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1 Abdominal Imaging, Department of Radiology, University of California, San
Francisco, Box 0628, C-324C, 505 Parnassus Ave., San Francisco, CA
94143-0628.
2 Department of Surgery, University of California, San Francisco, San Francisco,
CA 94143-0628.
Received March 15, 2004;
accepted after revision June 1, 2004.
Address correspondence to B. M. Yeh
(benyeh{at}itsa.ucsf.edu).
Abstract
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MATERIALS AND METHODS. We retrospectively identified 56 living related potential liver donors who underwent both MDCT angiography and MDCT cholangiography. Two reviewers independently rated axial images and 3D reconstructions of MDCT angiograms and cholangiograms as diagnostic or nondiagnostic with respect to depiction of second-order portal venous and biliary tract anatomies. In images rated as diagnostic, second-order portal venous and biliary tract anatomies were categorized as conventional or variant. The concordance between portal venous and biliary tract anatomies was analyzed using McNemar exact chi-square test.
RESULTS. All examinations were diagnostic. Second-order portal venous variants were seen in 10 (18%) and biliary branch variants were seen in 23 (41%) of the 56 patients. Patients with variant portal venous anatomy (6/10, 60%) were more likely to have variant biliary tract anatomy than patients with conventional portal venous anatomy (17/46, 37%; p < 0.01). The sensitivity of variant portal venous anatomy as a marker for variant biliary anatomy was 26% (6/23 patients).
CONCLUSION. Concordance between second-order portal venous and biliary tract anatomies is statistically significant. However, in our series, a number of patients with conventional portal venous anatomy had variant biliary anatomy; therefore, the finding of conventional portal venous anatomy does not obviate preoperative biliary tract imaging in patients before liver donation.
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MDCT Technique
The MDCT technique used varied as the MDCT cholangiographic technique at
our institution evolved during the period of the study. All MDCT scans were
acquired using a 4-MDCT (high-speed [HS] mode, LightSpeed LX/i, GE Healthcare,
n = 8, obtained before February 2002) or a 16-MDCT (LightSpeed, GE
Healthcare, n = 48, obtained during or after February 2002) scanner.
Before MDCT cholangiography, the patients underwent IV contrast-enhanced MDCT
angiography of the abdomen after the administration of 150 mL of iohexol
(Omnipaque 350, Nycomed Amersham) delivered at a rate of 4–5 mL/sec. No
oral contrast material was administered. The abdomen was imaged from the dome
of the diaphragm to the iliac crests with scanning delays of 60 and 120 sec.
Slice thickness was 2.5 mm, and tabletop speed was 27.5 mm/sec for the 16-MDCT
scanner, and 2.5 mm and 27 mm/sec, respectively, for the 4-MDCT scanner.
MDCT cholangiography was performed 1 hr after completion of IV contrast-enhanced MDCT angiography of the abdomen. Before administration of cholangiographic contrast material, each patient received 25 mg IV diphenhydramine (Benadryl, Pfizer) to decrease the rate of allergic reactions to the iodipamide meglumine (Cholografin, Bracco Diagnostics) [8, 14]. Patients examined before January 2003 (n = 41) also received IV morphine sulfate (morphine sulfate in a 5% dextrose injection, Abbott Laboratories) (0.04 mg/kg of body weight) to contract the sphincter of Oddi [15, 16] and possibly improve biliary distention. However, no improvement in the quality of the MDCT cholangiographic images was seen with IV morphine (Breiman RS, unpublished data), and hence, the remainder of the patients (n = 15) were not given morphine. Over a period of 30 min, the patients received an infusion of 20 mL of 52% iodipamide meglumine diluted in 80 mL of normal saline. The liver was imaged during a single breath-hold 15 min after completion of the infusion. Slice thickness was 1.25 and tabletop speed was 13.5 mm/sec for the 8-MDCT scanner, and 2.5 mm and 15 mm/sec, respectively, for the 4-MDCT scanner.
MDCT angiography was performed before (rather than simultaneously with) MDCT cholangiography for three reasons: First, in the event that an allergic reaction to MDCT cholangiographic contrast agent occurred, the MDCT angiography would have already been performed and therefore evaluation of the vasculature would not have been compromised; second, opacified biliary structures would not be confused with opacified arterial or venous structures at image interpretation; and lastly, MDCT reformations of an isolated anatomic structure (vascular tree or biliary tract) would be simpler to create because the other opacified anatomic structures would not need to be digitally removed.
CT cholangiography has been used extensively in Asia [17–20] and Europe [7, 21, 22] and has been described in a few studies in the United States [14, 23–25]. The U.S. Food and Drug Administration has approved the use of iodipamide meglumine for IV contrast-enhanced cholangiography. Nevertheless, all patients were observed for allergic reactions to the contrast material. Patients were observed closely by a nurse or technologist during the infusion of the MDCT cholangiographic contrast material (30-min infusion) and until completion of the MDCT examination. We did not follow up with patients after they left our imaging center. Only one case of mild transient facial urticaria and one case of mild self-limiting wheezing were encountered during the observation period. Neither patient required treatment.
