AJR 2005; 184:481-486
© American Roentgen Ray Society
Inferior Mesenteric Vein: Gray-Scale and Doppler Sonographic Findings in Normal Subjects and in Patients with Portal Hypertension
Ronald H. Wachsberg1
1 Department of Radiology, New Jersey Medical School, 150 Bergen St., c-320,
Newark, NJ 07103.
Received May 11, 2004;
accepted after revision July 22, 2004.
Address correspondence to R. H. Wachsberg
(wachsbrh{at}umdnj.edu).
Introduction
The inferior mesenteric vein (IMV) drains venous outflow from the
embryologic hindgut (i.e., distal transverse colon to proximal rectum) to the
portal system. Whereas radiologists are familiar with the cross-sectional
appearance of the IMV on CT and MRI
[1–3],
I know of no report of the sonographic appearance of the IMV, despite
descriptions of the sonographic features of the inferior mesenteric artery
[4,
5]. In our practice, the IMV is
routinely visualized on sonography when the pancreas is not obscured.
Familiarity with the sonographic anatomy of the IMV minimizes the risk that
this vessel will be mistakenly identified as the splenic vein and is useful in
the evaluation of patients with portal hypertension. This article presents the
sonographic appearance of the IMV in healthy subjects and in patients with
portal hypertension.
Normal Anatomy
The IMV originates anterior to the sacrum as the superior rectal
(hemorrhoidal) vein and receives branches from the sigmoid and descending
colon as it ascends to the left of midline, adjacent to the inferior
mesenteric artery and left gonadal vein. In the upper abdomen, the IMV passes
posterior to the distal duodenum, anterior to the left renal vein, and then
anterior to the superior mesenteric artery before anastomosing with the portal
venous system [1]. In a large
autopsy series, the IMV inserted into the distal splenic vein in 38.0%, the
portal confluence in 32.7%, and the superior mesenteric vein in 29.3% of cases
[6]. On CT, the diameter of the
normal IMV rarely exceeds 6 mm
[1].
Sonographic Anatomy
To obtain a long-axis sonogram of the upper abdominal IMV, the plane of
section is typically oblique, directed slightly toward the left lower
quadrant, whereas the long axis of the splenic vein is directed slightly
toward the left upper quadrant (Fig.
1). In our experience, the upper abdominal IMV is visualized on
sonography in most patients in whom the pancreatic body is not obscured. In
healthy subjects, Doppler interrogation reveals hepatopetal flow in both the
splenic vein and the IMV (Fig.
2A,
2B). Both veins invariably pass
anterior to the superior mesenteric artery, as opposed to jejunal veins, which
can pass either anterior or posterior to the superior mesenteric artery as
they cross the midline to join the superior mesenteric vein
(Fig. 3). The pelvic segment of
the IMV is usually obscured and therefore not amenable to visualization on
sonography in healthy subjects.
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Fig. 1. —Line drawing depicts inferior mesenteric vein (IMV) inserting
into portal system at confluence, a common configuration. Plane tangential to
splenic vein (dashed line) is directed toward left upper quadrant,
whereas plane tangential to IMV (solid line) is directed toward left
lower quadrant.
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Fig. 2A. —22-year-old man with abdominal pain and normal findings on
sonographic examination. Color Doppler sonogram tangential to long axis of
inferior mesenteric vein (IMV) shows hepatopetal blood flow within IMV, which
passes anterior to left renal vein and superior mesenteric artery (SMA) and
posterior to distal duodenum and pancreas.
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Fig. 2B. —22-year-old man with abdominal pain and normal findings on
sonographic examination. Color Doppler sonogram tangential to long axis of
splenic vein shows that it too passes anterior to SMA and has hepatopetal
blood flow.
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Fig. 3. —42-year-old woman with abdominal pain and normal findings on
sonographic examination. Transverse sonogram shows jejunal vein
(arrowheads) that passes anterior to duodenum (asterisks)
and superior mesenteric artery (SMA) before inserting into superior mesenteric
vein (SMV). Jejunal vein should not be mistakenly identified as inferior
mesenteric vein, which passes behind rather than anterior to distal duodenum.
IVC = inferior vena cava, AO = aorta.
