Diagnostic accuracy of contrast-enhanced ultrasound for microvascular invasion of hepatocellular carcinoma

Abstract Background: Microvascular invasion is an independent risk factor for the recurrence of hepatocellular carcinoma (HCC). Early detection and timely treatment can reduce the recurrence and prolong the overall survival of HCC. Contrast-enhanced ultrasound (CEUS) has been validated for their predictive potential of microvascular invasion in HCC patients, although the conclusion remains controversial. Therefore, a meta-analysis is necessary to be conducted to validate the diagnostic value of CEUS for microvascular invasion in HCC, thus supporting guideline development and clinical practice. Methods: Relevant studies reporting the potential diagnostic value of CEUS for microvascular invasion in HCC patients published before February 2022 will be searched in the PubMed, EMBASE, Cochrane Library, and Web of Science. Data will be extracted by 2 researchers independently. The risk of bias will be assessed by the Quality Assessment of Diagnostic Accuracy Studies-2. All of the above statistical analysis will be carried out with Stata 14.0. Results: The results of this study will be published in a peer-reviewed journal. Conclusion: This study will comprehensively evaluate the diagnostic accuracy of CEUS for microvascular invasion in HCC patients, thus providing high-quality evidence to support clinical practice and guideline development.


Introduction
Hepatocellular carcinoma (HCC) is one of the most-common malignancies. [1,2] Although many treatment options are available to HCC patients, the incidence of postoperative recurrence and metastasis remains high. [3,4] Microvascular invasion is one of the independent risk factors for poor prognosis of HCC, which is an important reference for clinicians to select the optimal treatment and assess the risk of recurrence and metastasis. [5][6][7] Currently, pathological examination is the main diagnostic method for HCC, but imaging and serological examinations are also useful in predicting microvascular invasion of HCC. [8][9][10] Ultrasonography is the most commonly used imaging method for early screening of HCC due to the features of simple operations, nonradioactive and noninvasive procedures. [11] Contrast-enhanced ultrasound (CEUS) is a noninvasive diagnostic technique that has been increasingly used in the diagnosis of HCC. [12][13][14] Hepatic artery blood supply is the main lesion of HCC. Microvascular circulation changes when HCC lesions are invaded by microvessels, which can be dynamically examined by CEUS. [15][16][17] Therefore, CEUS is of great importance in predicting microvascular invasion of HCC.
Currently, a consensus on the recognized guidelines for CEUS in predicting microvascular invasion of HCC is lacked due to the subjective determination of operators and various models of machines. Controversial findings have been reported among various studies. [18][19][20][21] Therefore, a meta-analysis is necessary to verify the diagnostic value of CEUS for microvascular invasion of HCC and to support guideline development and clinical practice. In this study, we will evaluate the diagnostic value of CEUS for microvascular invasion of HCC by conducting a meta-analysis, thus obtaining scientific conclusions for clinical practice.

Study registration
The protocol of the systematic review has been registered on Open Science Framework (registration number: DOI 10.17605/ OSF.IO/ZC95V). This diagnostic meta-analysis was conducted in accordance with the Preferred Reporting Items for a Systematic Review and Meta-analysis of Diagnostic Test Accuracy Studies (PRISMA-DTA) statement. [

Reference standards.
Pathology or cytology is the gold standard for the diagnosis of microvascular invasion of HCC.

Outcome measurements.
Outcomes include the pooled sensitivity (SEN), specificity (SPE), positive likelihood ratio, negative likelihood ratio, diagnostic odds ratio, area under the curve, and their 95% confidence intervals.

Exclusion criteria
Literatures with incomplete data; Republished literatures; Case reports, reviews, cellular experiments, or animal experiments.

Data sources and search strategy
Relevant studies reporting the potential diagnostic value of CEUS for microvascular invasion in HCC patients published before February 2022 will be searched in the PubMed, EMBASE, Cochrane Library, and Web of Science databases. In addition, references of included literatures will be manually reviewed. Literature retrieval strategies in the PubMed were shown in Table 1.
2.5. Data collection and analysis 2.5.1. Study selection and data extraction. Two investigators will be independently responsible for literature screening, data extraction and cross-check. Any disagreement will be solved by the third researcher. Missing information will be obtained by contacting the author. Relevant literatures will be first screened by reading the title and abstract. After excluding obviously irrelevant literatures, the full-text will be further reviewed. The screening flow chart of this study was demonstrated in Figure 1. A self-made data extraction form will be used to extract information, including the first author, publication year, regions, types of studies, age and number of participants, diagnostic threshold, outcome indicators, etc.

Quality assessment
The methodological quality of the included studies will be assessed following Quality Assessment of Diagnostic Accuracy Studies-2 criteria, [23] consisting of 4 key domains (patient selection, index test, reference standard, and flow and timing).

Statistical analysis
Statistical analysis will be performed with Stata 14.0 (Stata Corp, College Station, TX). The presence of a threshold effect Table 1 Search strategy (PubMed).

Number
Search terms will be determined by obtaining the Spearman correlation coefficient and observing whether the summary receiver operating characteristic curve has a "shoulder-arm" distribution. The heterogeneity of the non-threshold effects will be tested by the Chi-square test. I 2 50% and P ≥ .1 indicates no heterogeneity, and the data will be analyzed using a fixed-effects model; otherwise, a random-effects model will be adopted. The pooled SEN, SPE, positive likelihood ratio, negative likelihood ratio, diagnosis odds ratio, and their 95% confidence interval will be calculated. In addition, the pooled diagnostic value of CEUS in predicting the microvascular invasion of HCC through the summary receiver operating characteristic and area under the curve will be tested.

Subgroup analysis
Subgroup analyses based on the ethnicity, and follow-up time will be conducted.

Sensitivity analysis
Goodness of fit and bivariate normal analysis will be performed to test the stability of the results.

Publication bias
The publication bias will be determined by Deeks' funnel plot asymmetry test.

Ethics and dissemination
The content of this study does not involve moral approval or ethical review and it will be presented in print or at relevant conferences.

Discussion
Vascular invasion is one of the most important events triggering HCC recurrence and metastasis, and microvascular invasion is one of the vascular invasion modes, which can only be detected by microscopic examination and serves as a marker for predicting early tumor metastasis. [24,25] Therefore, accurate prediction of microvascular invasion in HCC is of great significance for selecting the optimal treatment and assessing the prognosis of HCC. This is the first meta-analysis to comprehensively retrieve and summarize the evidence for CEUS to predict microvascular invasion of HCC. The results of this review will provide a clinical basis for predicting microvascular invasion of HCC and a novel direction for future explorations.