The role of transrectal doppler ultrasound in the evaluation of rectal lesions: a large-sample analysis of 400+ cases

Introduction

Colorectal cancer (CRC) is a common malignancy and a leading cause of cancer-related death worldwide, with approximately two million new CRC cases diagnosed annually (1). In China, CRC is the second most common cancer and the fourth leading cause of cancer-related death (2). A previous study (3) reported that abdominal pain (55%) and hematochezia (46%) are the most common symptoms of CRC; however, these symptoms are often initially attributed to colitis or hemorrhoids, which will be considered first in the general population, leading to delayed diagnosis and treatment, and adverse outcomes. With the trend toward more personalized and stage-specific treatment for rectal cancer, some early-stage tumors can be removed minimally invasively via proctoscopy, while advanced cases may benefit from neoadjuvant chemotherapy. Consequently, precise preoperative diagnosis and rectal lesion staging are essential for optimal patient management.

The common approaches for evaluating rectal tumors include digital rectal examination, along with rigid or flexible proctoscopy. In past decades, cross-sectional imaging, especially transrectal ultrasound (TRUS), has played an important role in the assessment of anorectal diseases. On TRUS, the five layers of the normal rectal wall can be visualized as three hyperechoic and two hypoechoic layers. Thus, TRUS can evaluate the entire bowel wall thickness, the perirectal tissues, and the lymph nodes, helping further characterize tumors. The thickened bowel wall protrudes into the rectal cavity and can be detected on TRUS as a mass, typically appearing as an irregular hypoechoic lesion without an intact submucosal layer at its base. Following recent advances in ultrasound technology, some new techniques, such as contrast-enhanced ultrasound and shear-wave elastography, have been used to diagnose rectal tumors and differentiate between benign and malignant rectal lesions (4-7). However, the cost and convenience of this new technology reduce its suitability for patients, especially as a screening tool.

Color Doppler flow imaging (CDFI) has been extensively used in clinical practice due to its ability to evaluate vascularization patterns non-invasively. Its applications span from abdominal pathologies (hepatic tumors and uterine disorders) to superficial conditions (thyroid/breast nodules, and arthritis), providing valuable hemodynamic information for diagnosis and characterization (8-12). Its widespread adoption stems from the unique capacity of CDFI ultrasonography to provide real-time hemodynamic information while being both safe and cost-effective. CDFI technology has demonstrated excellent diagnostic performance across these diverse clinical scenarios; however, research on its use in TRUS for rectal tumor evaluation is limited. Indeed, to date, no comprehensive studies have systematically investigated the vascular features of rectal tumors using TRUS. We present this article in accordance with the STARD reporting checklist (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1704/rc).

Methods

This retrospective study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments, and was approved by the Institutional Review Board of Sichuan Cancer Hospital (No. SCCHEC-03-2018-029). All the patients signed written informed consent forms before the examination.

From June 2020 to September 2024, the data of 452 patients with rectal lesions were collected for this study. The inclusion criteria were as follows: rectal lesions confirmed by postoperative or endoscopic pathology after TRUS examination, and the receipt of neoadjuvant therapy (NT). The exclusion criteria were as follows: an inability to complete the TRUS examination or unclear images; and/or incomplete pathologic data (i.e., uncertain pathology results requiring further immunohistochemical certification, which were unavailable due to patient withdrawal). Demographic data (including patient age and sex, lesion location and size, vascular characteristics of the lesion, and the receipt of NT in malignant patients), and clinicopathological data [including the pathological type, and for malignant cases, the tumor grade, pathology nodal stage (pN-stage), pathology tumor stage (pT-stage), and Ki-67 expression] were collected from Sichuan Cancer Hospital Picture Archiving and Communication System.

Equipment

The TRUS examinations were performed using the Mylab TWICE ultrasound system (Esaote SpA, Genoa, Italy) equipped with a transrectal biplanar probe (axial and sagittal, TRT33; linear bandwidth, 4–13 MHz; convex bandwidth, 9–3 MHz). The CDFI setting parameters were as follows: frequency, 5.6 MHz; gain, 56%; wall filter, 65 Hz; and velocity scale, 5.0 cm/s.

