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Original Research |
1 All authors: Department of Clinical Radiology, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka City, Fukuoka 812-8582, Japan.
Received June 28, 2005;
accepted after revision August 22, 2005.
Address correspondence to K. Ishigami
(ishigamikousei{at}aol.com).
Abstract
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MATERIALS AND METHODS. The study group consisted of 118 patients who underwent MDCT with a triple-phase liver protocol with a slice thickness of 5 mm, conventional angiography, and CT hepatic arteriography. The early-phase images of MDCT and conventional angiography were retrospectively reviewed. The presence or absence of an accessory left gastric artery was evaluated using CT hepatic arteriography as the standard of reference. The sensitivity, specificity, and accuracy of MDCT and conventional angiography were calculated.
RESULTS. CT hepatic arteriography revealed an accessory left gastric artery in 25 (21.2%) of 118 cases, including 15 proximal- and 10 distal-type accessory left gastric arteries. On MDCT, there were seven false-negative cases and one false-positive case. Six of the seven false-negative cases were a proximal-type accessory left gastric artery, and nine of 10 distal-type accessory left gastric arteries were correctly diagnosed using MDCT. The sensitivity, specificity, and accuracy of MDCT were 72.0%, 98.9%, and 93.2%, respectively. On conventional angiography, there were three false-negative and two false-positive cases, none of whom underwent selective left hepatic arteriography. Two of the three false-negative cases were the distal-type accessory left gastric artery, but eight of the 10 distal-type accessory left gastric arteries were correctly diagnosed. The sensitivity, specificity, and accuracy of conventional angiography were 88.0%, 97.8%, and 95.8%, respectively.
CONCLUSION. Approximately 70% of accessory left gastric arteries can be diagnosed at the early phase of MDCT even with a slice thickness of 5 mm.
Keywords: Anatomy • Ct Arteriography • Digital Subtraction Angiography • Gastric Arteries • Hemodynamics • Hepatic Arteries • Mdct Angiography
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Hepatic arterial infusion chemotherapy is a treatment of choice for unresectable liver tumors. Percutaneous port-catheter system placement methods using angiographic techniques were developed as a substitute for surgical catheter insertion [4]. During these interventional procedures, the right gastric artery is usually embolized by metallic coils to prevent gastric complications (e.g., ulcer) caused by chemotherapeutic agents. Because the right gastric artery typically arises from the proper hepatic artery, it is not difficult to recognize on angiography. However, an accessory left gastric artery may be mistakenly interpreted to be intrahepatic branches of the left hepatic artery [3, 5-7] and the accuracy of conventional angiography has not been evaluated.
MDCT angiography has been widely used for the evaluation of liver arteries, including the preoperative evaluation of hepatic resections [8, 9], living related liver transplantation donors [10-12], and surgical placement of hepatic arterial infusion chemotherapy pumps [13, 14]. However, little attention has been paid to the diagnosis of an accessory left gastric artery. In addition, MDCT angiography may not be indicated in the setting in which interventional angiographic procedures are subsequently planned. Furthermore, raw MDCT data may not be available in all cases, and retrospective reconstruction with thinner-slice images may not always be possible. Our practical question is, How accurately can MDCT performed using a liver protocol show an accessory left gastric artery in these particular clinical settings?
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The purpose of this study was to assess the diagnostic accuracy of MDCT and conventional angiography for identification of an accessory left gastric artery using CT hepatic arteriography as the standard of reference.
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Imaging Techniques
Triple-phase CT (i.e., hepatic arterial, portal venous, and delayed phases)
was performed with a 4-MDCT scanner (Aquilion, Toshiba Medical Systems; or
Somatom Plus 4 Volume Zoom, Siemens Medical Solutions-Asahi Medical
Technologies) equipped with a gantry rotation time of 0.5 seconds. Each
patient received 100 mL of IV nonionic contrast material containing 370 mg
I/mL (iopamidol [Iopamiron, Schering]) or 350 mg I/mL (iohexol [Omnipaque 350,
Daiichi Pharmaceutical]) by means of an automated power injector at a rate of
2.5 mL/s. The entire liver was scanned in a craniocaudal direction. With the
Aquilion unit, the scanning parameters were as follows: section collimation, 3
mm; section thickness, 5 mm; reconstruction interval, 5 mm; helical pitch,
5.5; 300 mAs; and 120 kVp. With the Somatom Plus 4 Volume Zoom unit, the
scanning parameters were as follows: section collimation, 2.5 mm; section
thickness, 5 mm; reconstruction interval, 5 mm; table feed, 13.8 mm/gantry
rotation; 110 effective mAs; and 120 kVp. Therefore, the parameters were
almost equivalent. The hepatic arterial phase images were obtained at a fixed
delay of 45 seconds after the start of IV contrast material injection. The
portal venous and delayed phase images were acquired at 70 and 240 seconds
after the start of contrast material injection, respectively.