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Correctly identifying the IMV is important in certain circumstances. In
particular, when examining patients with pancreatic disease, splenic vein
thrombosis cannot be excluded unless one is certain that a patent vein
identified is indeed the splenic vein rather than the IMV
(Fig. 4). In our experience,
the splenic vein and IMV are easily confused with one another by sonographers
unfamiliar with IMV anatomy. Confusion occurs because both the splenic vein
and IMV cross the midline anterior to the superior mesenteric artery, are
intimately related to the pancreas, and are often in close proximity to each
other.
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Fig. 4. —45-year-old man with chronic pancreatitis. Color Doppler
sonogram shows dilated pancreatic duct (pd). Note red color-flow signal in
blood vessel (arrowhead) that might be mistaken for patent splenic
vein, located between pancreas and superior mesenteric artery
(asterisk). In fact, splenic vein was thrombosed, and vessel
displayed is inferior mesenteric vein.
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Several findings are helpful to distinguish between the IMV and splenic
vein on sonography. In healthy subjects, the diameter of the splenic vein is
virtually always greater than or equal to the diameter of the IMV, and the IMV
is more intimately related to the left renal vein than is the splenic vein
(Fig. 5A,
5B). The splenic vein is
closely apposed to the entire pancreas, including the tail, whereas the IMV
lies posterior to the distal duodenum before passing behind the body of the
pancreas (Fig. 6). However, the
latter feature is not helpful if the pancreatic tail is obscured, if a
collapsed duodenum blends with the pancreas (Fig.
7A,
7B), or if a prominent left
colic vein passing behind the pancreatic tail simulates the splenic vein
(Fig. 8). Distention of the
stomach with degassed fluid, a technique for improving visualization of the
peripancreatic region, might facilitate distinction between the IMV and other
regional blood vessels, although to date we have not attempted the technique
for this application.
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Fig. 5A. —24-year-old woman with symptomatic gallstones. Long-axis
sonograms of splenic vein (white arrowhead) (A) and inferior
mesenteric vein (IMV, black arrowhead) (B) show that IMV lies
directly anteriorly to left renal vein (LRV). Splenic vein and IMV are
otherwise difficult to distinguish in this patient.
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Fig. 5B. —24-year-old woman with symptomatic gallstones. Long-axis
sonograms of splenic vein (white arrowhead) (A) and inferior
mesenteric vein (IMV, black arrowhead) (B) show that IMV lies
directly anteriorly to left renal vein (LRV). Splenic vein and IMV are
otherwise difficult to distinguish in this patient.
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Fig. 7A. —32-year-old man with abdominal pain and normal sonographic
findings. Midline sonogram through pancreas shows vessel (arrowhead)
that passes directly anterior to left renal vein (LRV), suggesting inferior
mesenteric vein (IMV). However, vessel seems to be closely applied to entire
pancreas, including pancreatic tail, which is more consistent with splenic
vein. Note that what appears to be pancreatic tail (asterisk) is
slightly less echogenic than head and body of pancreas.
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Fig. 7B. —32-year-old man with abdominal pain and normal sonographic
findings. Several minutes later, sonogram at same location reveals
intraluminal gas and secretions in duodenum (asterisk), which when
collapsed closely simulated pancreatic tail. If nondistended duodenum blends
with pancreas and cannot be discerned as a distinct organ, then IMV
(arrowhead) immediately posterior to duodenum may be mistakenly
identified as splenic vein.
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Fig. 8. —29-year-old woman with intermittent abdominal pain and normal
findings on sonographic examination. Transverse sonogram shows vessel
(white arrowhead) that courses behind tail of pancreas (P) and in
front of duodenum (D). Its close relationship to pancreatic tail suggests that
this is splenic vein. In fact, this is prominent left colic vein draining into
inferior mesenteric vein (black arrowheads).
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Findings in Portal Hypertension
Dilatation of the IMV (i.e., diameter > 6 mm) is an infrequent finding
in patients with portal hypertension
[3] (Fig.
9A,
9B). Among patients with
portal hypertension referred to our liver center for evaluation before
possible liver transplantation, approximately one in five has hepatofugal flow
in the IMV (unpublished observations). Indeed, we see occasional patients in
whom hepatofugal IMV flow is the most conspicuous sign of portal hypertension
(Fig. 10A,
10B). The IMV provides a
conduit for portosystemic shunting via two major pathways: communication with
the left gonadal vein (Fig.
