Author Affiliations: Department of Ultrasound, Zhongshan Hospital, Fudan University, Shanghai 200032, China (Yuan HX, Cao JY, Kong WT, Xia HS, Wang X and Wang WP)

Corresponding Author: Wen-Ping Wang, MD, PhD, Department of Ultrasound, Zhongshan Hospital, Fudan University, 180 Fenglin Road, Shanghai 200032, China (Tel: +86-21-64041990ext2474; Fax: +86-21-64220319; Email: puguang61@126.com)

 

© 2015, Hepatobiliary Pancreat Dis Int. All rights reserved.

doi: 10.1016/S1499-3872(15)60351-4

Published online March 13, 2015.

 

 

Acknowledgements: We thank Dr. Shao-Hua Lu for pathological figures setup, Drs. Hou-Bao Liu and Tao Suo for data analysis.

Contributors: WWP proposed the study. YHX, CJY and WWP performed research and wrote the first draft. YHX, CJY and KWT collected and analyzed the data. YHX and CJY contributed equally to the article. All authors contributed to the design and interpretation of the study and to further drafts. WWP is the guarantor.

Funding: This study was supported by a grant from the National Natural Science Foundation of China (81371577).

Ethical approval: The study was approved by the Ethics Committee of Zhongshan Hospital of Fudan University, Shanghai, China.

Competing interest: No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article.

 

 

BACKGROUND: Gallbladder adenoma is a pre-cancerous neoplasm and needs surgical resection. It is difficult to differentiate adenoma from other gallbladder polyps using imaging examinations. The study aimed to illustrate characteristics of contrast-enhanced ultrasound (CEUS) and its diagnostic value in gallbladder adenoma.

 

METHODS: Thirty-seven patients with 39 gallbladder adenomatoid lesions (maximal diameter ≥10 mm and without metastasis) were enrolled in this study. Lesion appearances in conventional ultrasound and CEUS were documented. The imaging features were compared individually among gallbladder cholesterol polyp, gallbladder adenoma and malignant lesion.

 

RESULTS: Adenoma lesions showed iso-echogenicity in ultrasound, and an eccentric enhancement pattern, "fast-in and synchronous-out" contrast enhancement pattern and homogeneous at peak-time enhancement in CEUS. The homogenicity at peak-time enhancement showed the highest diagnostic ability in differentiating gallbladder adenoma from cholesterol polyps. The sensitivity, specificity, positive predictive value, negative predictive value, accuracy and Youden index were 100%, 90.9%, 92.9%, 100%, 95.8% and 0.91, respectively. The characteristic of continuous gallbladder wall shown by CEUS had the highest diagnostic ability in differentiating adenoma from malignant lesion (100%, 86.7%, 86.7%, 100%, 92.9% and 0.87, respectively). The characteristic of the eccentric enhancement pattern had the highest diagnostic ability in differentiating adenoma from cholesterol polyp and malignant lesion, with corresponding indices of 69.2%, 88.5%, 75.0%, 85.2%, 82.1% and 0.58, respectively.

 

CONCLUSIONS: CEUS is valuable in differentiating gallbladder adenoma from other gallbladder polyps (≥10 mm in diameter). Homogeneous echogenicity on peak-time enhancement, a continuous gallbladder wall, and the eccentric enhancement pattern are important indicators of gallbladder adenoma on CEUS.

 

(Hepatobiliary Pancreat Dis Int 2015;14:201-207)

 

KEY WORDS: contrast-enhanced ultrasound; discontinuity; gallbladder wall; eccentric enhancement; gallbladder adenoma; homogeneous echogenicity

Gallbladder adenomas are rare tumors that are incidentally found in approximately 0.5% of cholecystectomy specimens.^[1] They are considered pre-cancerous neoplasm requiring surgical resection. At present, it is still difficult to diagnose gallbladder adenomas using imaging means because of their similar features with other benign polyps. It has been reported that diameter ≥10 mm is regarded as the threshold for indicating surgical resection.^[2] However, this strategy usually results in a large number of unnecessary gallbladder resections, because pathological diagnosis proved that some of these lesions were cholesterol polyps, adenomatous hyperplasia or inflammatory polyps. Therefore, differentiating adenoma from other benign polyps would greatly improve the management of these patients and reduce unnecessary cholecystectomies.

 

Contrast-enhanced ultrasound (CEUS) is now widely applied in many fields. CEUS can show the whole process of blood perfusion in the region of interest. It has been investigated in the liver, kidney, breast, thyroid and other organs.^[3-8] Numata et al^[9] evaluated the value of first-generation CEUS agent (Levovist) in gallbladder neoplasms and found that internal tortuous-type vessels could be useful in diagnosing gallbladder carcinoma. Previous studies^{[1, 10]} investigated the diagnostic value of a second-generation CEUS agent (SonoVue) in gallbladder diseases. However, these studies usually focus on how to differentiate malignancy from benign polyps. The study on the differentiation between gallbladder adenomas and other neoplasms is paucity. In the present study, we selected patients with unclear gallbladder lesions under conventional ultrasound, and determined the diagnostic value of CEUS for gallbladder adenomas.