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Imaging Analysis
MDCT, conventional angiography, and CT hepatic arteriography data were
transferred to a commercially available computer workstation (TWS-2000,
Toshiba Medical Systems) for review of hepatic arterial anatomy.
Axial images of the hepatic arterial phase of MDCT studies were retrospectively reviewed by two of the authors without knowledge of the findings of conventional angiography and CT hepatic arteriography. The presence or absence of an accessory left gastric artery was assessed by consensus of the two reviewers. On MDCT, an accessory left gastric artery was shown to be a vessel running through the fissure of the ligamentum venosum (Figs. 1A and 2B). Because an accessory or replaced left hepatic artery arising from the left gastric artery also runs through the fissure of the ligamentum venosum, the reviewers carefully followed the course of the left hepatic and gastric arteries; an accessory left gastric artery is separate from the left gastric artery, and vice versa. An accessory left gastric artery is continuous to the left hepatic artery and appears tapered or tortuous near the cardia of the stomach, at the distal portion of the accessory left gastric artery. In contrast, an accessory or replaced left hepatic artery is continuous to the left gastric artery and appears smaller as it goes through the intrahepatic portion. Reviewers also evaluated variant hepatic arterial anatomy (e.g., replaced right hepatic artery). Neither multiplanar reformation nor maximum intensity projection was used for reviewing the MDCT studies.
Conventional angiography studies were retrospectively reviewed by two of the authors. The reviewers assessed the studies for the presence of an accessory left gastric artery and variant hepatic arterial anatomy by consensus. To determine whether an accessory left gastric artery existed, the reviewers used selective angiography such as left (n = 68), proper (n = 43), and common (n = 7) hepatic arteriography. Celiac and superior mesenteric arteriography images were used to assess variant hepatic arteries. In addition, if reviewers noticed other extrahepatic branches arising from an accessory left gastric artery (Figs. 1B and 3A), they were recorded.
The findings of CT hepatic arteriography were used as the standard of reference. CT hepatic arteriography studies were reviewed by the study coordinator. On CT hepatic arteriography, an accessory left gastric artery was depicted as an enhancing vessel within the fissure of the ligamentum venosum (Figs. 1C and 2D). Contrast enhancement of the cardia and fundus of the stomach was seen (Figs. 1C and 2C). If extrahepatic branches from an accessory left gastric artery existed, CT hepatic arteriography also showed enhancing vessels with contrast enhancement of the corresponding vascular territories (Fig. 3B).
To further evaluate false-negative cases, we divided the origin of the missed accessory left gastric artery into two types: proximal and distal (Fig. 4A and 4B). This classification was modified from the study by Shioyama et al. [7]. The proximal type was defined as occurring when the origin of accessory left gastric artery was between the origin and the proximal two thirds of the left hepatic artery (Figs. 1A, 1B, 1C, 3A, 3B, and 4A). The distal type was defined as occurring when the origin was near the umbilical point (Figs. 2A, 2B, 2C, 2D, and 4B).
Data Analysis
The sensitivity, specificity, and accuracy in the diagnosis of an accessory
left gastric artery on MDCT and conventional angiography were calculated using
the findings of CT hepatic arteriography as the standard of reference.
Conventional angiographic findings of extrahepatic branches from accessory
left gastric artery were compared with those of CT hepatic arteriography.
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On MDCT, an accessory left gastric artery was correctly diagnosed in 17 cases. There was one false-positive case. This case turned out to be an accessory left hepatic artery from the left gastric artery supplying the dorsolateral subsegment of the left hepatic lobe. There were seven false-negative cases in which MDCT could not reveal the accessory left gastric artery. The sensitivity, specificity, and accuracy of MDCT were 72.0%, 98.9%, and 93.2%, respectively. Six (85.7%) of seven false-negative MDCT cases were proximal-type accessory left gastric artery. Nine (90%) of 10 distal-type accessory left gastric artery cases were correctly diagnosed on MDCT. In contrast, only nine (60.0%) of 15 proximal-type accessory left gastric artery cases could be recognized. However, this was not statistically significant (p = 0.102, chi-square test). The cases with false-negative MDCT or false-negative conventional angiography findings are summarized in Table 2.
