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CT Assessment of the Inferior Peripancreatic Veins

Clinical Significance

¹ All authors: Department of Radiology, Oita Medical University, 1-1 Idaigaoka, Hasama-machi, Oita 879-5593, Japan.

Received February 8, 1999; accepted after revision August 11, 1999.

 
Address correspondence to Y. Yamada.

Abstract

Top Abstract Introduction Materials and Methods Results Discussion References

 
OBJECTIVES. The purpose of this study was to evaluate and clarify the clinical significance of CT scans of the inferior peripancreatic veins.

MATERIALS AND METHODS. Forty-three patients with suspected pancreatic disease underwent three-phase helical CT (collimation, 5 mm; reconstruction, 2.5 mm; scan delay, 30, 60, and 150 sec). The frequency of visualization on CT of the anterior and posterior inferior pancreaticoduodenal veins, inferior pancreaticoduodenal vein, and first jejunal trunk was assessed and correlated with angiographic and pathologic findings.

RESULTS. The frequency of visualization of normal inferior peripancreatic veins in patients (n = 22) with a normal portomesenteric vein was 36% for the anteroinferior pancreaticoduodenal vein, 36% for the posteroinferior pancreaticoduodenal vein, 59% for the inferior pancreaticoduodenal vein, and 100% for the first jejunal trunk. The smaller inferior peripancreatic veins were frequently not visualized when normal. In patients (n = 13) with pancreatic carcinoma involving the portosuperior mesenteric vein, all of the inferior peripancreatic veins were dilated and easily recognizable. When the tumor did not involve the portosuperior mesenteric vein but did involve the anteroinferior pancreaticoduodenal, posteroinferior pancreaticoduodenal, and inferior pancreaticoduodenal veins (n = 8), some of the other peripancreatic veins (first jejunal trunk, anterior and posterior superior pancreaticoduodenal veins, and gastrocolic trunk) were dilated. Dilatation indicated tumor extension to the third portion of the duodenum. In patients (n = 7) with involvement of the inferior pancreaticoduodenal vein, the first jejunal trunk, or both without the involvement of the portosuperior mesenteric vein, dilatation of the other peripancreatic veins (anteroinferior pancreaticoduodenal vein, posteroinferior pancreaticoduodenal vein, anterosuperior pancreaticoduodenal vein, posterosuperior pancreaticoduodenal vein, and gastrocolic trunk) indicated tumor invasion of only the second portion of the extrapancreatic nerve plexus (n = 4) and tumor invasion of both the second portion of the extrapancreatic nerve and the mesenteric root (n = 3).

CONCLUSION. Dilatation of peripancreatic veins with nonvisualization of inferior peripancreatic veins suggests tumor invasion of peripancreatic tissue.

Introduction

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The pancreas is located in the retroperitoneum and is contiguous to the portosuperior mesenteric vein and the superior mesenteric artery; therefore, pancreatic carcinoma easily invades the retroperitoneal tissues, including the extrapancreatic nerve plexus. The invasion of the extrapancreatic nerve plexus is found at surgery in 91% of patients with pancreatic carcinoma, making such invasion an important prognostic factor [1]. Although the prognosis of pancreatic carcinoma is poor (overall 5-year survival rate, approximately 12%), surgical resection remains the only potential cure [2, 3]. Accurate preoperative assessment of resectability and staging of pancreatic carcinoma is essential. CT findings of dilatation or obstruction of the superior peripancreatic veins (anterosuperior pancreaticoduodenal vein, posterosuperior pancreaticoduodenal vein, and gastrocolic trunk) suggest tumor extension to the peripancreatic tissues [4,5,6]. However, little has been reported about the inferior peripancreatic veins (anteroinferior pancreaticoduodenal vein, posteroinferior pancreaticoduodenal vein, inferior pancreaticoduodenal vein, and first jejunal trunk) because these small veins are difficult to detect on conventional CT [7]. Capable of scanning rapidly and producing detailed images of the pancreas, helical CT enables a more precise identification of the inferior peripancreatic veins.

The purpose of this study was to assess the frequency of helical CT visualization of normal inferior peripancreatic veins and to clarify the clinical significance of abnormal inferior peripancreatic veins.

Materials and Methods

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From November 1994 to June 1998, 43 patients (26 men and 17 women; age range, 24-78 years; mean age, 60.7 years) with clinically suspected pancreatic disease underwent three-phase helical CT. All patients underwent surgical resection and the pathologic diagnoses included pancreatic carcinoma (n = 24), bile duct carcinoma (n = 7), ampullary carcinoma (n = 5), chronic pancreatitis (n = 2), and others (n = 5).