TRUS examinations

All the TRUS examinations were performed by an experienced radiologist with more than 8 years of experience in gastrointestinal ultrasound. All the patients were instructed to evacuate the bowel before the TRUS examination. The patients were placed in the left lateral decubitus position, and the biplanar probe, covered with a natural rubber latex, was gently inserted into the rectal cavity. If a tumor was found, the location, morphology, margins, echogenicity, and thickness of the lesion were observed and analyzed. Subsequently, the blood supply and blood flow in the lesion were observed by CDFI mode. This mode was set to low flow, and the color gain was increased gradually to obtain optimum color flow. The color box size was set to cover the whole tumor, and the pulse repetition frequency was lowered. The following qualitative and quantitative CDFI parameters were assessed: (I) peak systolic velocity (PSV); (II) end-diastolic velocity (EDV); and (III) resistive index (RI). Each lesion was measured five times, and the largest value was taken.

Statistical analysis

The statistical analyses were performed using GraphPad Prism (version 9.5; GraphPad Software) and MedCalc Statistical Software (version 20.0; MedCalc Software Ltd., Ostend, Belgium). The categorical data are presented as the frequency and percentage. The measurement data are expressed as the mean and standard deviation. Differences between groups were tested using the t-test and one-way analysis of variance for independent variables. A receiver operating characteristic (ROC) curve analysis was performed to assess the discriminatory properties of the studied variables. Spearman’s rank correlation was used to evaluate the correlation among PSV, EDV, RI, and Ki-67 expression. A P value <0.05 was considered statistically significant in all analyses.

Results

Comparison of CDFI parameters in the benign and malignant rectal lesions

The analysis included 452 rectal lesions, of which 428 (94.7%) were malignant, and 24 (5.3%) were benign. Compared with the benign group, the malignant group exhibited significantly higher PSV and RI values (P<0.05) (Table 1, Figure 1). An RI threshold of >0.67 for malignancy detection resulted in a sensitivity of 78% and a specificity of 80% (Figure 2).

Figure 1 Vascular parameters of malignant and benign rectal lesions. (A,B) The benign lesions showed smaller values than the malignant lesions for both PSV (8.6 vs. 20.5 cm/s) and the RI (0.61 vs. 0.71) (the negative in the figure means the direction); (C,D) box-whisker plot of the RI and PSV values in the malignant and benign lesions; the differences were significant. PSV, peak systolic velocity; RI, resistive index.

Figure 2 ROC curves for the RI values between the benign and malignant lesions. AUC, area under the curve; RI, resistive index; ROC, receiver operating characteristic.

Comparison of CDFI parameters between tumor grades

Based on the pathologic grading, the study cohort comprised 59 cases (17.4%) of grade 1 (G1; well-differentiated) adenocarcinomas; 241 cases (71.1%) of grade 2 (G2; moderately differentiated) adenocarcinomas, and 40 cases (11.5%) of grade 3 (G3; poorly differentiated) adenocarcinomas. The PSV values increased as the tumor grade increased. Although the G3 tumors had a higher PSV than the G2 tumors, this difference was not statistically significant (P=0.16). However, the PSV was significantly higher in both the G2 and G3 tumors than in the G1 tumors (all P<0.05). Analysis of RI values revealed a positive correlation with tumor grade, with the G3 (0.77), G2 (0.73), and G1 (0.68) cases demonstrating the highest to lowest values, respectively. The EDV values did not differ significantly among the differentiation grades (Table 2, Figure 3).

Figure 3 Vascular parameters for different tumor grades. (A,B) The G2 tumors had smaller values than the G3 tumors for both PSV (15.3 vs. 36.4 cm/s) and the RI (0.73 vs. 0.93); (C,D) box-whisker plot of the RI and PSV values in different tumor grades. G, grade; PSV, peak systolic velocity; RI, resistive index.