11A,
11B) and communication with
the middle and inferior rectal (hemorrhoidal) veins (Fig.
12A,
12B,
12C,
12D).
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Fig. 9A. —44-year-old man with cirrhosis and portal hypertension. DUO =
duodenum, AO = aorta. Transverse sonogram shows dilated inferior mesenteric
vein (IMV) that measures 10 mm in diameter, a relatively uncommon finding in
portal hypertension, in our experience. Note that IMV is posterior to distal
duodenum.
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Fig. 10B. —46-year-old woman with cirrhosis and portal hypertension.
Duplex Doppler sonogram of inferior mesenteric vein (IMV) shows hepatofugal
flow. Note that IMV is not dilated. Because IMV was only major portal
tributary with hepatofugal flow, Doppler examination of IMV provided important
diagnostic information in this patient.
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Fig. 11A. —38-year-old woman with portal hypertension and portosystemic
communication between inferior mesenteric vein (IMV) and systemic rectal
venous drainage. Left parasagittal color Doppler sonogram at level of sacral
promontory shows hepatofugal flow in dilated IMV. Arrows indicate direction of
flow. CIA = left common iliac artery, CIV = left common iliac vein.
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Fig. 11B. —38-year-old woman with portal hypertension and portosystemic
communication between inferior mesenteric vein (IMV) and systemic rectal
venous drainage. Transverse color Doppler sonogram through distended bladder
shows perirectal varices.
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Fig. 12A. —39-year-old woman with portal hypertension and portosystemic
communication between inferior mesenteric vein (IMV) and left gonadal vein.
Coronal color Doppler sonogram of left flank shows hepatofugal flow in dilated
IMV adjacent to dilated left ovarian vein. Arrows indicate direction of
flow.
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Fig. 12B. —39-year-old woman with portal hypertension and portosystemic
communication between inferior mesenteric vein (IMV) and left gonadal vein.
Transverse color Doppler sonogram adjacent to lower abdominal aorta (AO)
reveals varices at site of communication between IMV and left gonadal
vein.
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Fig. 12C. —39-year-old woman with portal hypertension and portosystemic
communication between inferior mesenteric vein (IMV) and left gonadal vein.
Contrast-enhanced CT scan slightly caudal to left renal vein shows dilated IMV
and left gonadal vein (LGV).
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Fig. 12D. —39-year-old woman with portal hypertension and portosystemic
communication between inferior mesenteric vein (IMV) and left gonadal vein. CT
scan caudal to aortic bifurcation shows portosystemic varices (arrow)
at site of communication between IMV and left gonadal vein.
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In our experience evaluating patients with hepatofugal IMV flow who
subsequently undergo creation of a transjugular intrahepatic portosystemic
shunt (TIPS), postprocedural conversion to hepatopetal IMV flow is an
ancillary indicator of satisfactory TIPS function (Fig.
13A,
13B), although the efficacy of
this sign as an indicator of TIPS function has not been established in a
formal study.
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Fig. 13B. —42-year-old man with portal hypertension and recurrent
hemorrhage from esophageal varices. Color Doppler sonogram, obtained after
creation of transjugular intrahepatic portosystemic shunt (TIPS), shows
hepatopetal flow (red signal) in IMV. In our anecdotal experience,
persistence of hepatopetal IMV flow is useful ancillary sign of satisfactory
TIPS function if IMV flow was hepatofugal before TIPS creation.
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Some surgeons advocate ligation of large spontaneous portosystemic shunts
during liver transplantation surgery to avert a postoperative steal phenomenon
[7]. In such cases,
preoperative distinction between the splenic vein and the IMV is imperative so
that the correct vein is ligated during the transplant operation. Thus,
Doppler assessment of IMV flow direction in patients with portal hypertension
can provide clinically useful information in several ways.
Summary
The upper abdominal segment of the IMV can be seen on sonography in most
individuals if the pancreas is not obscured. Familiarity with the sonographic
anatomy of the IMV minimizes the risk that it will be mistakenly identified as
the splenic vein and is useful in the evaluation of portal hypertension.
References
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Introduction
Normal Anatomy