Scanning Technique
Helical CT was performed on a HiSpeed Advantage scanner (General Electric Medical Systems, Milwaukee, WI). Initial unenhanced CT with 10mm collimation was performed to localize the pancreas. Helical CT was performed from the porta hepatis to the level just below the pancreatic head before and after IV administration of contrast material. Helical scanning parameters were 120 kVp, 200-250 mA, 5-mm collimation, 1:1 pitch, and 2.5mm overlapping reconstruction. A total of 100 ml of iopamidol (Iopamiron 300; Schering, Tokyo, Japan) was injected at a rate of 3 ml/sec with a power injector. After the injection of contrast material, three-phase helical CT images were obtained at 30 sec for the arterial phase, 60 sec for the portal venous phase, and 150 sec for the delayed phase.

Image Analysis
The normal CT anatomy of the inferior peripancreatic veins has been determined by helical CT using selective pancreatic arteriography [8]. Helical CT using selective pancreatic arteriography was performed during the injection of contrast material into the pancreaticoduodenal artery. The contrast material consisted of 75 mg I (iopamidol)/100 ml of saline solution. Five to 12 ml of the contrast material (Iopamiron 300) was administered at a rate of 0.6-2 ml/sec using a power injector.

The normal CT anatomy of the inferior peripancreatic veins on helical CT using selective pancreatic arteriography is shown in Figure 1A,1B,1C,1D, and schematic drawings are presented in Figure 2A,2B,2C,2D,2E. The anteroinferior pancreaticoduodenal vein is contiguous to the anterosuperior pancreaticoduodenal vein at the anterosulcus of the pancreas and passes between the inferior surface of the pancreatic head and the third portion of the duodenum. The posteroinferior pancreaticoduodenal vein is contiguous to the posterosuperior pancreaticoduodenal vein, originates in the duodenopancreatic sulcus below the common bile duct, and passes transversely above the anteroinferior pancreaticoduodenal vein. The anteroinferior pancreaticoduodenal vein and posteroinferior pancreaticoduodenal vein join to form the inferior pancreaticoduodenal vein, which drains into the first jejunal trunk, which then drains into the superior mesenteric vein after passing posterior to the superior mesenteric artery.

View larger version (176K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1A. —Normal CT anatomy of inferior peripancreatic veins in 56-year-old man with ampullary carcinoma. A—D, Selective pancreatic arteriogram (A) and three consecutive helical CT images using selective pancreatic arteriography (B—D) reveal normal anatomy of inferior peripancreatic veins. Anteroinferior pancreaticoduodenal vein (AI) passes between inferior surface of pancreatic head and third portion of duodenum. Posteroinferior pancreaticoduodenal vein (PI) passes transversely above AI. AI and PI join together to form inferior pancreaticoduodenal vein (IP), which drains into first jejunal trunk (JT), which then drains into superior mesenteric vein (SMV) after passing posterior to superior mesenteric artery (SMA). Note catheters in B—D (arrowheads). 1stD = first duodenal vein, PS = posterosuperior pancreaticoduodenal vein, GT = gastrocolic trunk, AS = anterosuperior pancreaticoduodenal vein, Du = duodenum. (Reprinted with permission from [8]).

View larger version (107K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1B. —Normal CT anatomy of inferior peripancreatic veins in 56-year-old man with ampullary carcinoma. A—D, Selective pancreatic arteriogram (A) and three consecutive helical CT images using selective pancreatic arteriography (B—D) reveal normal anatomy of inferior peripancreatic veins. Anteroinferior pancreaticoduodenal vein (AI) passes between inferior surface of pancreatic head and third portion of duodenum. Posteroinferior pancreaticoduodenal vein (PI) passes transversely above AI. AI and PI join together to form inferior pancreaticoduodenal vein (IP), which drains into first jejunal trunk (JT), which then drains into superior mesenteric vein (SMV) after passing posterior to superior mesenteric artery (SMA). Note catheters in B—D (arrowheads). 1stD = first duodenal vein, PS = posterosuperior pancreaticoduodenal vein, GT = gastrocolic trunk, AS = anterosuperior pancreaticoduodenal vein, Du = duodenum. (Reprinted with permission from [8]).

View larger version (110K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1C. —Normal CT anatomy of inferior peripancreatic veins in 56-year-old man with ampullary carcinoma. A—D, Selective pancreatic arteriogram (A) and three consecutive helical CT images using selective pancreatic arteriography (B—D) reveal normal anatomy of inferior peripancreatic veins. Anteroinferior pancreaticoduodenal vein (AI) passes between inferior surface of pancreatic head and third portion of duodenum. Posteroinferior pancreaticoduodenal vein (PI) passes transversely above AI. AI and PI join together to form inferior pancreaticoduodenal vein (IP), which drains into first jejunal trunk (JT), which then drains into superior mesenteric vein (SMV) after passing posterior to superior mesenteric artery (SMA). Note catheters in B—D (arrowheads). 1stD = first duodenal vein, PS = posterosuperior pancreaticoduodenal vein, GT = gastrocolic trunk, AS = anterosuperior pancreaticoduodenal vein, Du = duodenum. (Reprinted with permission from [8]).