Comparison of CDFI parameters between different pN-stage and pT-stage rectal tumors

A statistically significant difference in PSV was observed among the pN-stage groups. Specifically, the pN2-stage cases exhibited a significantly higher PSV (20.1 cm/s) than both the pN0-stage (16.7 cm/s) and pN1-stage (15.9 cm/s) cases (Table 3). The EDV values did not differ significantly across the pN-stage groups. Among the pT-stage cases, the RI was significantly higher in the pT4-stage cases (0.78) than in the pT1-stage cases (0.70) (Table 4, Figures 4,5).

Figure 4 Box-whisker plot of the RI and PSV values for different T- and N-stage tumors. N, node; PSV, peak systolic velocity; RI, resistive index; T, tumor.

Figure 5 Vascular parameters for different T- and N-stages. (A,B) The N0 tumors had smaller values than the N2 tumors for both PSV (6.5 vs. 35.9 cm/s) and the RI (0.6 vs. 0.88); (C,D) the T1 tumors had smaller values than the T4 tumors for both PSV (12.5 vs. 20.8 cm/s) and the RI (0.65 vs. 0.84). N, node; PSV, peak systolic velocity; RI, resistive index; T, tumor.

Comparison of CDFI parameter changes in NT patients

A total of 34 patients received NT. The Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1 criteria were used to evaluate the efficacy of NT. In 34 NT patients, the PSV and RI values decreased significantly after NT. Compared with the partial response (PR) group and stable disease (SD) group, the PR group showed a higher decrease for both PSV and RI after NT (Table 5, Figure 6).

Figure 6 Vascular parameter changes after NT. (A) Before the NT, the rectal tumors had both higher PSV (20.5 cm/s) and RI (0.89) values; (B) both the PSV (10.1 cm/s) and RI values (0.56) decreased significantly after NT. NT, neoadjuvant therapy; PSV, peak systolic velocity; RI, resistive index.

Ki-67 expression

None of the parameters showed significant correlations with Ki-67 expression.

Discussion

Rectal cancer is one of the most common cancers of the digestive tract. TRUS is the standard local anatomical imaging technique used for rectal lesion diagnosis and rectal cancer staging. Previous studies have shown that TRUS is comparable to computed tomography and magnetic resonance for the evaluation of local invasion and bowel wall penetration in rectal cancer (13,14). TRUS demonstrates high accuracy, ranging from 80–95% for T-staging and 65–85% for N-staging (15-18). Grey-scale sonographic features of benign and malignant solid rectal lesions have been described, and investigators have also used state-of-the-art ultrasonography techniques, such as contrast-enhanced ultrasound and shear-wave elastography, to describe varied rectal lesions (6,7). Despite being the most convenient and prevalent technique, previous studies have not systematically examined the value of TRUS vascular features for rectal tumors.

The differentiation of benign and malignant rectal masses is of great value, as it guides the choice of therapeutic approach. Xu et al. reported that color Doppler ultrasound indicated an abnormally high blood supply inside the tumors, along with a high RI of 0.78 (19). In 2014, Hasab Allah et al. assessed the ability of transabdominal ultrasonographic Doppler flow parameters to differentiate between benign and malignant bowel lesions, and found that malignant lesions had higher RI values than benign lesions (0.64 vs. 0.73), but the difference was not statistically significant (20). We examined the Doppler vascularity of rectal lesions in terms of the RI, PSV, and EDV. The malignant group showed significantly higher PSV and RI values than the benign group. Using an RI threshold >0.67 to indicate malignancy, the sensitivity was 78%, and the specificity was 80%. The present study population was relatively large compared to previous studies; our results could be more convincing. Compared with transabdominal ultrasonography, transrectal examination prevents intestinal gas interference. Our results suggest that high RI and PSV values are strongly indicative of malignant rectal tumors. These results may be attributed to extensive stenosis and occlusions in the neovascularization of differentiated rectal carcinomas, which tend to increase vascular resistance.