Image Processing and Interpretation
Images were reconstructed at 2.5-mm thickness and 1.25-mm intervals with a
reduced field of view (n = 8) or at 1.25-mm thickness and 0.625-mm
intervals with a reduced field of view (n = 48). Volumetric images
were produced on a 3D graphics workstation (Advantage Windows 4.0 or 3.1, GE
Healthcare) using maximum intensity projection and volume rendering. The MDCT
angiograms and cholangiograms were each evaluated separately in random
sequence without reference to other imaging studies. Two abdominal imaging
radiologists independently reviewed all axial images from the IV
contrast-enhanced abdominal MDCT study on a PACS workstation (AGFA, Mortsel)
and rated the image sets for quality of visualization of the anatomies of the
second-order portal veins and of second-order biliary tract. A study was
considered diagnostic if subjectively judged to be of sufficient quality to
allow clear determination of the second-order branching of the anatomic
structure in question (portal veins or biliary tract). For studies rated as
diagnostic, reviewers also recorded the second-order branching pattern of
portal venous and biliary anatomies.
Second-order branching anatomies of the biliary tract [1] and the portal vein [11] were categorized according to the schema depicted in Figure 1. Briefly, conventional right biliary tract anatomy was defined as the right posterior duct (which drains Couinaud segments VI and VII) draining into the right anterior duct (which drains Couinaud segments V and VIII) to form a right main bile duct. Trifurcation anatomy was defined as the right posterior, right anterior, and left main (which drains Couinaud segments II–IV) ducts joining at the same point to form the common hepatic duct. Low insertion of the right posterior duct was defined as the right posterior duct draining directly into the common hepatic duct. Right posterior duct draining into the left bile duct was defined as the right posterior duct draining into the left main bile duct. Conventional portal venous anatomy was defined as branching at the porta hepatis into the right and left portal veins, with the right portal vein branching into anterior and posterior branches. Trifurcation anatomy was defined as right posterior, right anterior, and left main portal vein branches emanating from the same segment of the main portal vein. Low insertion of the right posterior portal vein was defined as the right posterior segmental portal branch arising from the main portal vein. Right posterior portal vein branching from the left portal vein was defined as right posterior segmental portal vein arising from the left main portal vein.
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Statistical Analysis
Statistical analysis was performed using the Stata software package
(version 7.0, StataCorp). The frequency of portal venous anatomic variants and
biliary anatomic variants was compared using the McNemar chi-square test for
paired samples. A p value less than 0.05 was considered to be
statistically significant.
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The distributions of portal venous and biliary anatomic variants are listed in Tables 2 and 3. In no patient with variant portal venous anatomy was the same subtype of variant biliary tract anatomy observed.
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To our knowledge, extensive evaluation of possible parallel anatomy between portal veins and biliary tract branching variants has not been performed. Cheng et al. [13] reported discordance between the subtypes of second-order portal venous and biliary tract anatomy in 210 patients who had undergone both conventional hepatic arterioportography and conventional cholangiography. Our results are similar to those of Cheng et al. in that we also found discordance between the subtypes of second-order portal venous and biliary tract branching anatomies. Our work adds to that of Cheng et al. in that we also analyzed the portal venous and biliary tract anatomies by classifying them simply as either conventional or variant. When the anatomy was classified in this dichotomous manner, we found a weak concordance between the portal venous and biliary tract anatomies. Indeed, when we analyzed the data published by Cheng et al. in this fashion, we again found a weak concordance (p < 0.01).
The finding of some degree of concordance between portal venous and biliary tract branching variants is likely related to embryology. During embryologic development, the vitelline veins fuse to form the portal vein that ramifies in the liver along the portal tracts. Hepatoblasts adjacent to these tracts differentiate into the ductal plates, eventually leading to the formation of biliary tubular structures [30].
IV contrast-enhanced cholangiography is now rarely performed in the United States, in part because of the perceived high associated rate of allergic reactions to the contrast material [31, 32]. However, recent studies of CT cholangiography have reported a low incidence of adverse effects of 1–3%, which is similar to the incidence of adverse reactions with conventional IV contrast-enhanced CT [9, 33, 34]. The low frequency and mild severity of reactions now described may be due to the use of slow infusion rates and premedication with IV diphenhydramine [23, 33]. We observed only two minor reactions, neither of which required treatment. Additional experience is needed to determine the risks of iodipamide meglumine. Oral contrast-enhanced CT cholangiography has also been evaluated, but in one recent study, this technique showed suboptimal delineation of the biliary tree in 36% of the examinations [24].
Our study has several limitations. We evaluated MDCT cholangiography rather than conventional cholangiography for determination of biliary tract anatomy. Although several reports have shown that MDCT cholangiography has 100% accuracy for depicting second-order biliary tract anatomy using conventional cholangiography as the standard of reference [7, 9, 10], to our knowledge, no large series assessing the accuracy of cholangiography has been published. To address this issue, we assessed all MDCT examinations as being diagnostic for biliary tract and portal venous anatomies before inclusion in our study. Another limitation in our study is the small patient population. However, even with this small sample size, we were able to show that a significant number of patients with both conventional and variant portal venous anatomy have anatomic variants of the biliary tract, and our results are further corroborated by a reanalysis of previously published data.
In conclusion, we found a significant but weak concordance between second-order portal venous and biliary tract anatomies, such that many patients with conventional portal venous anatomy have variant biliary tract anatomy; therefore, the finding of conventional portal venous anatomy does not obviate preoperative biliary tract imaging in patients before liver donation.
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