View larger version (106K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1D. —Normal CT anatomy of inferior peripancreatic veins in 56-year-old man with ampullary carcinoma. A—D, Selective pancreatic arteriogram (A) and three consecutive helical CT images using selective pancreatic arteriography (B—D) reveal normal anatomy of inferior peripancreatic veins. Anteroinferior pancreaticoduodenal vein (AI) passes between inferior surface of pancreatic head and third portion of duodenum. Posteroinferior pancreaticoduodenal vein (PI) passes transversely above AI. AI and PI join together to form inferior pancreaticoduodenal vein (IP), which drains into first jejunal trunk (JT), which then drains into superior mesenteric vein (SMV) after passing posterior to superior mesenteric artery (SMA). Note catheters in B—D (arrowheads). 1stD = first duodenal vein, PS = posterosuperior pancreaticoduodenal vein, GT = gastrocolic trunk, AS = anterosuperior pancreaticoduodenal vein, Du = duodenum. (Reprinted with permission from [8]).

View larger version (102K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2A. —Schematic drawings show angiogram (A) and corresponding CT images (B—D) of normal inferior peripancreatic veins. panc. = pancreas, Du = duodenum, IVC = inferior vena cava, Ao = aorta. Angiographic image shows relationship of normal peripancreatic veins, portosuperior mesenteric vein, and superior mesenteric artery. The horizontal lines are correlated to images B—E.

View larger version (81K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2B. —Schematic drawings show angiogram (A) and corresponding CT images (B—D) of normal inferior peripancreatic veins. panc. = pancreas, Du = duodenum, IVC = inferior vena cava, Ao = aorta. Posterosuperior pancreaticoduodenal vein (PS) accompanies common bile duct (CBD). Gastrocolic trunk (GT) drains into right anterolateral aspect of superior mesenteric vein (SMV).

View larger version (88K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2C. —Schematic drawings show angiogram (A) and corresponding CT images (B—D) of normal inferior peripancreatic veins. panc. = pancreas, Du = duodenum, IVC = inferior vena cava, Ao = aorta. Anterosuperior pancreaticoduodenal vein (AS) is joined by right gastroepiploic vein (RGE) and right superior colic vein (RCV) to form GT.

View larger version (81K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2D. —Schematic drawings show angiogram (A) and corresponding CT images (B—D) of normal inferior peripancreatic veins. panc. = pancreas, Du = duodenum, IVC = inferior vena cava, Ao = aorta. Anteroinferior pancreaticoduodenal vein (AI) is contiguous to AS at anterosulcus of pancreas. Posteroinferior pancreaticoduodenal vein (PI) originates below CBD and passes transversely above AI. AI and PI join together to form inferior pancreaticoduodenal vein (IP), which drains into first jejunal trunk (JT), which then drains into SMV after passing posterior to superior mesenteric artery (SMA).

View larger version (79K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2E. —Schematic drawings show angiogram (A) and corresponding CT images (B—D) of normal inferior peripancreatic veins. panc. = pancreas, Du = duodenum, IVC = inferior vena cava, Ao = aorta. Anteroinferior pancreaticoduodenal vein (AI) is contiguous to AS at anterosulcus of pancreas. Posteroinferior pancreaticoduodenal vein (PI) originates below CBD and passes transversely above AI. AI and PI join together to form inferior pancreaticoduodenal vein (IP), which drains into first jejunal trunk (JT), which then drains into SMV after passing posterior to superior mesenteric artery (SMA).

The helical CT findings were interpreted with consensus of three radiologists who were knowledgeable of the anatomy of inferior peripancreatic veins. The radiologists were unaware of the surgical pathology and the results of other relevant imaging studies. The three-phase helical CT images were retrospectively reviewed to assess three conditions. The first condition was the frequency of visualization and diameter of the normal peripancreatic veins in patients without tumor involvement of the peripancreatic veins and the portosuperior mesenteric vein (control group). The second condition was the relationship of abnormalities of the inferior peripancreatic veins to tumor involvement of the portosuperior mesenteric vein. The third condition was the relationship of the abnormalities of the inferior peripancreatic veins to the tumor extension of the peripancreatic tissues (i.e., the duodenum, the extrapancreatic nerve plexus, and the mesenteric root). The maximum diameter of the visualized peripancreatic veins was measured at the phase with the most enhancement using digital calipers on magnified CT console images. The peripancreatic veins were defined as abnormally dilated if the maximum diameter was greater than the measurement of each normal peripancreatic vein in the control group. In addition, the appearance of the peripancreatic veins and portosuperior mesenteric vein on angiography and helical CT using selective pancreatic arteriography were correlated with the helical CT findings, and the tumor extension to the peripancreatic tissues was assessed by referring to the surgical pathology report.

Statistical Analysis
The chi-square test was used to compare the frequency of visualization of the peripancreatic veins between the group with and the group without tumor involvement of the portosuperior mesenteric vein. The t test was used to compare the mean diameter of visualized peripancreatic veins between the same two groups. Differences with a p value of less than 0.05 were considered statistically significant.

Results

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Based on the angiographic and surgical pathology findings, patients with pancreatic disease were classified into three groups with respect to the peripancreatic veins and the portosuperior mesenteric vein.

