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Original Research |
1 Department of Radiology and Institute of Radiation Medicine, Seoul National
University Hospital, 28, Yeongeon-dong, Jongno-gu, Seoul 110-744, Korea.
2 Present address: Department of Diagnostic Radiology, Research Institute of
Radiological Science, Yonsei University College of Medicine, Seoul,
Korea.
Received March 31, 2007;
accepted after revision July 30, 2007.
Address correspondence to J. M. Lee
(leejm{at}radcom.snu.ac.kr).
Abstract
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MATERIALS AND METHODS. Two abdominal radiologists retrospectively reviewed by consensus axial images of portal phase MDCT scans of 118 patients who had pathologically confirmed gallbladder cancers; they then reviewed the axial and MPR images from 53 of the 118 patients who had undergone MPR imaging. Local disease spread was evaluated according to the TNM system, and the results were compared with the pathologic findings using the McNemar test. The MDCT performance to differentiate each T-stage was evaluated using Fisher's exact test.
RESULTS. The sensitivities of the ability to differentiate the
T1 versus
T2 lesions,
T2 versus
T3 lesions, and
T3 versus
T4 lesions were 79.3%, 92.7%, and 100%, respectively; the specificities were
98.8%, 86%, and 100%, respectively (p < 0.0001). The overall
accuracy for the T-stage was 83.9%. In the 53 patients with MPR images, the
combined reading of the axial and MPR images increased the diagnostic accuracy
compared with axial image reading only from 71.7% to 84.9%, a statistically
significant degree (p = 0.0233).
CONCLUSION. MDCT provided 83.9% accuracy in the diagnosis of the local extent of gallbladder carcinomas, thereby showing acceptable sensitivity and specificity. The addition of MPR images to the axial CT data increased the accuracy.
Keywords: biliary system gallbladder carcinoma MDCT T-stage
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With the marked development of CT technology, MDCT, which provides high spatial resolution, is now widely used. Several previous studies have shown that MDCT improves the diagnostic accuracy of the staging workup in patients with gastric cancer or colon cancer [7, 8]. To our knowledge, until now there have been no published reports regarding the performance of MDCT in the preoperative evaluation of the local spread of gallbladder carcinomas, including those in patients with early stage cancers. The purposes of this study were to assess the diagnostic performance of MDCT in the T-staging of gallbladder cancer and to evaluate whether the combined interpretation of axial and multiplanar reconstruction (MPR) images improved the diagnostic accuracy compared with axial images only.
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On histopathologic examination, 29 (24.6%) lesions were staged as pT1 (7 pTis, 13 pT1a, 9 pT1b), 39 (33.1%) as pT2, 39 (33.1%) as pT3, and 11 (9.3%) as pT4. Among 53 patients with MPR images, 11 (20.8%) lesions were staged as pT1 (3 pTis, 4 pT1a, 4 pT1b), 18 (34.0%) as pT2, 19 (35.8%) as pT3, and 5 (9.4%) as pT4. One hundred ten of these 118 patients underwent surgery: laparoscopic cholecystectomy (n = 15), open cholecystectomy (n = 35), cholecystectomy and partial hepatectomy (n = 42), and extended radical cholecystectomy (n = 18). In the other eight patients with evident T4 lesions on imaging studies including sonography, CT, and MRI, the diagnosis of gallbladder cancer was established by multiple core needle biopsies of the primary gallbladder lesion as well as of tumors extending into the liver and into two or more adjacent organs.
MDCT Protocol
Patients fasted for at least 8 hours before the examination; no oral
contrast medium or water was given to the patients. CT examinations were
performed with a Brilliance 64 (Philips Medical Systems) (n = 14),
Sensation 16 (Siemens Medical Solutions) (n = 30), LightSpeed Ultra
scanner (GE Healthcare) (n = 40), or MX8000 4-MDCT scanner (Philips
Medical Systems) (n = 34). Each patient received 120 mL of a nonionic
contrast material (iopromide, Ultravist 370, Bayer HealthCare) through an
18-gauge angiographic catheter inserted into a forearm vein. CT scans were
routinely obtained with the patient in a supine position during full
inspiration. The contrast material was injected at a rate of 3 mL/s with an
automatic power injector. MDCT was performed with an MDCT scanner using the
following parameters: detector collimation, 0.75
2.5 mm; table pitch,
1-1.5; kVp, 120; mAs, 170-220; slice thickness, 2.5-5 mm; and reconstruction
intervals, 1.25-5 mm. After an initial unenhanced scan of the upper abdomen
was obtained, MDCT scans were obtained at 65
75 seconds (portal venous
phase) after initiation of the contrast injection.
In 53 patients, to obtain MPR images, 1- to 1.25-mm-thick axial images were reconstructed with 30% overlapping. The MPR images along the long axis and the short axis of the gallbladder were arbitrarily created using a dedicated workstation (Leonardo, Siemens Medical Solutions) by two experienced radiology technicians with at least 5 years of 3D reconstruction experience.
