structure.

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Fig. 8.-A-D, Sequence of four transverse sonograms In one subject. Progressing In cephalocaudal direction, these were obtained at (A) and inferior to (B) portal vein origin, and at (C) and inferior to (D) level of crossing right renal artery (R). Posterior superior pancreaticoduodenal vein (curved arrows) Is 10cated posteromedial and nearly parallel to common bile duct (straight solid arrows). Note Insertion of posterior superior pancreaticoduodenal vein into portal vein (P) In A. Gastroduodenal artery (open arrows) remains in an anterior position on all images. v = supenor mesenteric vein, a = superior mesenteric artery, s = splenic vein, C = Inferior vena cava, A = aorta, g = gallbladder neck.

In nine cases (18%), the PSPDV inserted on the anterior aspect of the portal vein, closely mimicking the common bile duct. In all cases of an anteriorly inserting PSPDV (the configunation most likely to mimic the common bile duct), its oblique course facilitated visualization of flow with Doppler techniques. Inability to demonstrate flow occurred exclusively when the PSPDV inserted posteriorly into the portal vein, so that confusion with the common bile duct was unlikely in any event, despite absence of Doppler evidence of flow. Other tubular structures that may traverse the pancreatic head region and generate confusion are a caudalby inserting cystic duct and a replaced night hepatic artery. When fobbowed infenionly, the cystic duct will be noted to merge with the common duct [12], whereas the PSPDV will not. A replaced right hepatic artery intersects the PSPDV and common bile duct at a relatively large angle, and therefore is seen en face on sagittal images (Fig. 9). The PSPDV is occasionally duplicated such that one branch lies anterior to the duct and the other courses postenionly [4, 5], as occurred in one case in this series. If the antenon inferior pancneaticoduodenal vein is absent on diminutive, venous drainage of the anteroinfenion pancreas usually occurs via the PSPDV, as was also noted on one occasion [4, 5]. Visualization and demonstration of flow within the PSPDV in the current study is most likely attributable to improve-

Fig. 9.-Sonognam shows posterior superior pancreaticoduodenal vein (straight solid arrows) coursing anterior to common bile duct (curved arrow), which could be followed into porta hepatis. Left (arrowhead) and right (open arrow) hepatic arteries are separate. Venous flow within posterior superior pancreaticoduodenal vein is confirmed with pulsed Doppler tracing. P = portal vein, C = inferior vena cava.

ments

in high-resolution

sonognaphic

to pulsed and colon Doppler techniques slow blood flow in small visceral veins.

equipment,

capable

as well

of showing

as

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May 1993

SUPERIOR

PANCREATICODUODENAL

In this study, with the long axis of the inferior vena cava indicating the midcononal plane of the portal vein on sagittal sonograms, the PSPDV inserted on the anterior aspect of the portal vein in 18% of cases. This is at odds with reports of anatomic dissections and phlebographic studies in which exclusively posterior PSPDV insertion was observed [4, 5]. The reasons for this discrepancy are unclear. The orientation of PSPDV insertion was not observed to change with nespiration. In conclusion, the PSPDV may be imaged routinely when the pancreatic head is optimally seen at sonographic examination, and it can mimic the adjacent common bile duct in a significant minority of cases. Accurate identification of the common bile duct in such persons is necessary to ensure that the PSPDV is not the structure imaged. The common bile duct continues into the porta hepatis, whereas the PSPDV merges with the portal vein. When both are imaged, the common bile duct nearby always lies anterior to the PSPDV. If necessary, Doppler examination at slow-flow settings will show flow in an obliquely oriented PSPDV and absence of flow in the common bile duct. Awareness of the existence and anatomy of the PSPDV minimizes its confusion with the common bile duct during sonographic examination. ACKNOWLEDGMENTS I thank Solomon

Kyunghee

C. Cho, Bruce

for assistance

in manuscript

R. Javors, preparation;

and Robert Cebestia

W.

C. Con-

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way, Mary D. Jones, Sandra A. McDonald, and Anila D. Mehta for their sonographic skills and cooperation; Fred Ross for photographic expertise; and Denise A. Netta and Robert E. McBride for artistic contributions. REFERENCES 1. Laing FC. The gallbladder and bile ducts. In: Rumack CM, Wilson SR, Charbonoau Jw, eds. Diagnostic ultrasound. St. Louis: Mosby, 1991: 106-144 2. Cronan J. Ultrasound diagnosis of choledocholithiasis: a reappraisal. Radiology 1986;161 :133-134 3. Callon Pw, Mahony BS. Gallbladder and bile ducts. In: Vogler JB, Helms CA, Callen PW, eds. Normal variants andpitfalls in imaging. Philadelphia: Saunders, 1986:288-297 4. Falconen CWA, Griffiths E. The anatomy of the blood-vessels in the region of the pancreas. BrJ Surg 1950;37:334-344 5. Roichandt W, Cameron R. Anatomy of the pancreatic veins: a postmortem and clinical phlebognaphic investigation. Acta Radioll98O;21:33-41 6. Zirinsky K, Auh YH, Rubenstein WA, Kneeland BJ, Whalen JP, Kazam E. The portacaval space: CT with MR correlation. Radiologyl98s;156:453-460 7. Mori H, Miyake H, Aikawa H, et al. Dilated posterior superior pancreaticoduodenal vein: recognition with CT and clinical significance in patients with pancreaticobiliary carcinomas. Radiology 1991 181:793-800 8. Koonigsbung M, Hoffman-Trotin J. Abdominal sonography. Now York: Lippincott, 1991:3.4 9. Hollinshead WH. Anatomy for surgeons. Now York: Harper & Row, 1956: 382-466 10. Anson BJ, Mcvay C. Surgical anatomy. Philadelphia: Saunders, 1971: 546-722 11. Brooks JR. Surgery of the pancreas. Philadelphia: Saunders, 1983:1-23 1 2. Panulekar 5G. Sonography of the distal cystic duct. J Ultrasound Med 1989;8:367-373