Patients with Normal Peripancreatic Veins and Portosuperior Mesenteric Vein (Control Group)
This control group consisted of 22 patients without tumor involvement of the peripancreatic tissues, including the peripancreatic veins and the portosuperior mesenteric vein on angiography and surgical pathology. The diagnoses of these patients included pancreatic carcinoma (n = 3), bile duct carcinoma (n = 7), ampullary carcinoma (n = 5), chronic pancreatitis (n = 2), mucinous cystadenoma of the pancreas (n = 3), serous cystadenoma of the pancreas (n = 1), and insulinoma of the pancreas (n = 1).

The frequency of visualization and the mean diameter of the normal peripancreatic veins on helical CT are summarized in Table 1. The inferior peripancreatic veins were identified in the 22 patients of the control group with the following frequencies: 36% for the anteroinferior pancreaticoduodenal vein (mean diameter ± SD, 1.4 ± 0.5 mm; size range, 1-2 mm), 36% for the posteroinferior pancreaticoduodenal vein (1.5 ± 0.5 mm; 1-2 mm), 59% for the inferior pancreaticoduodenal vein (1.6 ± 0.5 mm; 1-2 mm), and 100% for the first jejunal trunk (4.5 ± 1.1 mm; 2-7 mm). The superior peripancreatic veins were identified in the same 22 patients with the following frequencies: 100% for the gastrocolic trunk (3.8 ± 0.8 mm; 2-5 mm), 95% for the posterosuperior pancreaticoduodenal vein (2.6 ± 0.7 mm; 1-4 mm), and 50% for the anterosuperior pancreaticoduodenal vein (1.6 ± 0.6 mm; 1-3 mm). The results of this control group were used as a reference for normal-sized veins. The inferior peripancreatic veins were assessed as abnormally dilated when the diameter exceeded 2 mm for the anteroinferior pancreaticoduodenal vein, posteroinferior pancreaticoduodenal vein, and inferior pancreaticoduodenal vein; 7 mm for the first jejunal trunk; 5 mm for the gastrocolic trunk; 4 mm for the posterosuperior pancreaticoduodenal vein; and 3 mm for the anterosuperior pancreaticoduodenal vein.

The inferior peripancreatic veins and gastrocolic trunk were most enhanced at the second phase (Fig. 3A,3B,3C,3D). The posterosuperior pancreaticoduodenal vein and the anterosuperior pancreaticoduodenal vein were most enhanced at the first phase (Table 1).

View larger version (137K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3A. —74-year-old woman with ampullary cancer and normal peripancreatic veins. A—D, Second phase of contrast-enhanced helical CT. Scans show inferior peripancreatic veins—anteroinferior pancreaticoduodenal vein (AI), posteroinferior pancreaticoduodenal vein (PI), inferior pancreaticoduodenal vein (IP), and first jejunal trunk (JT)—and gastrocolic trunk (GT) as mostly enhanced. Note drainage tube (arrowheads). SMV = superior mesenteric vein, SMA = superior mesenteric artery.

View larger version (126K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3B. —74-year-old woman with ampullary cancer and normal peripancreatic veins. A—D, Second phase of contrast-enhanced helical CT. Scans show inferior peripancreatic veins—anteroinferior pancreaticoduodenal vein (AI), posteroinferior pancreaticoduodenal vein (PI), inferior pancreaticoduodenal vein (IP), and first jejunal trunk (JT)—and gastrocolic trunk (GT) as mostly enhanced. Note drainage tube (arrowheads). SMV = superior mesenteric vein, SMA = superior mesenteric artery.

View larger version (137K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3C. —74-year-old woman with ampullary cancer and normal peripancreatic veins. A—D, Second phase of contrast-enhanced helical CT. Scans show inferior peripancreatic veins—anteroinferior pancreaticoduodenal vein (AI), posteroinferior pancreaticoduodenal vein (PI), inferior pancreaticoduodenal vein (IP), and first jejunal trunk (JT)—and gastrocolic trunk (GT) as mostly enhanced. Note drainage tube (arrowheads). SMV = superior mesenteric vein, SMA = superior mesenteric artery.

View larger version (131K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3D. —74-year-old woman with ampullary cancer and normal peripancreatic veins. A—D, Second phase of contrast-enhanced helical CT. Scans show inferior peripancreatic veins—anteroinferior pancreaticoduodenal vein (AI), posteroinferior pancreaticoduodenal vein (PI), inferior pancreaticoduodenal vein (IP), and first jejunal trunk (JT)—and gastrocolic trunk (GT) as mostly enhanced. Note drainage tube (arrowheads). SMV = superior mesenteric vein, SMA = superior mesenteric artery.

Patients with Involvement of the Portosuperior Mesenteric Vein Above the Level of Entry of the Inferior Pancreaticoduodenal Vein
This group consisted of 13 patients with carcinoma of the head of the pancreas. In all patients, the involvement of the portosuperior mesenteric vein above the level of entry of the inferior pancreaticoduodenal vein was confirmed by the angiographic and surgical pathology findings. In this group, 10 patients had tumor involvement of some peripancreatic veins on angiography and surgical pathology. Thus, the frequency of visualization of the peripancreatic veins was determined by the number of peripancreatic veins without tumor involvement.