Image Analysis
The CT scans acquired in the 118 patients were reviewed in consensus by two
abdominal radiologists with 13 and 15 years of experience. Although the
reviewers knew that all patients had confirmed gallbladder carcinomas, they
were unaware of the tumor location and size. All CT scans were reviewed on a
PACS workstation (m-view, Marotech). During analysis of the CT features, cases
of each T-stage were randomly intermixed.
According to the TNM classification and related radiologic literature regarding the CT staging of gallbladder cancer [5, 6, 9, 10], we defined the CT criteria for each T-stage (Table 1). The criteria of CT findings for each T category were as follows: T1, polypoid lesions without focal thickening of the gallbladder wall; T2, nodular or sessile lesions associated with focal thickening of the gallbladder wall at what was considered to be attachment sites and with the presence of an apparently smooth fat plane separating the adjacent organs [6]; T3, tumor perforates the serosa (visceral peritoneum) and directly invades the liver or one other adjacent organ or structure (such as the stomach; duodenum; colon; or pancreas, omentum, or extrahepatic bile ducts); and T4, tumor invades main portal vein or hepatic artery or invades multiple extrahepatic organs or structures [9]. In addition to the previously reported CT criteria of T-staging of gallbladder cancer [5, 6], we added some additional criteria regarding T1 and T2 lesions on the basis of our previous experience using radiologic-pathologic correlation. Nodular or flat lesions with mucosal enhancement or focal thickening of the inner enhancing layer of the gallbladder wall with clear, low-attenuated outer wall were regarded as T1 lesions. Regarding T2 lesions, we included the findings of diffuse thickening of the gallbladder wall with heterogeneous enhancement or two-layered enhancement (composed of strong, thick inner-layer enhancement and weak enhancement of the outer layer) and focal wall thickening with outer surface dimpling at the tumor base as criteria for identifying these lesions.
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Statistical Analysis
The diagnostic performance of the MDCT images in terms of differentiating
T1 from
T2,
T2 from
T3, and
T3 from T4 for both
interpretation sessions was evaluated using the Fisher's exact test (GraphPad
InStat, version 3.0, Graph-Pad Software). Differences in the accuracy of the
T-staging in the axial only and the combined MPR images were assessed using
the McNemar test in the MedCalc statistical software, version 6.15.000
(MedCalc Software). Sensitivities and specificities were presented as 95% CIs.
Statistical significance was inferred at a confidence level of 0.05.
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Axial Only and Combined Axial and MPR Data Sets in the Second Interpretation Session
Of the 53 patients for whom MPR images were available, T-staging was
correctly diagnosed in 38 (71.7%) using axial-only data sets and in 45 (84.9%)
using axial and MPR combined data sets. The overall accuracy for T-staging
improved when MPR images were added to axial images (Fig.
5A,
5B,
5C); these differences were
statistically significant (p = 0.0233). Specifically, the diagnostic
performance of the axial-only images and of the combined axial and MPR data
sets in terms of differentiating T1 from
T2,
T2 from
T3, and
T3 from T4, are shown in Table
3. In particular, in terms of differentiating
T2 from
T3, the combined axial and MPR data sets showed statistically significantly
greater accuracy (p = 0.0412).
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Over- and understaging on axial-only images occurred in five (9.4%) of 53 patients and in three (5.7%) of 53 patients, respectively. However, on combined data sets, six (11.3%) of 53 patients were overstaged, and understaging was not observed. Among these, five patients were commonly overstaged on axial-only and combined data sets; three pT1 (2 pTis, 1 pT1a) lesions were misinterpreted as T2 lesions, and two pT2 lesions were misinterpreted as T3 lesions. In addition, on combined data sets, one pT1b lesion was misinterpreted as a T2 lesion. In three understaged patients on axial-only images, one pT2 lesion was interpreted as T1, and two pT3 lesions were interpreted as T2 lesions.
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In our study, the accuracy rate of MDCT in the T-staging of gallbladder cancer (83.9%) was comparable to that in other studies in which helical CT was used [6]. However, considering that our study included many patients with early gallbladder cancer (a total of 68 pT1 and pT2 lesions), absolute comparison with other studies cannot be made. More specifically, the study of Yoshimitsu et al. [6] showed that only one of three patients with T1 gallbladder cancer was correctly diagnosed on CT, which resulted in poor sensitivity (33%) for accurate T1 staging. In contrast, in our data, 23 of 29 pT1 lesions were correctly diagnosed, thereby resulting in relatively high sensitivity (79.3%). Improvement in these results can be expected with the continuing technical development of MDCT [13]. Because of the improved spatial resolution of MDCT compared with that of helical CT, in the diseased or thickened gallbladder wall several findings can help to distinguish the involved layer thereby allowing determination of the accurate T-stage.