 

 

Between July 2005 and June 2013, 150 patients with suspected gallbladder malignancy who had been diagnosed in community hospitals using ultrasound or computed tomography (CT) visited our department for CEUS examination. Ninety-five of the patients also underwent enhanced CT or magnetic resonance imaging (MRI). Inclusion criteria were as follows: (i) non-mobile, polypoid lesions that protruded into the gallbladder lumen; (ii) for multiple lesions, the lesion larger than 10 mm in diameter; and (iii) absence of the gallbladder wall or adjacent liver parenchyma infiltration.

 

We excluded 107 patients for the following reasons: (1) infiltration into the adjacent liver parenchyma or discontinuity of the gallbladder wall (n=38); (2) the (largest) lesion was smaller than 10 mm in diameter (n=21); (3) cholesterol polyp was diagnosed and followed up with ultrasound (n=19); (4) surgery was contraindicated because of distant metastasis (n=17); (5) metastatic disease in omental lymph nodes was detected during surgery (n=7); and (6) two or more of the above conditions were met (n=5).

 

Forty-three patients with 45 lesions were included. Pathological examination revealed cholesterol polyps (11 lesions), inflammatory polyps (1), tubular adenoma (13), adherent biliary sludge (3), adenomatous hyperplasia (2), carcinoma in adenoma (6), and adenocarcinomas (9). Adenomatous hyperplasia, motionless biliary sludge and inflammatory polyps were excluded from analysis because of infrequency in incidence. The remaining 37 patients with 39 lesions were enrolled in the study.

 

The 39 lesions were divided into 3 groups according to the following pathological results: cholesterol polyps, adenomas and malignancy group. Patients with adenomas associated with canceration were placed into the malignant group. The study was approved by Ethics Committee of Zhongshan Hospital of Fudan University, Shanghai, China. Informed consents were obtained from all study participants. This clinical investigation was conducted according to the principles expressed in the Declaration of Helsinki.

 

All patients fasted for at least 8 hours before examination, and they were scanned in the left lateral decubitus position. The target lesion was investigated using gray-scale and color Doppler ultrasound before CEUS. The lesion was magnified at the best viewing position, ensuring that it was on the ideal plane adjacent to the liver parenchyma for reference and maintained as much as possible in a consistent position. Focus was positioned just below the bottom of the lesion. CEUS was performed by experienced certified technologists using 1.5-7.0 MHz transducers (Philips iU22, Philips Healthcare Solution, Bothell, WA, USA; Technos DU8, Esaote Clinical Solutions, Genoa, Italy; Hivision Preirus, Hitachi, Japan). The transducers were equipped with real-time contrast imaging software. The mechanical index (MI) was set at 0.05-0.10. When CEUS was performed, contrast agent SonoVue (SF6, Bracco, Milan, Italy) was administered as a bolus through the antecubital vein at a dose of 2.4 mL, followed by a flush of 5 mL normal saline. Timer was activated when contrast agent was administered. The target lesion was observed continuously for at least 3 minutes. Another bolus was administered at least 20 minutes later after the first administration if initial enhancement was missed or if the target lesion was changed.

 

We collected patient demographic data such as age and gender. The following features were documented for each lesion: (i) conventional ultrasound: diameter, echogenicity compared with the gallbladder wall (hyperechoic, isoechoic, and hypoechoic), location (bottom, body, and neck), shape (regular or irregular), and homogenicity (homogeneous or heterogeneous); and (ii) CEUS: lesion contrast arrival time, time to iso-enhancement, and time to hypo-enhancement were recorded (compared with the surrounding liver parenchyma of the same depth). The enhancement pattern was classified as eccentric or diffuse enhancement. Eccentric enhancement refers to that the contrast agent goes into the feeding vessels initially from the bottom, then to the peripheral area and the lesion shows a gradually increasing enhancement (Fig. 1). Diffuse enhancement indicates that the contrast agent goes into the whole lesion synchronously with the enhanced extent gradually increasing (Fig. 2). The peak-time appearance was classified as homogeneous or heterogeneous (Fig. 3). The extent of enhancement during the enhancement phase was classified as hyper-, iso-, or hypo-enhancement, with reference to the adjacent liver parenchyma. The "wash-in and wash-out" pattern was compared with the surrounding liver parenchyma. "Fast-in" and "synchronous-in" indicates that the inflow of the contrast agent into the lesions was either faster than or the same as into the adjacent liver parenchyma, respectively. "Fast-out" and "synchronous-out" mean that the outflow of the contrast agent away from the lesions was either faster than or the same as away from the adjacent liver parenchyma, respectively. In our study, the "wash-in and wash-out" pattern of the lesions had the following four types: FF (fast-in and fast-out), FS (fast-in and synchronous-out), SF (synchronous-in and fast-out), and SS (synchronous-in and synchronous-out). The continuity of the gallbladder mucosal line was either complete or incomplete after CEUS.