The frequency of visualization of the inferior peripancreatic veins was 90% for the anteroinferior pancreaticoduodenal vein and 100% for the posteroinferior pancreaticoduodenal vein, inferior pancreaticoduodenal vein, and first jejunal trunk (Table 2). The frequency of visualization of the anteroinferior pancreaticoduodenal vein (90%), posteroinferior pancreaticoduodenal vein (100%), and inferior pancreaticoduodenal vein (100%) was significantly greater than those in the control group (p < 0.05). The frequency of visualization of the first jejunal trunk was similar to that of the control group. The mean diameter of the inferior pancreaticoduodenal vein was significantly greater in this group than in the control group (p < 0.05). The differences in the mean diameter of the anteroinferior pancreaticoduodenal vein, posteroinferior pancreaticoduodenal vein, and first jejunal trunk between this group and the control group was not statistically significant. Of the visualized veins, the following were dilated: zero (0%) of nine visualized anteroinferior pancreaticoduodenal veins, one (10%) of 10 visualized posteroinferior pancreaticoduodenal veins, four (40%) of 10 visualized inferior pancreaticoduodenal veins, and two (20%) of 10 visualized first jejunal trunks.

The frequency of visualization of the superior peripancreatic veins was 100%. The frequency of visualization of the anterosuperior pancreaticoduodenal vein was significantly greater than that in the control group (p < 0.05). The frequency of visualization of the gastrocolic trunk and posterosuperior pancreaticoduodenal vein was similar to that of the control group. The mean diameters of the gastrocolic trunk, posterosuperior pancreaticoduodenal vein, and anterosuperior pancreaticoduodenal vein were significantly greater than those in the control group (p < 0.05). Of the visualized veins, the following number were dilated: two (25%) of eight visualized gastrocolic trunks, five (56%) of nine visualized posterosuperior pancreaticoduodenal veins, and one (10%) of 10 visualized anterosuperior pancreaticoduodenal veins.

Patients with Involvement of the Inferior Peripancreatic Veins with Normal Portosuperior Mesenteric Vein
Eight patients with caricinoma of the head of the pancreas were included in this group. In all patients, obstruction of any of the inferior peripancreatic veins was confirmed on angiography and surgical pathology, and these obstructed veins were not visualized on helical CT. The peripancreatic veins, except for the veins obstructed by tumor, were all recognized. Dilated veins were identified as follows: two (100%) of two visualized anteroinferior pancreaticoduodenal veins, one (100%) of one visualized inferior pancreaticoduodenal vein, two (33%) of six visualized first jejunal trunks, six (75%) of eight visualized gastrocolic trunks, four (80%) of five visualized posterosuperior pancreaticoduodenal veins, and four (57%) of seven visualized anterosuperior pancreaticoduodenal veins. In each patient, at least one of the peripancreatic veins (except for the veins obstructed by tumor) was abnormally dilated.

Surgical pathology revealed tumor extension to the third portion of the duodenum in all eight patients (Fig. 4A,4B,4C,4D,4E,4F), tumor extension to the second portion of the extrapancreatic nerve plexus in seven (88%) of eight patients (Fig. 4A,4B,4C,4D,4E,4F), and tumor extension to the mesenteric root in three (38%) of eight patients.

View larger version (164K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4A. —67-year-old man with carcinoma of pancreatic head. A—D, Helical CT scans show dilatation of gastrocolic trunk (GT) (6 mm) and posterosuperior pancreaticoduodenal vein (PS) (5 mm) that resulted from tumor invasion of anteroinferior pancreaticoduodenal vein (AI), posteroinferior pancreaticoduodenal vein (PI), and inferior pancreaticoduodenal vein (IP). Portosuperior mesenteric vein is normal. Note drainage tube (arrowhead) in A and B. AS = anterosuperior pancreaticoduodenal vein, SMV = superior mesenteric vein, SMA = superior mesenteric artery, JT = first jejunal trunk, Ca = carcinoma.

View larger version (161K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4B. —67-year-old man with carcinoma of pancreatic head. A—D, Helical CT scans show dilatation of gastrocolic trunk (GT) (6 mm) and posterosuperior pancreaticoduodenal vein (PS) (5 mm) that resulted from tumor invasion of anteroinferior pancreaticoduodenal vein (AI), posteroinferior pancreaticoduodenal vein (PI), and inferior pancreaticoduodenal vein (IP). Portosuperior mesenteric vein is normal. Note drainage tube (arrowhead) in A and B. AS = anterosuperior pancreaticoduodenal vein, SMV = superior mesenteric vein, SMA = superior mesenteric artery, JT = first jejunal trunk, Ca = carcinoma.

