Objective  To analyze the features of rectal stromal tumors in the endorectal ultrasonography and contrast enhanced ultrasonography (CEUS).

  Methods  The clinical data of patients with rectal stromal tumors who were admitted in the Cancer Hospital, Chinese Academy of Medical Sciences from February 2013 to February 2019 were analyzed retrospectively, including clinical manifestations, CT, MRI, colonoscopy, rectalendorectal ultrasound, and CEUS. According to the consensus on the classification system of National Institutes of Health (NIH), the patients were divided into high-risk, intermediate-risk, low and very low-risk groups. The imaging features of different groups were compared to each other, and the accuracy of different examination methods in the diagnosis of rectal stromal tumors were analyzed.

  Results  A total of 12 patients were included:8 males and 4 females with a median age of 54.0(50.5, 65.25)years. There were 6 cases in very low/low-risk group and 6 cases in intermediate/high-risk group. All of the tumors showed an extroluminal growth pattern, 58.3%(7/12) appearing as oval-shaped, 41.7%(5/12) as lobulated, 91.7%(11/12) with distinct borders, 91.7%(11/12) with heterogeneous echogenicity, 41.7%(5/12) of large tumors with cystic regions, and 91.7%(11/12) with abundant internal blood flow signals. The enhancing mode showed hyper-enhanced with a "fast in and slow out" pattern; the average rise time was (8.10±4.03)s; the average time to peak was (25.54±12.16)s. A total of 5 (83.3%) patients in the intermediate/high-risk group showed inhomogeneous enhancement, centripetal enhancement, perfusion defects. Only one (16.7%) patient in the very low/low-risk group showed similar CEUS feature, and all 6 (100%) patients showed diffuse enhancement. The ratio of correct diagnosis was 60.0% in CT, 66.7% in MRI, 0 in colonoscopy, and 100% in rectal endorectal ultrasound combined with CEUS.

  Conclusion  s The combination of endorectal ultrasonography and CEUS with coupling gel filling the rectum could clearly show the original layer and distribution pattern of rectal stromal tumors, which is helpful for the diagnosis of rectal stromal tumor and accurate risk stratification of the rectal stromal tumor.