Case Report: Transrectal contrast-enhanced ultrasonography on preoperative evaluation of rectal neuroendocrine tumors: a 17-case preliminary study

Objective To evaluate the feasibility of transrectal ultrasound (TRUS) in the sonographic characterization and preoperative assessment of rectal neuroendocrine neoplasms (NENs). Methods Retrospective analysis was performed on the transrectal ultrasound manifestations and clinical data of 17 patients with pathologically and immunohistochemically confirmed rectal NENs [8 cases of rectal neuroendocrine tumors [NETs, G1/G2] and 9 cases of rectal neuroendocrine carcinomas [NECs, G3]] between June 2020 and June 2025. These TRUS findings were compared with the ultrasound features of 31 contemporaneous cases of middle- and lower-segment rectal cancer. Results All 8 rectal NETs (G1, G2) showed hypoechoic masses in the rectal mucosal and submucosal layers on TRUS, with clear borders in 8 cases, point-stripe blood flow signals in 7 cases, and round-shaped lymph nodes with a short diameter > 5 mm in 3 cases; contrast-enhanced ultrasound (CEUS) was performed in 6 cases, showing inhomogeneous hyperenhancement in 2 cases and homogeneous isoenhancement in 4 cases. Among the 9 rectal NECs (G3), 8 presented with localized irregular thickening of the rectal wall, 7 invaded perirectal tissues or organs, all lesions were hypoechoic or heteroechoic with muscularis propria infiltration, and 4 cases had enlarged local lymph nodes. Compared with rectal cancer, the distribution of T stage (T1 vs. T2–4) differed significantly ( P  = 0.016), whereas no significant differences were noted in gender, age, distance from the lower margin of the lesion to the intersphincteric sulcus, lesion length, lesion thickness, or N stage (all P  > 0.05). The overall concordance rate between ultrasonographic staging and surgical pathological staging was 70.6% (12/17) for all rectal NENs, with 87.5% (7/8) for NETs and 55.6% (5/9) for NECs. A limitation of this retrospective feasibility study is its relatively small sample size ( n  = 17), which needs further verification in future multi-center large-sample studies. Conclusions Rectal NETs exhibit characteristic TRUS manifestations and require differentiation from polyps, adenocarcinomas, and inflammatory lesions. Transrectal contrast-enhanced ultrasonography (TR-CEUS), though not widely adopted, is feasible for the preoperative assessment of rectal NENs and may be valuable for follow-up after endoscopic resection to monitor recurrence.