View larger version (157K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4C. —67-year-old man with carcinoma of pancreatic head. A—D, Helical CT scans show dilatation of gastrocolic trunk (GT) (6 mm) and posterosuperior pancreaticoduodenal vein (PS) (5 mm) that resulted from tumor invasion of anteroinferior pancreaticoduodenal vein (AI), posteroinferior pancreaticoduodenal vein (PI), and inferior pancreaticoduodenal vein (IP). Portosuperior mesenteric vein is normal. Note drainage tube (arrowhead) in A and B. AS = anterosuperior pancreaticoduodenal vein, SMV = superior mesenteric vein, SMA = superior mesenteric artery, JT = first jejunal trunk, Ca = carcinoma.

View larger version (158K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4D. —67-year-old man with carcinoma of pancreatic head. A—D, Helical CT scans show dilatation of gastrocolic trunk (GT) (6 mm) and posterosuperior pancreaticoduodenal vein (PS) (5 mm) that resulted from tumor invasion of anteroinferior pancreaticoduodenal vein (AI), posteroinferior pancreaticoduodenal vein (PI), and inferior pancreaticoduodenal vein (IP). Portosuperior mesenteric vein is normal. Note drainage tube (arrowhead) in A and B. AS = anterosuperior pancreaticoduodenal vein, SMV = superior mesenteric vein, SMA = superior mesenteric artery, JT = first jejunal trunk, Ca = carcinoma.

View larger version (80K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4E. —67-year-old man with carcinoma of pancreatic head. Photomicrograph shows tumor extension (arrow) to third portion of duodenum (Du). Ca = carcinoma (H and E, x1)

View larger version (135K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4F. —67-year-old man with carcinoma of pancreatic head. High-power photomicrograph shows neural invasion to second portion of extrapancreatic nerve plexus. Note cancer cells (arrows) in perineural space. N = nerve. (H and E, x100)

Discussion

Top Abstract Introduction Materials and Methods Results Discussion References

 
Recent advances in radiologic imaging, particularly in helical CT, have made it possible to assess the normal pancreatic and peripancreatic anatomy [9, 10]. These assessments contribute to the accurate diagnosis and staging of pancreatic carcinoma.

CT findings of tumor extension to the extrapancreatic tissue have been reported to include obliteration of the periarterial fat, tumor-vessel contiguity, and soft-tissue infiltration of peripancreatic structures [11,12,13]. Mori et al. [4, 5] first described the normal CT anatomy of the superior peripancreatic veins and reported that abnormalities of peripancreatic veins on conventional CT could be used as additional evidence of extrapancreatic extension.

The frequency of visualization of the superior peripancreatic veins in patients with normal portosuperior mesenteric veins using thin-section helical CT (3-mm collimation; 100 ml of contrast material injected at 2 ml/sec; 60-sec scan delay) was first reported by Ibukuro et al. [9]. According to their report, the gastrocolic trunk, posterosuperior pancreaticoduodenal vein, anterosuperior pancreaticoduodenal vein, and first jejunal trunk were seen in 100%, 72%, 52%, and 96% of their patients, respectively. The results in our control group were similar to their results (100% for the gastrocolic trunk, 95% for the posterosuperior pancreaticoduodenal vein, 50% for the anterosuperior pancreaticoduodenal vein, and 100% for the first jejunal trunk).

To our knowledge, only one report in English literature on the inferior peripancreatic veins discusses the frequency of visualization of the first jejunal trunk [10], and no studies have been reported on the other inferior peripancreatic veins. However, confirmation of the normal CT anatomy of inferior peripancreatic veins by helical CT using selective pancreatic arteriography has been reported by Hori et al. [8] (Figs. 1A,1B,1C,1D, 2A,2B,2C,2D,2E, and 5 A). With this knowledge of the normal CT anatomy, we evaluated the frequency of visualization and mean diameter of normal and abnormal inferior peripancreatic veins on thin-section helical CT scans.

View larger version (87K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5A. —Illustrations show CT findings of normal anatomy of peripancreatic veins and features in tumor invasion of peripancreatic tissues. Drawing shows CT findings of normal anatomy of peripancreatic veins and second portion of extrapancreatic nerve plexus. Paired pancreaticoduodenal venous arcades, anterior arcade—anterosuperior pancreaticoduodenal vein (AS) and anteroinferior pancreaticoduodenal vein (AI)—and posterior arcade—posterosuperior pancreaticoduodenal vein (PS) and posteroinferior pancreaticoduodenal vein (PI)—lie directly on surface of pancreatic head. Inferior pancreaticoduodenal vein (IP) and first jejunal trunk (JT) run behind superior mesenteric artery (SMA). Note area of small circles representing extrapancreatic nerve plexus. RCV = right superior colic vein, RGE = right gastroepiploic vein, GT = gastrocolic trunk, SMV = superior mesenteric vein, Panc. = pancreas.