 

The ultrasound images were reviewed by two blinded radiologists, each with approximately 10 years of experience in abdominal CEUS. The inter-observer variability of each appearance in CEUS (enhancement pattern, peak-time appearance, continuity of gallbladder wall, "wash-in and wash-out" pattern) was assessed by calculating the κ coefficient value after the two blinded radiologists had made their independent interpretation. When they differed, the images were reevaluated together to reach an agreement.

 

The Chi-square test and Fisher's exact test were used to determine the correlation between the pathological types and ultrasonographic data. Continuous variables were expressed as mean±standard deviation (SD), and discrete variables were expressed as numbers and percentages.

 

Statistical analyses were performed using SPSS 18.0 (SPSS, Chicago, IL, USA). A two-tailed P value less than 0.05 was considered statistically significant. A κ value of 1.00 indicated perfect agreement, whereas a κ value of 0 indicated the agreement that should be expected by chance alone. A κ coefficient of >0.75 was considered as very good inter-observer agreement.

 

 

Thirty-seven patients were included in our study. They were 22 women and 15 men, and their age ranged from 24 to 84 years (mean 59.41±18.24). All the patients underwent cholecystectomy (12 laparoscopic cholecystectomies). Solitary polyps were seen in 35 patients, whereas multiple polyps in 2 patients. All the adenomas were of tubular type. The maximal diameter of the lesions ranged from 10 to 35 mm (mean 21.36±8.35) confirmed surgically. We analyzed two pairs of statistics and the details of these cases are summarized in Table 1 (cholesterol polyps vs adenomas groups and adenomas vs the malignancy groups) (κ coefficients of CEUS interpretation made by the two blinded radiologists ranged from 0.78-0.83 which means very good agreement).

 

Compared with the patients with cholesterol polyps, patients with adenomas were significantly older. The lesions were significantly larger, more iso-echogenic, more irregular, a more eccentric enhancement pattern, and a more homogeneous echogenicity at peak-time on CEUS. Compared with the malignancy group, the patients with adenomas had significantly more iso-echogenicity, a smaller sized lesion, a more eccentric enhancement pattern, a longer time to hypo-enhancement, a larger FS pattern, and a more continuous mucosal line integrity after CEUS.

 

We evaluated the diagnostic value of positive indicators, either individual or combination of every two or three. The results with a high diagnostic ability are listed in Tables 2 and 3. Peak-time homogeneous echogenicity on CEUS had the highest diagnostic ability in differentiating gallbladder adenomas from cholesterol polyps with sensitivity, specificity, positive predictive value, negative predictive value, accuracy and Youden index of 100%, 90.9%, 92.9%, 100%, 95.8% and 0.91, respectively. Continuous gallbladder wall on CEUS had the highest diagnostic ability to differentiate adenoma from malignant lesions, with corresponding values of 100%, 86.7%, 86.7%, 100%, 92.9% and 0.87, respectively. Two indicators, iso-echogenicity before CEUS and eccentric enhancement pattern, had significant differences (Tables 2 and 3). We compared the diagnostic ability separately and in combination (Table 4). Eccentric enhancement pattern had the highest diagnostic ability for differentiating gallbladder adenomas from cholesterol polyps and the malignancy group, with sensitivity, specificity, positive predictive value, negative predictive value, accuracy and Youden index of 69.2%, 88.5%, 75.0%, 85.2%, 82.1% and 0.58, respectively.

 

 

Gallbladder adenomas originate from the glandular epithelium of the gallbladder. There is an opportunity for early intervention because they are regarded as pre-cancerous neoplasms.^[11-13] Thus, we collected ultrasound and CEUS images of suspected adenomas and compared adenomas with gallbladder cholesterol polyps and malignant lesions.

 

First, we observed that as patient's age and lesion size increased, the likelihood of the malignancy was increased. Current guidelines recommend ultrasound follow-up for polyps smaller than 10 mm and cholecystectomy for polyps 10 mm or larger.^[14] Terzi et al^[15] concluded that in a patient older than 50 years with gallbladder lesions larger than 10 mm, gallbladder malignancy should be suspected. In our study, the maximum diameter of the biggest adenoma was 35 mm and that of the biggest cholesterol polyp was 25 mm, whereas the smallest malignant lesion was 18 mm. The overlap in lesion size makes it difficult for the clinician to diagnose malignancy simply according to the lesion size.