In relation to Doppler vascularity and rectal tumor histologic grade, we found that the G3 tumors exhibited higher PSV values than the G2 tumors, and the G2 tumors exhibited higher PSV values than the G1 tumors. In relation to the RI, the G3 tumors exhibited the highest RI values, and the G1 tumors exhibited the lowest RI values. Previous studies have reported similar results for breast cancer. Son et al. found that highly vascular tumors were histologically more aggressive (21). Two other studies reported that G3 tumors tend to exhibit higher quantitative vascularity than lower-grade tumors (10,22).

Further analysis of the correlation between vascular parameters and Ki-67 expression using Spearman’s rank correlation revealed coefficients of −0.11 for PSV and −0.08 for EDV, but no significant differences were found. Previous research on rectal imaging features is limited; Lin et al. reported that parameters obtained noninvasively by dynamic contrast-enhanced ultrasound could predict Ki-67 expression in pancreatic ductal adenocarcinoma preoperatively (23). This new technique could be explored in rectal lesion TRUS research to further examine any possible correlations. This study was the first to attempt to evaluate the relationship between Doppler vascularity and rectal tumor histologic grades; therefore, a large-scale retrospective study of long-term clinical outcomes is needed to validate the study findings.

The role of Doppler ultrasound in staging rectal carcinoma has received more attention than the aforementioned tumor-grade evaluation. Zhang et al. examined 56 rectal cancer patients receiving TRUS and found that the RI decreased as pathological staging increased, while PSV and EDV increased as pathological staging increased (24). In an earlier study by Heneghan et al., a significant difference was observed in terms of the mean PSV between the T1–T2 lesions (19.3±9.2 cm/s) and the T3–T4 lesions (31.5±16.3 cm/s); however, no significant difference in the RI was found between the T1–T2 and T3–T4 lesions (25). Feng et al. (4) showed that PSV and the RI measured by TRUS are useful predictors of pT-stages (pT1–2 vs. pT3, reporting mean PSV values of pT1, pT2, and pT3 of 19.9, 17.4, and 16.8 cm/s, respectively, as well as mean RI values of pT1, pT2, and pT3 of 0.72, 0.78, and 0.73, respectively). Similarly, in our study, the PSV values of pT1, pT2, pT3, and pT4 were 15. 9, 16.8, 16.8, and 18.4 cm/s, and the corresponding RI values were 0.71, 0.73, 0.72, and 0.77. A significant difference was only observed in the RI values between the pT4-stage and the pT1-stage. Further, in terms of the relationship between rectal tumor pN-stage and Doppler vascularity, our study found that the pN2-stage cases had higher PSV values than the pN0-stage and pN1-stage cases (20.1 vs. 16.7 cm/s and 20.1 vs. 15.9 cm/s), and the pN2-stage cases had higher RI values than the pN1-stage cases (0.74 vs. 0.72). These primary pN-stage related results are rare and uncommon and need to be verified in future studies.

In the present study, an analysis of different Doppler parameters of rectal carcinoma by TRUS before and after NT revealed a decrease in the RI and PSV values in all cases. Similarly, in a study of 62 patients, Xu et al. reported a decrease in RI values (19). We also compared the PR and SD groups; the PR group showed a higher decrease in both the PSV and RI values after NT. This decrease in RI and PSV values may be due to the degeneration and necrosis of multiple intra-tumor capillary bed circuits after NT.

This study had several limitations. First, its single-center design may limit the generalizability of the findings. Second, the relatively small number of benign rectal lesions limited the statistical power for subgroup analyses. Future research should involve prospective, multicenter collaborations designed to recruit a substantially larger population, especially of patients with benign pathologies.

Conclusions

TRUS vascular parameters, particularly PSV and RI, demonstrate strong diagnostic value in differentiating between malignant and benign rectal lesions, and differ significantly across some tumor differentiation grades and pN-/pT-stages. Additionally, these parameters can serve as effective biomarkers for monitoring NT efficacy.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STARD reporting checklist. Available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1704/rc

Data Sharing Statement: Available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1704/dss

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1704/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments, and was approved by the Institutional Review Board of Sichuan Cancer Hospital (No. SCCHEC-03-2018-029). All patients signed written informed consent before the examination.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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