In patients with normal peripancreatic veins and a normal portosuperior mesenteric vein (control group), the frequencies of visualization of the anteroinferior pancreaticoduodenal vein (36%) and posteroinferior pancreaticoduodenal vein (36%) were lower than those of the other inferior peripancreatic veins (inferior pancreaticoduodenal vein, 59%; first jejunal trunk, 100%) and those of the superior peripancreatic veins (gastrocolic trunk, 100%; posterosuperior pancreaticoduodenal vein, 95%; anterosuperior pancreaticoduodenal vein, 50%). This low frequency is probably a result of the small diameters of the anteroinferior pancreaticoduodenal vein and posteroinferior pancreaticoduodenal vein or a result of the complex anatomic relationship and oblique courses of the anteroinferior pancreaticoduodenal vein and the posteroinferior pancreaticoduodenal vein, which run between the pancreatic head and the third portion of the duodenum.

The peripancreatic veins were measured during the phase of greatest enhancement for each vein. The inferior peripancreatic veins and gastrocolic trunk were noted to be most enhanced in the second phase, but the superior peripancreatic veins (except for the gastrocolic trunk) were most enhanced in the first phase. The difference might be a result of the circulation time in the pancreas and gastrointestinal tract (i.e., stomach, duodenum, jejunum, and colon). The peripancreatic veins were not evaluated in the third phase because they could rarely be visualized at that time.

Tumor involvement of the portosuperior mesenteric vein is one of the crucial determinants of surgical resectability of pancreatic carcinoma. Resection and reconstruction of the portosuperior mesenteric vein have now become safe procedures [14, 15]. Preoperative evaluation of tumor involvement of the portosuperior mesenteric vein is important because resection is difficult, requiring appropriate planning and mobilization of available resources.

According to Mori et al. [4], a dilated posterosuperior pancreaticoduodenal vein indicates that the tumor has extended to the wall of the portosuperior mesenteric vein; the posterosuperior pancreaticoduodenal vein might dilate as a result of being a hepatopetal collateral vein after occlusive changes of the portosuperior mesenteric vein.

In all our patients with tumor involvement of the portosuperior mesenteric vein above the level of entry of the inferior pancreaticoduodenal vein, the frequencies of visualization of the anteroinferior pancreaticoduodenal vein, posteroinferior pancreaticoduodenal vein, and inferior pancreaticoduodenal vein were significantly greater than those of the control group (anteroinferior pancreaticoduodenal vein, 36% in control group versus 90% in this group; posteroinferior pancreaticoduodenal vein, 36% in control group versus 100% in this group; inferior pancreaticoduodenal vein, 59% in control group versus 100% in this group) and these inferior peripancreatic veins were abnormally dilated in five (17%) of 29 veins (Table 2). However, the difference in the frequency of visualization of the first jejunal trunk between this group and the control group was not statistically significant. The inferior peripancreatic veins were considered to be the collateral pathway because the involvement of the portosuperior mesenteric vein can cause retrograde flow from the portosuperior mesenteric vein to the inferior peripancreatic veins (Fig. 5B). Because the frequency of visualization of the anteroinferior pancreaticoduodenal vein, posteroinferior pancreaticoduodenal vein, and inferior pancreaticoduodenal vein was low and these veins were not always visualized in the control group, when visualized, dilated, or both on helical CT in patients with pancreatic carcinoma, tumor invasion of the portosuperior mesenteric vein should be considered, even though angiography or helical CT may show normal findings of the portosuperior mesenteric vein.

View larger version (106K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5B. —Illustrations show CT findings of normal anatomy of peripancreatic veins and features in tumor invasion of peripancreatic tissues. Drawing shows changes of peripancreatic veins in carcinomatous tumor involvement (Ca) of portosuperior mesenteric vein. When tumor involved portosuperior mesenteric vein, most inferior peripancreatic veins (AI, PI, and IP) were visualized and some were abnormally dilated.

In eight patients with normal portosuperior mesenteric veins and pathologically proven tumor involvement of any of the inferior peripancreatic veins, these obstructed veins were not visualized on helical CT. However, all of the other peripancreatic veins were visualized, and 19 (65%) of the 29 visualized peripancreatic veins were abnormally dilated. If any inferior peripancreatic veins were obstructed, at least one of the peripancreatic veins, especially the gastrocolic trunk and the posterosuperior pancreaticoduodenal vein, was dilated. All eight of these patients had pathologically proven tumor extension to the third portion of the duodenum, which suggests that the obstruction of the inferior peripancreatic veins is related to the anatomic location because the anteroinferior pancreaticoduodenal vein, posteroinferior pancreaticoduodenal vein, and inferior pancreaticoduodenal vein run between the inferior surface of the pancreatic head and the third portion of the duodenum. However, because the anteroinferior pancreaticoduodenal vein, posteroinferior pancreaticoduodenal vein, and inferior pancreaticoduodenal vein were not always visualized in the control group, nonvisualization of these veins cannot be used reliably to indicate local tumor extension. Therefore, dilatation of the other peripancreatic veins (first jejunal trunk, gastrocolic trunk, posterosuperior pancreaticoduodenal vein, and anterosuperior pancreaticoduodenal vein) with nonvisualization of the anteroinferior pancreaticoduodenal vein, posteroinferior pancreaticoduodenal vein, and inferior pancreaticoduodenal vein could indicate tumor extension to the third portion of the duodenum.