 

Second, on conventional ultrasound images, echogenicity compared with gallbladder wall showed a descending tendency in the three groups. Cholesterol polyps are composed of clusters of foam cells coated in the gallbladder mucosa. However, they appear hyper-echogenic on endoscopic ultrasound,^[16] whereas adenomas and adenocarcinomas are epithelial tumors that have relatively compact internal structures. This finding may explain the difference between their echogenicity. The morphology of cholesterol polyps is mostly regular in shape, but adenomas and malignant lesions have no particular shape. This characteristic is similar to that of tumors in other organs.

 

To our knowledge, CEUS guidelines do not include the application of CEUS for gallbladder diseases.^{[17, 18]} The use of CEUS for gallbladder diseases was described in several articles. Xie et al^[19] reported that wash-out of the contrast agent within 35-60 seconds after administration may be a key for the diagnosis of gallbladder malignant diseases. The results of our study supported this view. The phenomenon of "fast-in and fast-out" may be related to the tortuous extension of arterial vessels and the presence of small arteriovenous fistulae inside the malignant lesions.

 

Histological differences between cholesterol polyps, adenomas and malignant lesions might explain the heterogenic enhancement of cholesterol polyps and homogenous enhancement of adenomas and malignant lesions on CEUS. Homogeneity at peak-time enhancement was a significant indicator. Large cholesterol polyps were heterogeneous at peak-time enhancement, and honeycomb-like non-enhancement areas were seen inside because of the presence of foam cells (Fig. 4).^[20] However, adenomas and malignant lesions showed homogeneous enhancement of their internal parenchymal structures (Fig. 5). Eccentric enhancement was shown by 69.2% (9/13) of the adenomas. To observe this, we focused on the magnified region of the lesion and maintained the position from the beginning of the enhancement. Dual display mode (gray-scale image and contrast image) was used to avoid deviation from the target area during the contrast process. We replayed the dynamic storage of the contrast process frame by frame to observe the entrance of the contrast agent into the lesion. The enhancement pattern of adenomas was related to its internal supporting vessels. Using color Doppler ultrasound, we observed a solitary vessel perpendicular to the gallbladder wall, and found that its tiny vascular branches were barely visible before CEUS. Real-time CEUS provides a method to observe the lesion's microvasculature. Based on the eccentric enhancement pattern, we suggest that the internal feeding vessel further divides into small branches that travel to every corner of the lesion. Focal nodular hyperplasia of the liver also showed a similar kind of eccentric enhancement.^{[21, 22]} The difference between them is that the vessel supplying the focal nodular hyperplasia branches out from the center of the lesion just like a blossom sign, and the vessel supplying the gallbladder adenomas branch out from the basement like a growing tree. Gallbladder malignant lesions showed diffuse enhancement just like the contrast pattern of hepatocellular carcinoma. The tortuous and irregular vascular distribution brings out the enhancement pattern of the malignant lesions. In the malignancy group of our study, 6 carcinomas were in adenomas. Five of them had a diffuse pattern enhancement and one had an eccentric pattern enhancement. One of the early signs of malignancy was increasing vessel irregularity inside gallbladder adenomas. Correspondingly, the contrast pattern was changed from regular eccentric enhancement to diffuse enhancement. We did not perform further statistical analysis because of the small number of lesions with carcinomas in adenomas. Gallbladder wall discontinuity is also a major sign of gallbladder carcinomas on CEUS.^{[23, 24]} All the patients had a complete gallbladder mucosa line before CEUS, and after CEUS was performed, six patients were diagnosed as having malignancy because gallbladder wall discontinuity was detected. The rate of complete gallbladder wall continuity was high because we excluded the patients with gallbladder wall infiltration or adjacent liver parenchyma infiltration. Lesions with carcinoma in adenoma were difficult to be differentiated from adenocarcinomas by CEUS, and in our study some carcinomas in adenomas also had gallbladder wall discontinuity. All the lesions showed continuous mucosal lines both in the adenomas and cholesterol polyps groups. There was no significant difference between the above two groups. We found that homogeneous peak-time echogenicity, gallbladder wall continuity and eccentric enhancement pattern on CEUS are useful to make differential diagnosis.

 

The limitations of our study including influence by fatty liver because the surrounding liver parenchyma was used as reference of echogenicity on CEUS. Fortunately, only one patient with mild fatty liver was enrolled in our study, so the influence was negligible. The gallbladder wall was enhanced for only 1-2 minutes and it was barely detected during the late enhancement phase; it was thus difficult to set the gallbladder wall echogenicity as a reference on CEUS. Additionally, the comparisons between high and low grade adenomas could not be conducted in our study. Further study is necessary to validate our results.

 

 

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