Considering the improved spatial resolution of MDCT and the pathologic
criteria for T-staging, we used new CT criteria for distinguishing T1 from T2
lesions. Given that T2 lesions indicate tumoral involvement of the
perimuscular connective tissue layer, the diagnostic criteria suggesting T2
lesions included a nodular lesion with the area of the tumor base dimpled
suggesting involvement of perimuscular connective tissue layer; a flat lesion
with two-layered enhancement or heterogeneous enhancement of the thickened
gallbladder wall, suggesting muscle layer involvement or perimuscular
connective tissue involvement, respectively; and no pericholecystic vessel
involvement. Using these criteria, the accuracies of MDCT in terms of
differentiating T1 from
T2 and
T2 from
T3, were 94.1% and
89.8%, respectively (Table 2).
In previous studies of gallbladder cancer diagnosed on helical CT, the authors
applied morphologic criteria based on previously reported pathologic
observations [11,
14,
15] that most T1 lesions are
polypoid with thin stalks and are typically 2 cm or less in diameter, whereas
T2 lesions tend to be nodular or sessile with focal thickening of the adjacent
gallbladder wall. Distinguishing T1 lesions from T2 lesions on helical CT
using these criteria, however, has been discouraged perhaps because of the
limited spatial resolution achievable with the helical CT technique
[6].
One of the benefits that MDCT can provide is the ability to provide MPR
images in any axis. Several studies have shown that adding MPR images to the
axial images allows improved diagnostic performance of preoperative tumor
staging in gastrointestinal tract malignancies
[7,
8,
13,
16-19].
Our study also revealed that combining MPR images with axial images improved
the accuracy of T-staging of MDCT with axial images (from 71.7% to 84.9%,
p = 0.0233) and permitted differentiation of
T2 lesions from
more advanced stage
T3 lesions (p = 0.0412). We believe that
this improvement could be made with reduced partial volume effects, which are
the drawback of axial images, especially in some transitional zones where the
gallbladder axis is tangential to the scanning plane (Fig.
5A,
5B,
5C). Furthermore, because MPR
shows an oblique coronal plane similar to the surgical plane, this can be
helpful in planning the surgery.
On the other hand, the accuracy was lower in the combined axial and MPR data sets for axials alone than in the total group. This was because more difficult cases were included in the group with MPR images (53 lesions) compared with the total group. Histologically, more cases of flat and papillary tumors were included in the group with MPR images. Twenty-seven (50.9%) of 53 lesions were pathologically proven to be flat (n = 13) or papillary (n = 14) tumors. In our experience, it is difficult to diagnose the local spread of flat lesions, and papillary lesions were frequently overstaged because of their large size and strong enhancement. The relatively high incidence of flat or papillary lesions in the subgroup with MPR images might be the cause of the lower accuracy of the axial-only reading in these 53 patients on MPR images compared with that of the axial image reading in the total 118 patients.
In our study, there were 11 patients with overstaging on MDCT. Among them, seven (63.6%) had papillary growth-type lesions. Two (18.2%) had combined xanthogranulomatous inflammation. In the remaining two patients with pTis and pT1a (18.2%), respectively, pathologic specimens revealed tumor extension through the Rokitansky-Aschoff sinuses, which was invaginated into the muscle layer. Therefore, despite the tumors being confined to the mucosal layer, the exaggerated enhancement of the tumor and muscle layer complex mimicked a T2 lesion and led to overstaging (Fig. 3A, 3B, 3C). The literature suggests that concurrent inflammation around the tumor causes overstaging and that xanthogranulomatous cholecystitis can be found coincidently [6]. On the basis of our results, we believe that radiologists must be aware that lesions can be overstaged in the presence of concurrent inflammation or adenomyomatosis or when the mass shows papillary features.
Alternatively, in our study there were eight understaged lesions. Three (37.5%) of them revealed direct liver invasion less than 3 mm in depth in the gallbladder bed of segment IVb or V. In two of the eight lesions, the time intervals between CT acquisition and surgery were longer than average duration, 25 and 30 days, respectively. Two of these eight lesions had a reconstruction slice thickness of 5 mm, thus causing a partial volume averaging effect. The remaining lesion had subtle tumor infiltration into the muscle layer (Fig. 4A, 4B, 4C). Among the eight understaged lesions on axial-only readings, the three patients who had understaged lesions with focal liver invasion less than 3 mm in depth had MPR images available and when we reviewed the MPR images and axial images, we correctly diagnosed the local liver invasion (Fig. 5A, 5B, 5C).
The limitations of this study include its retrospective nature, consensus reading, and the use of four different MDCT scanners. In addition, there was a potential selection bias in the patient population toward those with less-advanced disease because most of the patients (93.2%, 110/118) we recruited had surgically confirmed lesions.
In conclusion, in our study, MDCT provided 83.9% accuracy in evaluating the T-staging of gallbladder carcinomas. The findings of the combined axial and MPR images allowed improved diagnostic accuracy compared with the results of axial imaging only.
Acknowledgments
The authors thank Dong Chul Kim and Hye Sil Seol of the Department of
Pathology, Seoul National University Hospital, for providing the pathologic
specimens and for their opinions regarding this study. We also thank Bonnie
Hami for her editorial assistance in the preparation of this manuscript.
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