Conventional angiography correctly showed an accessory left gastric artery in 22 patients. There were two false-positive cases. In one case, the right gastric artery from the left hepatic artery was mistaken for an accessory left gastric artery (Figs. 5A and 5B). In the remaining case, an intrahepatic branch of the left hepatic artery was mistaken for an accessory left gastric artery. There were three false-negative cases in which an accessory left gastric artery was mistakenly considered to be an intrahepatic branch of the left hepatic artery (Figs. 2A, 2B, 2C, and 2D). In these five false-positive and false-negative cases, selective left hepatic arteriography was not performed. The sensitivity, specificity, and accuracy of conventional angiography in diagnosing an accessory left gastric artery were 88.0%, 97.8%, and 95.8%, respectively. In three cases with false-negative conventional angiography findings, two (66.7%) were the distal type. In the remaining case, the peripheral portion of the accessory left gastric artery was not included in the angiography films. Therefore, 14 (93.3%) of 15 proximal-type and eight (80%) of 10 distal-type accessory left gastric arteries were correctly diagnosed using conventional angiography. In addition, extrahepatic branches from an accessory left gastric artery were recognized on conventional angiography in 18 patients (Table 1), including the lower esophagus, diaphragm, mediastinum, and pericardium.
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The most important clinical situation in the diagnosis of an accessory left gastric artery is hepatic arterial infusion chemotherapy, transcatheter arterial chemoembolization, or radioembolization. In fact, a case of gastric perforation that developed after hepatic arterial infusion chemotherapy has been reported [6]. If such a condition is recognized, coil embolization of the accessory left gastric artery would be indicated before placement of a port-catheter system. When transcatheter arterial chemoembolization is performed from the left hepatic artery, the tip of the catheter should be advanced distal to the origin of the accessory left gastric artery. In addition, an accessory left gastric artery can be the site for arterial bleeding from the distal esophagus and proximal stomach [3]. Furthermore, gastric cancer fed by an accessory left gastric artery has been reported [18, 19].
To the best of our knowledge, only one study has described the visualization of an accessory left gastric artery on CT. Ohgiya et al. [5] used single-detector helical CT with 10-mm collimation. They found an accessory left gastric artery in only three (1.8%) of 166 patients, and their findings were 100% accurate. This incidence is much lower than that in our study. Ohgiya et al. used conventional angiography as the standard of reference. However, in their study, selective arteriography of the common or proper hepatic artery was performed in 48 of 166 patients. As they admitted, a limitation of celiac arteriography is that there might have been a substantial number of accessory left gastric arteries that were not recognized on either CT or celiac arteriography in their study.
There are several problems with using conventional angiography to diagnose an accessory left gastric artery. The lateral edge of the left hepatic lobe, the spleen, and the stomach may overlap on celiac arteriography. Especially when the liver lesion is noted in the right lobe, the peripheral portion of an accessory left gastric artery may not be included in the angiography films, and even if it is included, an angiographer may not pay enough attention to the presence of an accessory left gastric artery. Misregistration artifacts from digital subtraction angiography may cause a diagnostic problem when evaluating a small gastric wall stain (Figs. 2A, 2B, 2C, and 2D). In addition, when the stomach is contracted, the gastric wall stain from an accessory left gastric artery may mimic a hypervascular mass [3]. Furthermore, Shioyama et al. [7] reported that the distal type of accessory left gastric artery might be difficult to recognize because it runs close to the dorsolateral branch of the left hepatic artery on angiography.
In our study, selective proper or common hepatic arteriography was performed in all 118 patients. However, there were three false-negative and two false-positive cases on conventional angiography, none of whom underwent left hepatic arteriography. Two of the three false-negative cases were the distal type of accessory left gastric artery. One of the false-positive cases was the right gastric artery arising from the left hepatic artery. This type of arterial branching was noted in six (5.1%) of 118 patients in our study group. However, it is not important to distinguish this type of branching from an accessory left gastric artery because the clinical significance is similar in either case. To correctly diagnose an accessory left gastric artery, it may be desirable to perform left hepatic arteriography, and each of the subsegmental arterial branches of the left hepatic artery should be carefully followed.
