Reply to: Ultrasound Elastography for Differentiating Benign from Malignant Thickened Greater Omentum: Reality or artifact?
by Yixia Zhang (zhangyxia55@163.com)
Zhang Y, Wang X, Tao C, et al. (2016) Ultrasound Elastography for Differentiating Benign from Malignant Thickened Greater Omentum. Eur Radiol 26: 2337-2343Dear Editor,
We thank the authors for their interest in our study. Please see our answers below:
Firstly, as outlined in the discussion section of the paper, we chose abdominal wall as a reference in elastography of the greater omentum for the following reasons: since ascites or moving bowel are the only structures found at the same depth as omental lesions, they are not suitable for reference. Therefore, we had to use the fat or muscle in the abdominal wall as a reference. The abdominal wall tension among patients with ascites is also different, which affected the strain ratio to some degree. Therefore, we recommended that determination of elasticity strain ratios should be performed after abdominal paracentesis for patients with massive ascites. However, ultrasound-guided omental biopsy is the most direct and effective method for diagnosis when compared to elasticity scoring and elasticity strain ratios [1,2].
Secondly, our study showed that enough pressure could be transmitted through the abdominal wall or ascites to the omentum, and thus we could obtain satisfactory elastic images of the thickened greater omentum. The reader suggested that our findings using elastography of the omentum may have been an artifact. Currently, there is no evidence to indicate this. Moreover, our results demonstrated significant differences in elastic imaging of benign and malignant omentum lesions, which were also the objective results of our study. There is no theoretically pure acoustic medium in the human body and we knew that the ascites would partly affect the imaging. To reduce the effects of ascites, we shifted the body position and/or drained the ascites using paracentesis to position the omentum more proximal to the abdominal wall. It was pointed out that in our paper, ascites was found only in front of malignant cases and not in benign cases. In our published manuscript we were unable to provide all examples of elastic images of omentum lesions due to space limitations. However, we can provide some cases of our study here, which clearly show that no matter whether there was ascites or not, the elastic images of benign and malignant lesions can be obtained clearly and show significant differences.
The range of elasticity imaging of line array probe was smaller than that of convex array. There was no ascites in front of the lesion using line array probe. Ascites was seen in the same patient when using convex array probe.
CASE 1
Female, 31 years old, elasticity score: 1, pathological diagnosis: tuberculosis.
Ascites was not found in front of the omentum.
CASE 2
Female, 62 years old, elasticity score: 3, pathological diagnosis: metastatic carcinoma of omentum from ovary tumor.
Ascites was not found in front of the omentum.
CASE 3
Female, 56 years old, elasticity score: 4, pathological diagnosis: metastatic carcinoma of the omentum.
Ascites was not found in front of the omentum.
CASE 4
Female, 23 years old, elasticity score: 2, pathological diagnosis: tuberculosis.
Ascites was found in front of the omentum.
CASE 5
Male, 17 years old, elasticity score:2, pathological diagnosis: tuberculosis.
Ascites was found in front of the omentum.
CASE 6
Male, 27 years old, elasticity score: 4, pathological diagnosis: metastatic carcinoma of omentum from gastrointestinal tract tumor. Ascites was found in front of the omentum.
CASE 7
Female, 57 years old, elasticity score: 3, pathological diagnosis: metastatic carcinoma of omentum from ovary tumor. Ascites was found in front of the omentum.
Thirdly, we agree that some patients with benign diseases such as tuberculosis and liver cirrhosis may also be accompanied by massive ascites. Therefore, the benign or malignant omentum lesions can not be determined by the volume of ascites. Our experience has shown that small metastatic nodules are more often present in the pelvic floor than on the surface of the omentum. Malignant metastasis on the omentum often show diffused omentum thickness like biscuits [2,3]. Therefore, we tried to apply elasticity imaging to differentiate benign lesions from malignant lesions, although there may be some limitations.
To the questions about rigidity and observer bias, our explanation is as follows:
We know that rigidity of lesions may be variable [4]. Rigidity is not only related to the nature of the lesion (benign or malignant), but also to changes that may occur during different pathological phases of the same lesion. For instance, tuberculosis lesions can be predominantly hyperplastic (relatively hard) or predominantly necrotic (relatively soft).
With regards to the question of observer bias, bias is present in each type of ultrasound studies. To reduce possible observer bias, data collection in the our study was performed by 3 clinicians, who each have abundant experience in ultrasound elastography and biopsy.
Ultrasound elastography is a new method, providing valuable information for the differential diagnosis of benign and malignant omental lesions. Just as SE, contrast enhanced ultrasound and other new technologies have been used in the diagnosis of breast lesions, thyroid lesions and other lesions. The development and the application of new technologies may further increase the accuracy of ultrasound diagnosis [5].
I would like to acknowledge the comments from readers who showed great interest in our research. Currently, our team is continuing this research to gain more experience in this technique. We are looking forward to opinions and experience from other facilities that also use ultrasound elastography to differentiate benign from malignant omental lesions.
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