In seven of eight patients with normal portosuperior mesenteric veins and proven tumor involvement of any of the inferior peripancreatic veins, the tumor extension to the second portion of the extrapancreatic nerve plexus was confirmed on surgical pathology. Nerve plexus invasion is widely accepted to be a unique route for the spread of pancreatic carcinoma and has been found at surgery in 91% of patients [1]. Extrapancreatic nerve plexus invasion is one of the major causes of recurrence of surgically resected pancreatic carcinoma, and complete removal of this nerve plexus may prolong survival [16, 17]. However, little is known about CT findings of nerve plexus invasion. The extrapancreatic nerve plexus is divided into two main portions. The first portion extends from the right celiac ganglia to the upper median margin of the uncinate process of the pancreas, and the second portion extends from the superior mesenteric artery to the median margin of the uncinate process [18]. Invasion of the second portion is reported in 90% of cases of extrapancreatic nerve plexus invasion [19, 20]. Kaneko et al. [20] reported that on intraportal endovascular sonography, the hypoechoic area around the inferior pancreaticoduodenal artery indicated invasion of the second portion of the extrapancreatic nerve plexus because this artery is within the second portion of the extrapancreatic nerve plexus. The involvement of the inferior pancreaticoduodenal vein is considered to reflect tumor invasion of the second portion of the extrapancreatic nerve plexus because the inferior pancreaticoduodenal vein usually accompanies the inferior pancreaticoduodenal artery (Fig. 5C). Helical CT findings of invasion of the second portion of the extrapancreatic nerve plexus may guide surgeons in deciding whether to completely resect this nerve plexus. In all our patients, tumor involvement of the inferior pancreaticoduodenal vein was proven on surgical pathology to include tumor invasion of the second portion of the extrapancreatic nerve plexus. However, because the inferior pancreaticoduodenal vein was not always visualized in the control group, dilatation of other peripancreatic veins could indicate the occlusion of the inferior pancreaticoduodenal vein and tumor invasion of the second portion of the extrapancreatic nerve plexus.

View larger version (82K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5C. —Illustrations show CT findings of normal anatomy of peripancreatic veins and features in tumor invasion of peripancreatic tissues. Drawing shows changes of peripancreatic veins in carcinomatous tumor involvement (Ca) of second portion of extrapancreatic nerve plexus. Tumor involvement of any inferior peripancreatic veins (AI, PI, and IP) may have caused dilatation of other peripancreatic veins. Nonvisualization of IP, JT, or both with dilatation of other peripancreatic veins indicates tumor invasion of second portion of extrapancreatic nerve plexus and mesenteric root. Note directions of venous blood flow (arrows).

Although resection and reconstruction of the portal vein have become safe procedures, resection of the superior mesenteric artery still entails considerable risk [14, 21]. Tumor involvement of the superior mesenteric artery is a determinant for unresectability; thus, estimation of such infiltration is required. Tumor involvement of the superior mesenteric artery has been studied with CT to evaluate the circumferential contiguity of the tumor to the superior mesenteric artery, perivascular stranding, and superior mesenteric artery fat pad obliteration [11,12,13]. In this study, three of eight patients with proven tumor involvement of any of the inferior peripancreatic veins with normal portosuperior mesenteric vein were proved on surgical pathology to have tumor extension to the root of the superior mesenteric artery, which is the mesenteric root. Because the inferior pancreaticoduodenal vein and first jejunal trunk of the inferior peripancreatic veins usually pass closely behind the superior mesenteric artery, tumor involvement of the inferior pancreaticoduodenal vein and first jejunal trunk could be an indicator of tumor extension to the mesenteric root (Fig. 5C). The first jejunal trunk was always visualized; however, the inferior pancreaticoduodenal vein was not always visualized in the control group. Therefore, the nonvisualization of the first jejunal trunk, dilatation of the peripancreatic veins, or both with nonvisualization of the inferior pancreaticoduodenal vein suggest carcinomatous extension to the mesenteric root.

The main disadvantage of our scanning protocol is the limited scan range from the porta hepatis to the level just below the pancreatic head; the evaluation of metastases to the liver and paraaortic lymph nodes is insufficient. To evaluate such metastases, CT scans using a collimation of 7-8 mm, which permits full evaluation of the liver and paraaortic lymph nodes, and other imaging techniques are recommended.

In conclusion, knowledge of the CT anatomy of the inferior peripancreatic veins is important for the recognition of abnormalities in these veins. Thin-section helical CT may improve accuracy of the staging of pancreatic carcinoma, especially in the involvement of the third portion of the duodenum, the portosuperior mesenteric vein, the second portion of the extrapancreatic nerve plexus, and the mesenteric root.

References

Top Abstract Introduction Materials and Methods Results Discussion References

 

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