Nakamura et al. [3] reported that the incidence of an esophageal branch from an accessory left gastric artery was 71.4% in their angiographic study. In our series, it was 92.0% (23 of 25 patients). In addition, we observed various extrahepatic branches from an accessory left gastric artery, including the diaphragm, mediastinum, and pericardium (Table 1). These arterial branches were not previously described in detail and may also cause adverse effects for hepatic arterial infusion chemotherapy or transcatheter arterial chemoembolization. For example, it has been reported that arterial infusion chemotherapy from the inferior phrenic artery was frequently associated with pulmonary complications [20].
The fissure of the ligamentum venosum is easily recognized on axial CT images because it runs a nearly horizontal course. The vessels running through the ligamentum venosum include an accessory or replaced left hepatic artery arising from the left gastric artery, an accessory left gastric artery, and an aberrant left gastric vein. The incidence of an accessory or replaced left hepatic artery has been reported to be 14.5% [21]. Therefore, the incidences of an accessory or replaced left hepatic artery and an accessory left gastric artery are similar. Although there was one misdiagnosed case in our study, on careful review of the left hepatic and left gastric arteries on axial MDCT images, we could distinguish an accessory left gastric artery from an accessory or replaced left hepatic artery. On the other hand, an aberrant left gastric vein is rare, and the incidence has been reported to be 0.06-0.8% [22, 23]. In our study, an aberrant gastric vein was not encountered. However, an aberrant left gastric vein would have been more confidently excluded on MDCT if we had used the earlier scan delay (e.g., 25-30 seconds) because gastric venous return would happen at the scan delay of 45 seconds [24].
MDCT visualization of an accessory left gastric artery in our cases was not highly sensitive (sensitivity of 72.0%). MDCT was more sensitive in depicting the distal type of an accessory left gastric artery (90%) than the proximal type (60%), although the difference was not statistically significant. The distal type runs a relatively horizontal course, and the proximal type runs obliquely [3, 7], which might be a possible explanation for the different levels of sensitivity on the axial MDCT images. Because the proximal type is not difficult to recognize on conventional angiography, it may be beneficial to be aware of the distal type of accessory left gastric artery by reviewing axial MDCT images before interventional angiographic procedures.
There were several limitations to our study. We used axial MDCT images with a low injection rate of 2.5 mL/s and a fixed scan delay of 45 seconds. MDCT angiography with a narrower collimation, higher injection rate, and earlier scan delay is more suitable for the evaluation of a small artery. In our cases, MDCT with a triple-phase liver protocol was performed with a slice thickness of 5 mm because it was reported that there was little or no advantage in reducing slice thickness to less than 5 mm to detect hypervascular hepatocellular carcinoma [25]. MDCT angiography with thin-slice images (isotropic voxel), obtained by the routine use of 16- and 64-slice scanners, would have improved the accuracy of diagnosing an accessory left gastric artery by making use of multiplanar reformation and maximum intensity projection. Further study is necessary to clarify the value of MDCT angiography for detecting an accessory left gastric artery.
We used CT hepatic arteriography as the standard of reference because we attempted to evaluate the diagnostic accuracy of conventional angiography. On CT hepatic arteriography, it might be difficult to distinguish an accessory or replaced left hepatic artery from an accessory left gastric artery when contrast material flows back into the stomach. On conventional angiography, however, it is not a diagnostic problem to diagnose an accessory or replaced left hepatic artery. In contrast, on MDCT, both an accessory or replaced left hepatic artery and an accessory left gastric artery are seen within the fissure of the ligamentum venosum. Because we also would like to evaluate whether MDCT can distinguish an accessory left gastric artery from an accessory or replaced left hepatic artery, we included patients with an accessory or replaced left hepatic artery who underwent CT hepatic arteriography in the study group. In addition, we excluded patients who underwent CT hepatic arteriography from the right hepatic artery. A substantial number of patients (n = 18) who had variant hepatic arteries were excluded. Furthermore, most of our patients had liver cirrhosis or chronic hepatitis. The morphologic changes of the liver in either setting might change the appearance of an accessory left gastric artery on axial CT images. Finally, retrospective reviews by consensus might cause a source of bias in interpretations.
In summary, approximately 70% of the cases of an accessory left gastric artery can be detected on MDCT even with a slice thickness of 5 mm. MDCT is more accurate for diagnosing the distal type of accessory left gastric artery than the proximal type.
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